A high-vanadium (V) content V-Ti-Ni shape memory alloy and a preparation method thereof

Abstract

The application discloses a high-vanadium-content V-Ti-Ni shape memory alloy and a preparation method thereof. The method is based on density functional theory simulation to screen the best composition of V-doped Ti-Ni alloy. Then, high-purity sponge titanium, nickel and self-made vanadium-nickel alloy are used as raw materials to smelt, hot forge, twice hot roll and cold draw in a vacuum induction furnace to obtain a high-vanadium-content V-Ti-Ni shape memory alloy wire with a wire diameter of Φ2-Φ3 mm. The hardness and elastic modulus of the final product, the high-vanadium-content V-Ti-Ni shape memory alloy wire, are equivalent to those of conventional Ti-Ni, and the martensitic phase transition temperature is significantly reduced, so that the reversible shape memory effect can be realized in an extremely low-temperature environment, and the high-vanadium-content V-Ti-Ni shape memory alloy wire is suitable for deep sea, deep space exploration and low-temperature micro-actuator manufacturing in a low-temperature environment. The preparation method can be directly applied to an existing Ti-Ni alloy production line without adding special equipment, and the process is economical and cost-effective.

Description

Technical Field

[0001] This invention belongs to the field of new materials with shape memory function, and relates to a V-Ti-Ni shape memory alloy with high vanadium (V) content and its preparation method. Background Technology

[0002] Shape memory alloys (SMAs) are a class of alloys with special properties that can undergo significant shape changes under the influence of temperature variations. SMAs exhibit the shape memory effect, meaning they can remember a certain shape and recover its original shape under specific conditions, demonstrating significant nonlinear deformation characteristics. SMAs can not only sense temperature and displacement but also convert thermal energy into mechanical energy, which can then be output externally as force, energy, or displacement. Commonly used shape memory alloys include titanium-nickel alloys, copper-based alloys, and iron-based alloys; among these three, titanium-nickel-based shape memory alloys have the best memory properties and entered practical applications early on. Key global suppliers of titanium-nickel alloys include Confluent Medical, SAESGetters, ATI, Johnson Matthey, and FortWayne Metals.

[0003] Nickel-titanium-based shape memory alloys (NTiO2) have gained widespread application due to their shape memory effect, pseudoelasticity, and corrosion resistance, holding a dominant position among all shape memory alloys and boasting the largest market share. Furthermore, their performance stability has led to a significant growth rate in recent years. The properties of NTiO2, especially their behavior at different temperatures, are greatly influenced by the alloying elements. For example, vanadium (V) is a key alloying element that can lower the martensitic transformation point (MS) of NTiO2, enabling it to exhibit the shape memory effect at lower temperatures, even room temperature.

[0004] In the prior art, KSBrinkman, PSKorinko, TMAdams, GBRawls Jr (2009) discussed the application of V-Ti-Ni alloys in hydrogen purification systems in their paper "Development of a Non-Noble Metal Hydrogen Purification System". They discussed how the incorporation of vanadium affects the microstructure and properties of the alloy, especially its performance in hydrogen permeability. However, the paper mainly focuses on the application of the alloy in hydrogen purification systems and fails to discuss the preparation method of the alloy in detail, especially the specific production process and performance evaluation of high vanadium content alloys.

[0005] In the prior art, TMAdams, J. Mickalonis (2007) studied the hydrogen permeability of multiphase V–Ti–Ni alloy membranes in the paper "Hydrogen Permeability of Multi-phase V–Ti–Ni Metallic Membranes", and explored how the V content affects the microstructure and hydrogen permeability of the alloy membrane. However, the article mainly focused on the application of V-Ti-Ni alloy membranes, rather than the specific preparation method of shape memory alloys, and the influence of V content on the shape memory effect was not discussed in the whole article.

[0006] In the prior art, E. Balci and F. Dağdele (2021) studied the microhardness and microstructure of Ti-Ni-Nb-X (Ta and V) Shape Memory Alloys in their paper "Investigation of Micro-hardness and Micro-structure of Ti-Ni-Nb-X (Ta and V) Shape Memory Alloys" and explored the influence of vanadium on the alloy's hardness and shape memory properties. However, the paper did not describe in detail the specific preparation methods and applications of V-Ti-Ni alloys, nor did it analyze the shape memory effect under temperature changes.

[0007] In existing research, L. Zou, C. Guo, C. Li, Z. Du (2019) studied the thermodynamic behavior of Ni-Ti-V alloys through experiments and thermodynamic models in their paper "Experimental Investigation and Thermodynamic Modeling of the Ni-Ti-V System," exploring the influence of phase transformation behavior. However, the paper focuses on the thermodynamic model and phase transformation behavior of the Ni-Ti-V system, without introducing specific preparation methods for V-Ti-Ni shape memory alloys, and does not discuss the actual production process and performance of the alloys.

[0008] Furthermore, titanium-nickel based shape memory alloys possess advantages beyond just shape memory effect; they also exhibit pseudoelasticity and corrosion resistance, making them widely applicable in numerous fields. They hold the largest market share among all shape memory alloys. Additionally, the stable properties of titanium-nickel alloys have led to continuously growing market demand, particularly in recent years.

[0009] The difference between low-vanadium and high-vanadium content V-Ti-Ni shape memory alloys lies in their application. Low-vanadium content V-Ti-Ni shape memory alloys are widely used in medical devices because they exhibit shape memory effects at low or room temperatures. However, with the development of high-tech fields such as space exploration and deep-sea research, the demand for high-vanadium content V-Ti-Ni shape memory alloys is gradually increasing. Therefore, high-vanadium content V-Ti-Ni alloys help enhance the performance of materials under special environments, such as extremely low temperatures or complex mechanical loads, leading to a growing demand for their application in these high-tech fields.

[0010] Existing Ti-Ni shape memory alloys are widely used in industrial and medical fields, but their high martensitic transformation temperature limits their functionality in low-temperature environments. To improve this, some technical solutions attempt to regulate alloy properties by adding vanadium (V), a third element. However, most of these methods are based on empirical experiments and rough formulations, lacking systematic theoretical analysis and precise composition design guidance. Furthermore, existing literature contains limited research on the microscopic mechanisms by which V content affects the phase transformation behavior of Ti-Ni alloys, failing to effectively guide industrial manufacturing processes. Therefore, developing a composition design method for high-vanadium-content Ti-Ni shape memory alloys based on theoretical calculations has significant technical and application value. Summary of the Invention

[0011] (1) Purpose of the invention

[0012] To address the shortcomings and defects of existing technologies, this invention proposes a high-vanadium (V) content V-Ti-Ni shape memory alloy and its preparation method. By adjusting the V content in the V-Ti-Ni shape memory alloy to 1%-5% (atomic percentage) vanadium, its stress-induced martensitic phase transformation temperature is reduced, thereby making it suitable for low-temperature applications. Furthermore, the preparation method of this invention can be carried out using existing Ti-Ni shape memory alloy production lines, resulting in low production costs and eliminating the need for additional investment in new equipment.

[0013] The core technical problem to be solved by the present invention is to improve the performance of Ti-Ni shape memory alloy in low-temperature environment, especially by increasing vanadium (V) to reduce the martensitic phase transformation temperature, so that it can work effectively in special low-temperature environments such as deep sea and deep space.

[0014] Specifically, the first technical problem to be solved by the preparation method of the present invention is the realization of shape memory effect under low temperature conditions;

[0015] Specifically, the second technical problem to be solved by the preparation method of the present invention is to determine the optimal content of vanadium (V) after incorporation into Ti-Ni alloy, and to balance the optimal effect on the performance of V-Ti-Ni shape memory alloy;

[0016] Specifically, the third technical problem to be solved by the preparation method described in this invention is to ensure the adaptability and economy of the production process, and to ensure that the high vanadium content alloy can be implemented in different production enterprises.

[0017] The present invention discloses a high vanadium (V) content V-Ti-Ni shape memory alloy and its preparation method. The purpose is to prepare a high vanadium content V-Ti-Ni shape memory alloy with a lower phase transformation temperature and good mechanical properties through precise composition control guided by theoretical calculations, combined with strict melting and multi-pass hot working processes. Moreover, the method has good economic benefits and production compatibility, and is particularly suitable for application fields with special requirements for low-temperature performance.

[0018] Furthermore, regarding the issue of effectively reducing the phase transition temperature while maintaining or optimizing other properties, the primary objective of the preparation method described in this invention is to ensure that the V-Ti-Ni shape memory alloy obtains the expected microstructure and macroscopic properties. Through density functional theory (DFT) simulation calculations, the optimal atomic percentage content of V (vanadium) in the Ti-Ni shape memory alloy was precisely determined to be 1% to 5%, and the atomic percentage ratio of Ti to Ni in the alloy was clearly specified as 49.3:50.7.

[0019] Furthermore, in order to address the adverse effects of obtaining high-performance alloys and reducing alloy impurities, the second objective of the preparation method described in this invention is to use commercially available sponge titanium and nickel with a purity of 99.9% or higher, as well as a self-made vanadium-nickel alloy.

[0020] Furthermore, regarding the problems of alloy element oxidation and gas absorption, a third objective of the preparation method described in this invention is to provide a strictly controlled vacuum induction melting and inert gas protection method, at 1×10 -2 Up to 1×10 -3 The melting process is carried out under a high vacuum of Pa, and argon gas is introduced for protection after melting.

[0021] Furthermore, in order to optimize the microstructure of the alloy, refine the grains, and eliminate casting defects, the fourth objective of the preparation method described in this invention is to provide a multi-pass hot deformation process, including hot forging after peeling and trimming, a first hot rolling and a second hot rolling, and the heating temperature, holding time and final forging temperature of each pass are specifically controlled.

[0022] Furthermore, regarding the issues of texture and mechanical properties of alloy materials, the fifth objective of the preparation method described in this invention is to finalize the dimensions of V-Ti-Ni shape memory alloy wires through cold drawing.

[0023] Furthermore, in order to address the requirement that the alloy can effectively exert its functional properties in low-temperature environments such as deep sea and deep space, the sixth objective of the preparation method described in this invention is to ensure the application potential of the alloy as a material integrating structure and function. Through alloy composition design and process control, the prepared V-Ti-Ni shape memory alloy has a lower stress-induced martensitic phase transformation temperature than the traditional Ti-Ni alloy, while maintaining the hardness and elastic modulus of the V-Ti-Ni shape memory alloy comparable to those of the traditional Ti-Ni shape memory alloy.

[0024] Furthermore, regarding the cost-effectiveness and industrialization feasibility of alloy technology, as well as the common problem of excessively high costs in the development of new materials,

[0025] The seventh objective of the preparation method described in this invention is to propose a complete preparation scheme for V-Ti-Ni shape memory alloys, which can be produced entirely using existing Ti-Ni shape memory alloy production lines without the need for a large investment in new equipment. (2) Summary of the Invention

[0027] Firstly, the preparation method of the high vanadium (V) content V-Ti-Ni shape memory alloy of the present invention includes the following steps:

[0028] S1. Density Functional Theory (DFT) Calculation Optimization of Vanadium (V) Content: The optimal vanadium content range is determined through crystal structure modeling, parameter setting, energy calculation, and performance prediction.

[0029] S1.1 Establishing a crystal structure model: Using the B2 structure of TiNi alloy as the parent crystal, a supercell model is constructed, and the atoms at Ti or Ni sites are systematically replaced with vanadium V atoms to form models with different doping ratios.

[0030] S1.2 Set calculation parameters: Use GGA-PBE functional to perform structural relaxation and energy calculations, and evaluate the total energy, elastic constant and phase transition energy barrier of each doped model;

[0031] S1.3 Doping Scheme Design and Modeling: Vanadium atoms are preferred to replace Ti sites, and the effects of different substitution methods on lattice stability, martensitic phase transformation tendency and electronic structure are compared;

[0032] S1.4 Performance Trend Analysis: Analyze the relationship between doping ratio and performance indicators, and summarize the changes in mechanical properties and martensitic phase transformation temperature under different V contents;

[0033] S1.5 Conclusion Output: Determine the optimal atomic percentage range of vanadium doping, and select the replacement of Ti atoms as the optimal low-temperature phase transformation control range, and then provide feedback to guide the actual alloy composition design and smelting ratio;

[0034] S2. Alloy composition design and batching: First, select and pre-treat the raw materials, then design the alloy composition;

[0035] S2.1 Determine the source of elements and raw materials: Vanadium V, titanium Ti, and nickel Ni are selected as the alloy system, and vanadium V is introduced in the form of nickel V-Ni pre-alloy;

[0036] S2.2 Atomic Ratio Setting: Controlling the vanadium content control range, determining the fixed ratio of titanium and nickel, and constructing a typical vanadium V doping ratio matrix;

[0037] S2.3 Atomic Ratio-Mass Ratio Conversion: Obtain the molar mass of V, Ti, and Ni, convert the above atomic percentages to mass percentages according to any total amount, and perform mass decomposition and conversion for V-Ni pre-alloys;

[0038] S2.4 Mixing process design: Under inert atmosphere or vacuum environment, a V-Ni pre-alloying + Ti mixing strategy is adopted to optimize the mixing method and uniformity detection;

[0039] S2.5 Subsequent Smelting Parameter Recommendations;

[0040] S3. Raw material pretreatment: The determined titanium (Ti), nickel (Ni), and vanadium (V) raw materials are pretreated before smelting;

[0041] S3.1 Material Selection and Acceptance: Sponge titanium, high-purity nickel, and self-made vanadium-nickel alloy are selected as alloy raw materials, and a batch traceability system is established;

[0042] S3.2 Surface pretreatment: The raw material is surface-trimmed and dried;

[0043] S3.3 Proportioning and Weighing: Based on the designed alloy atomic percentage, adjust the amount of pure nickel to be fed after component separation of the vanadium-nickel pre-alloy;

[0044] S3.4 Crushing and Particle Size Control: Repairing alloy principle to control particle size;

[0045] S3.5 packaging for storing raw materials;

[0046] S4. Vacuum induction furnace melting and ingot casting: The alloy batches are melted in a vacuum induction furnace and protected with argon gas, and then cast into ingots;

[0047] S4.1 Raw material charging into the furnace: The Ni, V-Ni pre-alloy and Ti raw materials weighed in proportion are charged into the furnace in sequence;

[0048] S4.2 Vacuum evacuation and preheating: Vacuum evacuation of the furnace cavity and low-temperature preheating of the charge;

[0049] S4.3 Induction heating and melting homogenization: Start medium-frequency induction heating, heat up to melt the alloy raw material, and then stir and hold at the temperature;

[0050] S4.4 Atmosphere switching and argon protection: After the melt stabilizes, argon is introduced to create a positive pressure protective atmosphere;

[0051] S4.5 Casting into ingots: Under argon protection, the melt is poured into a mold and removed after natural cooling;

[0052] S4.6 Billet Removal and Preliminary Inspection;

[0053] S5. Billet trimming and heating homogenization: After peeling and trimming the billet, it is heated and homogenized.

[0054] S5.1 Peeling and trimming: Peel and trim the billet to remove oxide scale, inclusions and irregular parts on the surface, and trim the billet to meet the shape and size specifications of hot forging.

[0055] S5.2 Ingot loading and furnace heating: The trimmed ingots are heated in stages;

[0056] S5.3 Insulation treatment: First, the alloy ingot is insulated, then cooled and the protective atmosphere is maintained;

[0057] S5.4 Ingot billet is removed;

[0058] S6. Hot forging: The billet is hot forged to form a square billet;

[0059] S6.1 Billet trimming: The billet is trimmed by peeling off the skin, and heat preservation or insulation measures are taken at the same time.

[0060] S6.2 Heating of billet before hot forging: The trimmed billet is heated in stages and then kept warm in an inert atmosphere;

[0061] S6.3 Hot forging deformation: The ingot after heat preservation is hot forged to obtain a square billet with a specification of 30mm-60mm;

[0062] S6.4 Billet Cooling and Transfer;

[0063] S7. First hot rolling: The billet is hot rolled in multiple passes to form a rod billet;

[0064] S7.1 Billet Heating: The billet is heated, and real-time monitoring and argon gas protection are performed;

[0065] S7.2 Rolled bar blank: The square billet is hot rolled into a bar blank with a diameter of Φ6 mm to Φ12 mm through a multi-pass hot rolling process;

[0066] S7.3 Cooling and Inspection after Hot Rolling: Cool the bar billet and inspect its quality;

[0067] S8. Second hot rolling: The bar billet is hot rolled in multiple passes to form wire;

[0068] S8.1 Bar billet heating: The bar billet is heated in the furnace while maintaining an inert gas protective atmosphere;

[0069] S8.2 Rolling: The bar billet is hot rolled in multiple passes to form wire with a diameter of Φ2mm-Φ3mm;

[0070] S8.3 Wire cooling and quality inspection;

[0071] S9. Cold drawing: Cold drawing the wire to obtain the final product;

[0072] S9.1 Wire preparation and surface cleaning: Surface cleaning of Φ2mm-Φ3mm wire obtained from the second hot rolling;

[0073] S9.2 Installation and parameter setting of drawing equipment: Assemble the cold drawing equipment and mold, and set the drawing speed, drawing tension and lubrication conditions;

[0074] S9.3 Cold drawing operation: Use multi-segment or continuous drawing method to gradually reduce the diameter of the wire;

[0075] S9.4 Finished product inspection and packaging.

[0076] Furthermore, the preparation method of the high vanadium (V) content V-Ti-Ni shape memory alloy of the present invention includes the following details and parameters:

[0077] Specifically, the crystal structure model established in S1.1 includes: a supercell model of 3×3×3B2TiNi with 54 atoms and a doping ratio of 1%-10%.

[0078] Specifically, S2. Setting the calculation parameters includes the following parameters:

[0079] The energy cutoff is ENCUT = 500eV;

[0080] The grid of point K is 5×5×5;

[0081] The structural relaxation parameters are IBRION=2, ISIF=3, and EDIFFG=–0.02eV / Å.

[0082] The convergence criterion is EDIFF = 1 × 10 -5 eV, NELM=100, PREC=Accurate.

[0083] Specifically, in the design and modeling of the S1.3 doping scheme, the doping model uses the multi-configuration substitution and special quasi-random structure SQS method to simulate the doping behavior of real solid solutions, reflecting the random doping distribution of vanadium atoms in the Ti and Ni lattices.

[0084] Specifically, in the design and modeling of the S1.3 doping scheme, multiple configurations are used to evaluate statistical errors by employing multiple ordered and random replacement configurations, and DFT calculations are performed independently for each configuration.

[0085] Specifically, in the design and modeling of the S1.3 doping scheme, the priority substitution of Ti sites is to use vanadium doping to replace Ti atomic sites in order to reduce lattice distortion and lower the stress-induced martensitic phase transformation temperature.

[0086] Specifically, the performance trend analysis in S1.4 includes the following parameters:

[0087] The structural relaxation parameters are set to IBRION=2 and ISIF=3.

[0088] The energy convergence criterion EDIFF is 1×10. -5 eV,

[0089] The maximum atomic force convergence criterion is 0.02 eV / Å.

[0090] Specifically, in the S1.5 conclusion, the optimal range for low-temperature phase transition regulation is between 1.85% and 5.56%, which is between 1 V / 54 atom and 3 V / 54 atom.

[0091] Specifically, in S2.1, the V:Ni molar ratio of the V-Ni pre-alloy is 1:2, which is determined by the element and raw material source.

[0092] Specifically, the atomic ratio setting in section 2.2 includes the following parameters:

[0093] The atomic percentage of vanadium content is 1%–5%.

[0094] The fixed ratio of titanium to nickel is Ti:Ni = 49.3:50.7.

[0095] The vanadium content in the ratio matrix is ​​set to 1%, 3%, and 5%.

[0096] Specifically, in the S2.3 atomic ratio-mass ratio conversion, the mass breakdown of the V-Ni pre-alloy can be achieved using the following formula:

[0097] in, This represents the mass of vanadium V calculated as an atomic percentage.

[0098] Specifically, the S2.3 atomic ratio-mass ratio conversion includes the following parameters:

[0099] The standard atomic mass of the vanadium is 50.94 g / mol.

[0100] The standard atomic mass of the titanium is 47.87 g / mol.

[0101] The standard atomic mass of the nickel is 58.69 g / mol.

[0102] Based on the standard atomic masses of vanadium, titanium, and nickel, mass ratios corresponding to different vanadium contents were generated.

[0103] Specifically, the S2.4 hybrid process design includes:

[0104] The mixed environment is an inert atmosphere protection box or a vacuum environment;

[0105] The mixed alloy has a particle size range of ≤200 micrometers;

[0106] The tools for detecting the mixing uniformity are energy dispersive spectroscopy (EDS) or scanning electron microscopy (SEM), and the scope of the mixing uniformity detection is to perform quantitative analysis of the composition at each sampling point at the top, middle and bottom of the alloy.

[0107] The deviation range for the mixing uniformity test is ≤±3% for the actual content of any alloying element at any sampling point compared with the theoretical design value.

[0108] Specifically, surface pretreatment in S3.2 includes pickling, mechanical polishing, and ultrasonic cleaning;

[0109] The pickling process uses dilute hydrochloric acid, followed by rinsing with deionized water.

[0110] The mechanical polishing uses 200-400 grit sandpaper.

[0111] The ultrasonic cleaning frequency is 40 kHz and the ultrasonic cleaning duration is 10 min.

[0112] The drying temperature is 70℃-100℃.

[0113] Specifically, in S3.3, the proportioning and weighing process, the internal molar ratio of the V-Ni pre-alloy is V:Ni = 1:2. Therefore, the formula for deducting the amount of pure Ni feed is:

[0114] Firstly, the molar conversion of vanadium mass to molars is as follows:

[0115]

[0116] in, The molar mass of vanadium is approximately 50.94 g / mol.

[0117] Secondly, according to the molar ratio, the corresponding number of nickel moles in the pre-alloy is:

[0118]

[0119] Third, the molar mass of nickel ≈58.69 g / mol, the mass of nickel inherent in the pre-alloy is:

[0120]

[0121] Fourth, the deduction for pure nickel (Ni) input is as follows:

[0122]

[0123] Fifth, the final amount of pure nickel actually weighed out is:

[0124] Specifically, S3.4 crushing and particle size control includes:

[0125] The ball milling process involves introducing high-purity inert argon gas and maintaining a pressure 0.1 MPa ≈ 1 atm higher than atmospheric pressure, and is carried out under Ar atmosphere conditions of 0.1 MPa.

[0126] The ball-to-material ratio of the ball mill is 10:1;

[0127] The ball mill jar has a speed range of medium to high speed and a rotation speed of 300 rpm;

[0128] The time required is 4 hours, and the screening standard is 1mm-5mm.

[0129] Specifically, the S3.5 package storage includes:

[0130] The raw materials are packaged using polytetrafluoroethylene bags or vacuum aluminum foil bags, and are vacuum-sealed or argon-filled.

[0131] The environment for packaging and storage is relative humidity <5% and storage temperature 20℃-25℃.

[0132] Specifically, S4.1, the charging of raw materials into the furnace includes:

[0133] The loading sequence is: Nickel (Ni) → V-Ni pre-alloyed → Titanium (Ti);

[0134] The charge volume accounts for 60%-70% of the furnace cavity volume.

[0135] Specifically, S4.2 vacuum evacuation and preheating treatment includes:

[0136] The vacuum level range is 1×10⁻⁶.-2 Pa—1×10 -3 Pa;

[0137] The vacuum evacuation time is 5 min to 15 min, and the loading is preheated at a low temperature of ≤300℃.

[0138] Specifically, S4.3 induction heating and melting homogenization includes:

[0139] The temperature range for the segmented power gradient is 1300℃–1450℃;

[0140] The heat preservation time is 25 minutes.

[0141] Specifically, the S4.4 atmosphere switching and argon protection process includes:

[0142] The purity of the high-purity argon gas is ≥99.999%, and a positive pressure protective atmosphere of 0.05MPa-0.1MPa is established.

[0143] Specifically, the S4.55 casting process includes:

[0144] The mold is preheated and coated with boron nitride or graphite release agent;

[0145] The preheating temperature of the mold is 150℃-300℃;

[0146] The mold may be a graphite mold or a steel mold.

[0147] Specifically, the S5.1 billet peeling and finishing process includes:

[0148] The dimensional tolerance of the trimmed billet is within ±0.5%, and the processing stress is limited to no more than 10% of the yield strength of the alloy material.

[0149] Specifically, the S5.2 billet charging and heating process includes:

[0150] The heating method adopts a segmented heating program, which is divided into a preheating section of 200℃ / h, a medium-speed section of 100℃ / h, and a final-speed section of 50℃ / h.

[0151] The heating range is 800℃—950℃;

[0152] The temperature holding range is 30 min to 150 min;

[0153] During the furnace loading and heating process, heat-resistant insulation plates are installed at intervals below the furnace loading support and on the side walls.

[0154] Specifically, the S5.3 insulation treatment includes:

[0155] The protective atmosphere is an inert gas or a vacuum;

[0156] The temperature range is 800℃-950℃, and the holding time is 30min-150min;

[0157] The cooling process can be either slow cooling or isothermal cooling.

[0158] The slow cooling rate is 5°C / min.

[0159] The isothermal cooling process involves first maintaining the temperature at 600℃ for 60 minutes, and then cooling at a constant rate of 10℃ / min to the room temperature of 25℃.

[0160] Specifically, the S6.1 billet finishing process includes:

[0161] The dimensional tolerance of the trimmed billet is ≤ ±0.5%;

[0162] The temperature range for heat preservation or insulation is 300℃-400℃.

[0163] Specifically, the pre-forging heating of the ingot in S6.2 includes:

[0164] The heating range is 800℃—950℃;

[0165] The segmented heating is divided into three segments: a preheating segment of 200℃ / h, a medium-speed segment of 100℃ / h, and a final-speed segment of 50℃ / h.

[0166] The inert atmosphere protection is maintained for 30-150 minutes.

[0167] Specifically, S6.3 hot forging deformation includes:

[0168] The final forging temperature is 650℃-700℃;

[0169] The forging speed is 5 mm / s to 20 mm / s, and the forging pressure is 100 MPa to 250 MPa.

[0170] The cross-sectional area is reduced by ≥30%.

[0171] Specifically, the S7.1 billet heating process includes:

[0172] The heating temperature is 800℃-950℃.

[0173] The heating rate is 5℃ / min–15℃ / min.

[0174] The argon gas protection time is 30 min to 120 min.

[0175] Specifically, the S7.2 rolled bar billet includes:

[0176] The rolling speed is 0.1 m / s to 1.0 m / s;

[0177] The deformation per pass is 10%–20%, and the cumulative reduction in cross-sectional area is ≥30%.

[0178] The hot rolling temperature is 850℃-950℃.

[0179] Specifically, S7.3 post-hot rolling cooling and inspection includes:

[0180] The frequency of the ultrasonic testing probe is 5MHz-10MHz;

[0181] The cooling method is either natural air cooling or slow air cooling.

[0182] The cooling rate is 5℃ / min to 20℃ / min.

[0183] Specifically, the S8.1 bar billet heating process includes:

[0184] The heating rate is 5°C / min to 15°C / min;

[0185] The temperature range for the heating is 800℃-950℃, and the temperature uniformity deviation inside the furnace is ≦±10℃.

[0186] The insulation temperature range is 30 min to 120 min.

[0187] Specifically, the S8.2 rolling process includes:

[0188] The rolling speed is 0.05 m / s to 0.5 m / s, the roll gap adjustment accuracy is ≤0.05 mm, and the roll pressure uniformity is ≤5%.

[0189] The total number of passes in the multi-pass hot rolling is 3-10, the deformation per pass is 8%-15%, and the cumulative reduction rate of the multi-pass rolling is ≥30%.

[0190] The rolling temperature is 850℃-950℃, and the rolling zone temperature is set within ±10℃.

[0191] Specifically, S8.3 wire cooling and quality inspection includes:

[0192] The cooling method is natural air cooling or slow air cooling;

[0193] The cooling rate is 5℃ / min—20℃ / min;

[0194] The ultrasonic detection frequency range is 2MHz-10MHz.

[0195] Specifically, the S9.2 drawing equipment installation and parameter setting includes:

[0196] The drawing speed is 0.5m / min to 3m / min, and the drawing die diameter accuracy is ≤ ±0.005mm;

[0197] The drawing tension is 50MPa-150MPa, and the tension fluctuation is ≤5%;

[0198] The lubricant is an oil-based lubricant or a water-based high-performance lubricant.

[0199] Specifically, the S9.3 cold drawing operation includes:

[0200] During the cold drawing process, the single reduction rate is 3%-8%, the cumulative reduction rate is ≥15%, and the tension fluctuation is ≤5%.

[0201] Specifically, S9.4 Finished Product Inspection and Packaging includes:

[0202] The diameter tolerance of the wire is ≤ ±0.01 mm.

[0203] Secondly, a V-Ti-Ni shape memory alloy material with high vanadium (V) content includes the following:

[0204] Specifically, the V-Ti-Ni shape memory alloy material has the following composition by atomic percentage:

[0205] The ratio of titanium to nickel is Ti:Ni = 49.3:50.7;

[0206] The high vanadium content refers to a vanadium element content of 1-5 at.

[0207] Specifically, the V-Ti-Ni shape memory alloy material has the following general chemical formula: Where 1%≤x≤5%.

[0208] Preferably, the optimal composition of the V-Ti-Ni shape memory alloy material, by atomic percentage, is as follows:

[0209] The V2Ti 48.3 Ni 49.7 The shape memory filament has a titanium to nickel ratio of 48.3:49.7 and a vanadium content of 2 at%. The filament exhibits medium grain size and a filament size of 8-20 μm.

[0210] The V5Ti 46.8 Ni 48.2 The shape memory filament has a titanium to nickel ratio of 46.8:48.2 and a vanadium content of 5 at%. The filament exhibits fine grains and a filament size of 5–12 μm.

[0211] The V1Ti 48.8 Ni 50.2 The shape memory filament has a titanium to nickel ratio of 48.8:50.2 and a vanadium content of 1 at%. The filament exhibits medium grain size and a filament size of 10-25 μm.

[0212] The V3Ti 47.8 Ni 49.2 The shape memory filament has a titanium to nickel ratio of 47.8:49.2 and a vanadium content of 3 at%. The filament exhibits medium to fine grains and has a filament size of 8–18 μm.

[0213] Preferably, the V-Ti-Ni shape memory alloy material mainly comprises the following phases:

[0214] The high-temperature austenitic phase B2 is the matrix phase of Ni-Ti shape memory alloy, forming an ordered body-centered cubic structure and exhibiting reversible phase transformation properties.

[0215] The low-temperature monoclinic martensitic phase B19' is a low-temperature phase of shape memory alloys. It transforms from the B2 phase through martensitic phase transformation to form a monoclinic crystal structure, exhibiting alloy shape memory effect and superelastic properties.

[0216] The vanadium-rich V second phase is a reinforcing phase of the shape memory alloy. The second phase is evenly distributed and can refine the grains. It contains intermetallic compounds of Ni3V and Ti2NiV.

[0217] Preferably, the V-Ti-Ni shape memory alloy material can be used as a functional material for deep-sea and deep-space exploration and applied in low-temperature environments.

[0218] (3) Inventive principle

[0219] Part One, the present invention relates to a method for preparing a high-vanadium (V) content V-Ti-Ni shape memory alloy, wherein the chemical formula of the V-Ti-Ni alloy is Ti. 1−x Ni x V y The proportion of vanadium (V) incorporated (y) can optimize the crystal structure and electronic properties of the alloy, thereby effectively reducing the stress-induced martensitic transformation temperature and enabling it to exhibit better shape memory effect at low temperatures. This principle of adjusting alloy properties through vanadium (V) incorporation, combined with density functional theory (DFT) calculations and alloy composition optimization, provides an effective path for developing high-performance V-Ti-Ni shape memory alloys.

[0220] Firstly, the connotation and principle of alloy composition design are as follows:

[0221] Regarding the alloy composition, the introduction of vanadium (V) into the V-Ti-Ni shape memory alloy of this invention aims to improve the alloy's low-temperature performance and martensitic transformation temperature. Specifically, the V-Ti-Ni shape memory alloy exhibits optimal low-temperature performance when the vanadium content is between 1% and 5%. Density functional theory (DFT) calculations can optimize the vanadium doping ratio, ensuring that the V-Ti-Ni shape memory alloy maintains a low stress-induced martensitic transformation temperature at low temperatures. Furthermore, the incorporation of vanadium enhances the stability and deformability of the Ti-Ni-based alloy by altering its electronic structure and mechanical properties.

[0222] Regarding the optimization of vanadium (V) content, the incorporation of vanadium (V) atoms in the preparation method described in this invention can influence the crystal structure of the V-Ti-Ni shape memory alloy, resulting in better performance of the alloy at low temperatures. In particular, it can effectively reduce the stress-induced martensitic transformation temperature, i.e., change the martensitic transformation behavior of the Ti-Ni alloy, thereby lowering the phase transformation temperature of the V-Ti-Ni shape memory alloy and making it suitable for lower temperature environments.

[0223] Secondly, the essence and principle of vacuum induction furnace melting are as follows:

[0224] From the perspective of the melting objective, the preparation method described in this invention employs vacuum induction furnace melting. This vacuum environment avoids interference from oxidation and other impurities, thereby ensuring the purity of the V-Ti-Ni shape memory alloy. During the melting process, in a vacuum environment, by controlling the temperature and the argon protective atmosphere, oxidation of the V-Ti-Ni shape memory alloy can be prevented, improving the alloy's quality and performance.

[0225] From the perspective of argon protection, during the smelting process, argon gas is introduced to prevent the V-Ti-Ni shape memory alloy from reacting with oxygen in the air at high temperatures, thus avoiding oxidation and improving the purity and structural stability of the final V-Ti-Ni shape memory alloy.

[0226] Thirdly, the connotation and principle of hot forging and hot rolling are as follows:

[0227] Regarding the functionality of hot forging, the preparation method described in this invention employs a hot forging process, which enables shaping at high temperatures, adjusts the grain structure of the V-Ti-Ni shape memory alloy, and improves its mechanical properties. Through hot forging, the shape of the ingot is further adjusted, providing a suitable basic shape for subsequent processing. Hot forging also helps eliminate internal stresses that occur during casting, improving the ductility and machinability of the V-Ti-Ni shape memory alloy.

[0228] Regarding the effect of hot rolling, the hot rolling process in the preparation method described in this invention involves repeatedly rolling the ingot or billet to further adjust the size and morphology of the V-Ti-Ni shape memory alloy, while simultaneously improving its mechanical properties and grain structure. After hot rolling, the grain structure of the V-Ti-Ni shape memory alloy is refined, increasing its strength and toughness. The dimensions of the hot-rolled V-Ti-Ni shape memory alloy material are suitable for subsequent cold drawing processing.

[0229] Fourth, the essence and principle of cold drawing are as follows:

[0230] In terms of its application, cold drawing is a process that mechanically stretches V-Ti-Ni shape memory alloy wire at room temperature to further reduce its diameter. This allows the V-Ti-Ni shape memory alloy wire to achieve high strength and dimensional accuracy while maintaining its mechanical properties. The cold drawing process can significantly improve the strength and precision of V-Ti-Ni shape memory alloy wire through strain hardening, thereby meeting the requirements of high-precision applications such as sensors and actuators.

[0231] The second part describes a V-Ti-Ni shape memory alloy with high vanadium (V) content prepared by this invention, based on the following principles.

[0232] Firstly, the chemical formula of the obtained V-Ti-Ni shape memory alloy is as follows:

[0233] The basic chemical formula of the resulting V-Ti-Ni shape memory alloy system is Ti. 1−x Ni x (where x represents the atomic ratio of Ni); This is a common Ti-Ni based shape memory alloy, where the ratio of Ti to Ni is close to 1:1, forming an alloy with a B2 structure;

[0234] In V-Ti-Ni alloys, V atoms replace some metal atoms by incorporating into the positions of Ti or Ni, resulting in the following chemical formula: Ti 1−x Ni x V y ,

[0235] Where y represents the doping ratio of vanadium V, and x+y≤1, the specific vanadium V content range is usually 1% to 5% atomic percentage, that is, the range of y is 0.01 to 0.05.

[0236] Secondly, the principle governing the relationship between the crystal structure and properties of the obtained V-Ti-Ni shape memory alloy is as follows:

[0237] From the perspective of constructing a crystal structure model, a B2 structure model of the Ti-Ni alloy was first established using density functional theory (DFT) calculations. Then, by introducing different proportions of V atoms at the Ti or Ni sites, multiple doping models were constructed to simulate the effect of different vanadium contents on the alloy properties of the V-Ti-Ni shape memory alloy.

[0238] From the perspective of phase transformation and mechanical property analysis, the thermodynamic stability, elastic constants, Young's modulus, shear modulus, and other mechanical parameters of V-Ti-Ni shape memory alloys were calculated under different doping ratios, thereby evaluating the stress-induced martensitic phase transformation temperature of V-Ti-Ni shape memory alloys. Through these calculations, it can be determined that V-Ti-Ni shape memory alloys with a V content of 1%–5% maintain a low phase transformation temperature at low temperatures while exhibiting good mechanical properties.

[0239] Thirdly, the properties of the obtained V-Ti-Ni shape memory alloy are as follows:

[0240] From the perspective of optimizing low-temperature performance, adjusting the V content and Ti-Ni ratio can effectively reduce the phase transformation temperature of the alloy. The incorporation of vanadium can also optimize the alloy's elastic modulus and hardness, making it suitable for use at extremely low temperatures.

[0241] From the perspective of adapting to extreme environments, the final V-Ti-Ni shape memory alloy can not only maintain the shape memory effect at low temperatures, but also has good mechanical strength and corrosion resistance, making it very suitable for extreme environments in the deep sea and deep space.

[0242] (4) Effects of the invention

[0243] This invention discloses a high-vanadium (V) content V-Ti-Ni shape memory alloy and its preparation method. By optimizing the vanadium content using density functional theory, the stress-induced martensitic transformation temperature is significantly reduced without sacrificing hardness and elastic modulus, thus expanding the application potential of Ti-Ni shape memory alloys in low-temperature and extreme environments (such as deep sea and deep space). This invention provides a high-vanadium (V) content V-Ti-Ni shape memory alloy and its preparation method, possessing strong scientific basis and industrial applicability. It ensures the stability of material properties while avoiding the high cost and low efficiency of traditional empirical trial-and-error methods, demonstrating good economic benefits and promotional value.

[0244] The present invention discloses a high vanadium (V) content V-Ti-Ni shape memory alloy and its preparation method, which has significant advantages over traditional shape memory alloy production methods, especially in the improvement of low-temperature applications. That is, the alloy composition and production process of V-Ti-Ni shape memory alloy are optimized, which not only optimizes the performance of Ti-Ni alloy, but also allows production in existing Ti-Ni shape memory alloy production lines, avoiding investment in new equipment and having a high cost performance.

[0245] Specifically, the preparation method described in this invention, guided by precise calculations using density functional theory (DFT), determines the optimal doping range of vanadium (V) in Ti-Ni shape memory alloys from 1% to 5% (atomic percentage), effectively controlling the stress-induced martensitic phase transformation temperature of the alloy, significantly reducing the phase transformation temperature, and enabling the alloy to possess excellent low-temperature shape memory properties.

[0246] Specifically, by employing the preparation method of this invention, through strict control of raw material purity (the purity of titanium, nickel, and vanadium-nickel pre-alloys are all ≥99.9%), precise proportioning design, and high-quality vacuum induction furnace melting process, a high degree of uniformity of alloy composition and dense structure are achieved, avoiding oxidation and impurity contamination, and improving the structural stability of the material.

[0247] Specifically, the hot forging and multi-stage hot rolling processes (including two hot rolling processes and subsequent cold drawing) in the preparation method of the present invention effectively promote grain refinement and dynamic recrystallization, resulting in a high-quality microstructure with uniform grain size and no obvious segregation or inclusions, thereby improving the mechanical properties and plastic processing performance of the alloy.

[0248] Specifically, in the preparation method described in this invention, the wire diameter is further adjusted by a cold drawing process, which achieves high dimensional accuracy (tolerance controlled within ±0.01mm) and excellent surface quality, significantly improving the tensile strength and hardness of the wire, and meeting the needs of high-precision industrial and functional applications.

[0249] Furthermore, the V-Ti-Ni shape memory alloy obtained by this invention significantly reduces the stress-induced martensitic phase transformation temperature while maintaining the hardness and elastic modulus of traditional Ti-Ni alloys. This allows it to be widely used in extreme conditions such as deep-sea exploration and deep-space exploration in low-temperature environments, thus expanding the application range and performance boundaries of shape memory alloys. Attached Figure Description

[0250] Figure 1 This is a process flow diagram of a high vanadium (V) content V-Ti-Ni shape memory alloy and its preparation method according to the present invention;

[0251] Figure 2This is a 1000× resolution as-cast microstructure image of the V-Ti-Ni shape memory alloy with high vanadium (V) content and its preparation method described in this invention. Detailed Implementation

[0252] The present invention will be further described below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited to the scope described in the embodiments.

[0253] The high-vanadium-content V-Ti-Ni shape memory alloy preparation method disclosed in this invention mainly aims to solve the following core technical problems: The performance limitations of existing Ti-Ni-based shape memory alloys in low-temperature environments are that, although traditional Ti-Ni shape memory alloys possess excellent shape memory effect and superelasticity, their stress-induced martensitic transformation temperature is not low enough in extreme low-temperature environments (such as deep sea and deep space), leading to a decrease or failure of their shape memory effect and superelasticity. Therefore, there is an urgent need in the market for a material that can maintain excellent shape memory alloy properties at even lower temperatures.

[0254] The present invention relates to a high vanadium (V) content V-Ti-Ni shape memory alloy and its preparation method. The purpose of the invention is to develop a novel V-Ti-Ni shape memory alloy by introducing an appropriate amount of vanadium and optimizing the preparation process.

[0255] Furthermore, the core objective of the high vanadium (V) content V-Ti-Ni shape memory alloy described in this invention is to significantly reduce the stress-induced martensitic transformation temperature, enabling it to be used in low-temperature and even extreme low-temperature environments, while maintaining hardness and elastic modulus comparable to traditional Ti-Ni shape memory alloys. Moreover, it can be prepared using existing production facilities, thus possessing high economic benefits and application prospects, especially as a functional material in fields such as deep-sea and deep-space exploration.

[0256] Specifically, the present invention discloses a V-Ti-Ni shape memory alloy with high vanadium (V) content and its preparation method, which has a low stress-induced martensitic phase transformation temperature, enabling the V-Ti-Ni shape memory alloy to have better performance in low-temperature environments, making it suitable for exploration in extreme low-temperature environments such as deep sea and deep space.

[0257] Specifically, the present invention discloses a V-Ti-Ni shape memory alloy with high vanadium (V) content and its preparation method. The resulting V-Ti-Ni shape memory alloy has similar hardness and elastic modulus to Ti-Ni shape memory alloy. While maintaining the hardness and elastic modulus of Ti-N alloy, the V-Ti-Ni shape memory alloy has significantly improved low-temperature performance and higher adaptability in specific application scenarios.

[0258] Specifically, the present invention discloses a V-Ti-Ni shape memory alloy with high vanadium (V) content and its preparation method. The resulting V-Ti-Ni shape memory alloy has a vanadium (V) content of 1%–5%, which is considered high vanadium content. By adding an appropriate amount of vanadium (V) to the traditional Ti-Ni shape memory alloy and optimizing the V doping ratio, the phase transition temperature and other physical properties of the shape memory alloy are improved.

[0259] Figure 1 This is a process flow diagram illustrating the production process of the V-Ti-Ni shape memory alloy with high vanadium (V) content and its preparation method according to the present invention. The process includes the following main steps:

[0260] Process 1. Alloy composition configuration (sponge titanium, nickel, vanadium alloy ratio): First, select suitable raw materials, including titanium (Ti), nickel (Ni) and vanadium (V) alloys, and configure them in a certain proportion;

[0261] Process 2. Vacuum Induction Furnace Melting: The raw materials of V-Ti-Ni shape memory alloy are melted in a vacuum induction furnace and processed under vacuum conditions to prevent oxidation and ensure the purity of V-Ti-Ni shape memory alloy;

[0262] Process 3. Casting Ingot: The molten V-Ti-Ni shape memory alloy liquid is poured into an ingot;

[0263] Process 4. Hot forging: The ingot is hot forged and shaped at a specific temperature to form a billet suitable for further processing;

[0264] Step 5. Heat treatment: Heat treatment is performed on the V-Ti-Ni shape memory alloy to optimize the grain structure of the V-Ti-Ni shape memory alloy, eliminate internal stress, and ensure the mechanical properties and shape memory effect of the V-Ti-Ni shape memory alloy.

[0265] Process 6. Hot rolling: The billet undergoes a hot rolling process to further change its shape and process it into V-Ti-Ni shape memory alloy bars;

[0266] Step 7. Cold drawing: Finally, the V-Ti-Ni shape memory alloy material undergoes a cold drawing process to further adjust the diameter, obtaining shape memory alloy wire that meets specific requirements.

[0267] like Figure 1As shown in the process flow diagram, the production steps of the V-Ti-Ni shape memory alloy described in this invention are illustrated. Each step is designed to ensure that the V-Ti-Ni shape memory alloy has good low-temperature performance and stress-induced martensitic phase transformation temperature, while also ensuring the stability and performance of the V-Ti-Ni shape memory alloy in low-temperature environments such as deep sea and deep space.

[0268] Figure 2 This is a 1000× resolution microstructure image of the as-cast V-Ti-Ni alloy, which is a high-vanadium V-content V-Ti-Ni shape memory alloy and its preparation method according to the present invention. It is a scanning electron microscope (SEM) image (1000× magnification) of the V-Ti-Ni shape memory alloy in the as-cast state. It represents the early microstructure results of the high-vanadium content V-Ti-Ni shape memory alloy preparation method of the present invention, reflecting the microstructure characteristics of the V-Ti-Ni shape memory alloy after completing the S2.5 melting step and before entering hot forging or heat treatment.

[0269] like Figure 2 As shown, the microstructure diagram of the V-Ti-Ni shape memory alloy in its as-cast state is magnified by 1000×. Figure 2 The scale bar for the horizontal line is 50µm, the accelerating voltage is 15kV, the observation method is SE (secondary electron imaging), and the sample is in the as-cast state of the high-vanadium V-content V-Ti-Ni shape memory alloy described in this invention, without any subsequent processing or heat treatment. Specifically, Figure 2 The as-cast microstructure of the V-Ti-Ni shape memory alloy exhibits that, during the casting process, varying cooling rates resulted in inhomogeneous grain morphology and phase distribution. The V-Ti-Ni shape memory alloy grains display irregular shapes, prominent grain boundaries, and potential second-phase particles. Using the preparation method described in this invention, the V-Ti-Ni shape memory alloy has a vanadium (V) content of 1%-5% and an atomic percentage ratio of Ti:Ni of 49.3:50.7. Therefore, during subsequent heat treatment processes (such as hot forging, hot rolling, and cold drawing), these grains are optimized, improving the mechanical properties and shape memory characteristics of the V-Ti-Ni shape memory alloy. This results in a final product material with excellent low-temperature performance and shape memory characteristics, suitable for deep-sea and deep-space exploration applications in low-temperature environments.

[0270] Example 1: A specific embodiment of the high vanadium (V) content V-Ti-Ni shape memory alloy and its preparation method according to the present invention.

[0271] The present invention discloses a high vanadium (V) content V-Ti-Ni shape memory alloy and its preparation method. Its main objective is to improve the performance of Ti-Ni shape memory alloy by optimizing the vanadium (V) content, especially to reduce its stress-induced martensitic phase transformation temperature, so that it has better functional performance in low-temperature environments.

[0272] Furthermore, the specific steps of the high vanadium (V) content V-Ti-Ni shape memory alloy and its preparation method described in this invention are as follows:

[0273] S1. Density functional theory calculation: The effect of V doping on the performance of Ti-Ni shape memory alloy was analyzed through density functional theory calculation. After comprehensive analysis, the optimal V-Ti-Ni shape memory alloy with a V content of 1%-5% (atomic percentage) was determined.

[0274] The purpose of the density functional theory calculations is to optimize the V content so that the doping amount in the range of 1% to 5% (atomic percentage) can improve the low-temperature performance of the alloy, especially to reduce the stress-induced martensitic phase transformation temperature of V-Ti-Ni shape memory alloy.

[0275] The advantage of the density functional theory calculation method is that it allows for precise control of the V doping amount, ensuring that the V-Ti-Ni shape memory alloy has better performance at low temperatures.

[0276] S1.1 Establishing a crystal structure model: Based on the TiNi alloy with B2 structure, a 3×3×3 supercell model is constructed to ensure the accuracy of the doping ratio simulation. In addition, some atoms at Ti or Ni positions in the unit cell are systematically replaced with V atoms to construct simulation models with different doping ratios, such as 1%, 2%, 3%, 4%, 5%, 6%, 8%, and 10%.

[0277] S1.11 Selection of the parent crystal structure model: The B2 structure of the parent TiNi alloy is determined to be a cubic crystal with space group Pm-3m, and the standard unit cell parameter (a≈3.015Å) of this structure is obtained as the starting point;

[0278] S1.12 is extended to a supercell model: construct a larger supercell, such as a 3×3×3 B2 supercell containing 54 atoms;

[0279] The purpose of extending to a supercell model is to add different numbers of V atoms into a larger unit cell to accurately simulate the doping behavior of different atomic percentages and reduce the influence of periodic boundary effects on local structural perturbations.

[0280] S1.2 Setting calculation parameters: DFT calculation was performed using VASP software, with GGA-PBE functional, energy cutoff set to 500eV, K-point grid set to 5×5×5, full structure relaxation was applied to minimize lattice energy (ion positions and lattice constants were optimized), and the vacuum layer was set to 15Å to eliminate periodic boundary effects and ensure minimum system energy.

[0281] S1.3 Calculate physical performance parameters:

[0282] Calculate the total energy (E) of each V doping ratio model. total ( ), to compare their thermodynamic stability;

[0283] Calculate the elastic constant (C) 11 C 12 C 44 ), and from this, the conductor modulus (B), shear modulus (G), Young's modulus (E), and other parameters are derived;

[0284] The tendency of stress-induced martensitic phase transformation is assessed by the ΔE difference, i.e. the energy difference between the B2 phase and the R phase or B19' phase;

[0285] Analyze the electronic structure (DOS) and pseudoband gap to determine changes in the electronic stability and conductivity of the alloy;

[0286] S1.4 Performance Trend Analysis: Summarize the effects of different doping ratios on mechanical properties, martensitic phase transformation tendency, and electronic structure properties, and further identify that within the range of 1%-5%V content, both Ti-Ni memory properties can be maintained and the stress-induced martensitic phase transformation temperature can be significantly reduced.

[0287] S1.5 Conclusion Output: It is recommended that the V content be controlled within the range of 1%-5% atomic percentage to provide a quantitative reference for subsequent component design;

[0288] The purpose of the conclusions is to be a key step in transforming the results of the entire DFT calculation and doping simulation into actionable engineering design parameters and alloy proportioning recommendations.

[0289] The composition design of S2.V-Ti-Ni shape memory alloy: the V content in the alloy is 1%–5% (atomic percentage), and the atomic ratio of Ti to Ni is 49.3:50.7;

[0290] The purpose of the composition design of the V-Ti-Ni shape memory alloy is to optimize the alloy's performance by adjusting the V content and Ti-Ni ratio, and to ensure that it has a low stress-induced martensitic transformation temperature at low temperatures.

[0291] The advantage of the composition design of the V-Ti-Ni shape memory alloy is that the composition design of adjusting the V content and Ti-Ni ratio can ensure that the V-Ti-Ni shape memory alloy is comparable to the traditional Ti-Ni alloy in terms of hardness and elastic modulus, while having a lower phase transformation temperature, making it suitable for low-temperature environments in the deep sea and deep space.

[0292] S2.1 Determine the types and sources of elements:

[0293] The selected elements are vanadium (V), titanium (Ti), and nickel (Ni).

[0294] The raw materials are sourced from commercially available sponge titanium (purity ≥99.9%), high-purity nickel (purity ≥99.9%), and self-made vanadium-nickel alloy (V-Ni pre-alloy).

[0295] S2.2 Atomic ratio setting: V content is set to 1%-5% (atomic percentage), Ti:Ni=49.3:50.7 (atomic percentage), and the alloy as a whole is a ternary V-Ti-Ni system;

[0296] S2.3 alloy composition ratio conversion (taking 100g as an example): According to the set atomic percentage, calculate the mass ratio of each element through molar mass, and then accurately weigh each element raw material (or pre-alloy) for experiment or batch preparation.

[0297] S2.4 Mixing method design: Use a mechanical mixer to mix pre-alloyed powders in an inert atmosphere to ensure uniformity, or mix Ti raw materials in vanadium-nickel alloy pre-melt to achieve premixing;

[0298] S2.5 Recommendations for subsequent smelting parameters: Smelting should be carried out using a vacuum induction furnace, with the vacuum level controlled at 1×10⁻⁶. -2 —1×10 -3 Pa, the melt is cast into shape under argon protection to avoid oxidation.

[0299] S3. Raw material pretreatment: Commercially available sponge titanium (purity above 99.9%), nickel (purity above 99.9%), and self-made vanadium-nickel alloy are used as the main raw materials;

[0300] The purpose of the raw material preparation is to ensure the purity and proportioning accuracy of the raw materials for V-Ti-Ni shape memory alloy, so that the final alloy composition and performance meet the expected requirements.

[0301] The advantage of the raw material preparation is that high-purity raw materials help reduce the interference of impurities and improve the structural stability and performance of V-Ti-Ni shape memory alloys.

[0302] The raw material preparation is a key pretreatment step that can ensure the uniformity of V-Ti-Ni shape memory alloy batching, melting stability, microstructure consistency and performance compliance. It involves not only purchasing materials, but more importantly, precise quantification, pretreatment purification, particle control and storage protection.

[0303] S3.1 Raw Material Selection and Acceptance: Commercially available sponge titanium (Ti), high-purity nickel (Ni), and self-made vanadium-nickel pre-alloy (V-Ni) are selected as the main raw materials. According to the design composition, commercially available high-purity sponge titanium (Ti), high-purity nickel (Ni), and self-made vanadium-nickel alloy (V-Ni) are selected. The raw materials are generally in the form of blocks, sheets, or powdered metals. The purity standard of sponge titanium, high-purity nickel, and self-made vanadium-nickel pre-alloy is ≥99.9%, which can be confirmed by chemical analysis (ICP-MS) or supplier COA report.

[0304] For all raw materials, it is important to ensure that the source of vanadium (V) is a stable V-Ni alloy block to avoid the risk of oxidation of elemental vanadium (V).

[0305] The raw materials should have clear composition certificates and quality inspection reports to ensure traceability of origin, purity that meets smelting requirements, and batch number management and traceability records should be established for the raw materials.

[0306] S3.2 Surface pretreatment and impurity removal: Acid washing (such as dilute hydrochloric acid treatment), mechanical polishing, and ultrasonic cleaning are used.

[0307] For metal raw materials, surface oxide scale, oil stains, rust spots and impurities need to be removed; after treatment, rinse with deionized water and dry at 70-100℃ to prevent residual moisture or corrosion from affecting subsequent smelting.

[0308] The surface pretreatment and impurity removal process requires that the material not contain oxide layers, oil films, or other impurities that affect the uniformity of melting. After cleaning, the material must be rinsed with pure water and dried to prevent residual liquid from being carried into the melting system.

[0309] S3.3 Proportion Conversion and Weighing: Based on the atomic percentages of the designed V-Ti-Ni shape memory alloy, Ti:Ni=49.3:50.7, V=1-5at%, it is converted into mass percentages and weighed with high precision, and the weighing error is controlled within ±0.01g.

[0310] The aforementioned ratio conversion and weighing are as follows: when using V-Ni pre-alloy, the vanadium (V) and nickel (Ni) content inside should be verified first, and the corresponding pure nickel (Ni) feeding ratio should be deducted accordingly to ensure that the overall composition meets the set target.

[0311] The ratio conversion and weighing, using V-Ni pre-alloy, need to be adjusted based on the contribution of V and Ni in its composition, and then the amount of pure Ni needs to be adjusted.

[0312] The ratio conversion and weighing should be performed in the order of heavy metals (Ni) first, followed by light metals (Ti) to prevent error amplification. Furthermore, when using V-Ni pre-alloys, it is necessary to calculate the impact of the actual V content (e.g., V:Ni=1:2) on the final ratio.

[0313] S3.4 Crushing and Particle Size Control: For metal raw materials with inconsistent block or particle sizes, cutting, crushing or ball milling can be used to process them to the required particle size. After ball milling, the preferred particle size of powder / particles is controlled within the range of 1–5 mm, which facilitates uniform mixing and melting. Ensuring particle size consistency helps to ensure the uniformity of subsequent mixing and the synchronization of melting rate.

[0314] During the crushing and particle size control process, screening may be performed when necessary to improve mixing uniformity and smelting efficiency. The crushing process should avoid high temperature or exposure to humid air to prevent secondary oxidation of the surface.

[0315] During the crushing and particle size control process, high-temperature oxidation should be avoided during the crushing process. It can be operated in an inert atmosphere or a drying oven. Powdered materials need to be protected from moisture absorption and can be temporarily stored with desiccant.

[0316] S3.5 Packaging, Storage and Labeling: All weighed raw materials should be placed in clean and dry containers. For Ti and V, desiccant should be added or vacuum-sealed to prevent oxidation. They should be sealed and stored in an environment with low humidity <5%RH and temperature 20-25℃.

[0317] In the packaging, storage and labeling process, a raw material list and operation log are established to support process traceability and quality control. That is, each raw material should be labeled with the raw material name, purity, quality, batch ratio, operation date and operator number to facilitate process traceability and quality control.

[0318] For the packaging, storage, and labeling, it is recommended to use polytetrafluoroethylene bags or vacuum aluminum foil bags as packaging materials, and affix labels to record the composition, quality, and date.

[0319] S4. Vacuum Induction Furnace Melting and Casting: Based on the composition of the V-Ti-Ni shape memory alloy, prepare the raw materials, then place the raw materials into a vacuum medium-frequency induction furnace for melting, controlling the vacuum level at 1×10⁻⁶. -2 —1×10 -3 Pa, after the raw material is melted, argon gas is used for protection and then it is cast into an ingot;

[0320] The purpose of the vacuum induction furnace melting is to control the chemical composition, structural uniformity and impurity content in the preparation of V-Ti-Ni shape memory alloy. Through the vacuum melting process, the chemical composition and structure of V-Ti-Ni shape memory alloy are controlled to prevent oxidation problems. At the same time, argon gas is used for protection to ensure the purity of V-Ti-Ni shape memory alloy.

[0321] The advantage of the vacuum induction furnace melting is that the melting process is controlled by vacuum and inert atmosphere. Vacuum and argon protection can effectively prevent the oxidation of raw materials, ensure the purity of the alloy melt, prevent the oxidation of V element, and form a dense and uniform initial ingot structure, thereby improving the quality and performance of V-Ti-Ni shape memory alloy.

[0322] S4.1 Raw material loading into the furnace: Weigh the titanium (Ti), nickel (Ni), and vanadium-nickel pre-alloy (V-Ni) according to the proportion and load them into the graphite crucible or alumina crucible in sequence. Place the crucible in the center of the vacuum medium frequency induction furnace cavity. At this time, the loading amount is controlled within 60%-70% of the furnace cavity volume to prevent splashing or overflow during the melting process.

[0323] The raw material loading sequence is Ni→V-Ni→Ti. Preferably, Ni with higher density is added first, followed by V-Ni pre-alloy and Ti raw material in sequence to ensure uniform loading and avoid the low melting point Ti melting first, which would affect the uniformity.

[0324] For the loading of raw materials, if certain batches of metal raw materials use powder, they should be pre-pressed into blocks to prevent splashing.

[0325] The purpose of loading the raw materials into the furnace is to ensure the stability and compositional uniformity of the V-Ti-Ni shape memory alloy at high temperatures through the vacuum induction furnace melting process implemented in the above steps. This lays a good foundation for subsequent hot forging, hot rolling and cold working processes, and ultimately obtains a high-purity and highly consistent alloy material with shape memory function.

[0326] S4.2 Vacuum Evacuation and Preheating: Start the vacuum system and evacuate the furnace cavity to a vacuum state, preferably controlling the vacuum level at 1×10⁻⁶. -2 —1×10 -3 The vacuum is maintained within the Pa range for 5-15 minutes to stabilize the exhaust and detect the leakage rate. Oxygen and water vapor are discharged to avoid gas interference during the smelting process. Simultaneously, induction preheating is carried out to preheat the charge at a low temperature of ≤300℃ to prevent the metal from boiling and scattering due to moisture absorption.

[0327] The higher the vacuum level in the vacuum pumping and preheating process, the more effective it is in preventing the oxidation of Ti and V and the formation of inclusions.

[0328] During the vacuum evacuation and preheating process, the airtightness is checked to prevent air leakage in the furnace cavity from causing impurities to be drawn back in.

[0329] The vacuum extraction and preheating process, with low-temperature preheating, prevents the raw materials from expanding violently or bursting after absorbing moisture.

[0330] S4.3 Induction heating and melting homogenization:

[0331] Start the medium-frequency induction heating system and gradually raise the temperature to above the melting point, with a preferred melting temperature of 1300℃-1450℃, until all raw materials are completely melted. Use the eddy current effect generated by electromagnetic induction to naturally stir the melt, and control the holding time to 25 minutes.

[0332] During the melting process, the eddy current effect generated by electromagnetic induction is used to naturally stir the melt, so that the alloy composition is fully uniform.

[0333] During the melting process, the heating rate is controlled to avoid Ti splashing or instability of the molten pool. The holding time is then controlled at 25 minutes, or even extended by 2-5 minutes, to ensure that the alloying elements are fully fused.

[0334] In the melting process, if a graphite crucible is used in some cases, the temperature should be controlled to its tolerance limit of ≤1600℃;

[0335] S4.4 Atmosphere switching and argon protection: After the melt stabilizes, high-purity argon (purity ≥99.999%) is slowly introduced into the furnace cavity to establish a positive pressure protective atmosphere. The preferred pressure range is 0.05-0.1MPa to prevent external air backflow and to form an inert atmosphere layer, which further inhibits the oxidation of titanium (Ti) and vanadium (V) at high temperatures.

[0336] During the atmosphere switching and argon protection process, the argon introduction rate must be controlled gently to avoid disturbing the molten pool. Argon can form a protective inert atmosphere layer to further suppress oxidation reactions.

[0337] In the atmosphere switching and argon protection, some systems can use an automatic gas switching program to control the timing of argon charging.

[0338] S4.5 Casting into ingots: The melt is rapidly and steadily poured into a graphite mold or steel mold preheated to 150℃-300℃ under argon protection to form the ingot;

[0339] During the casting process, splashing and air entrapment should be prevented. A graphite layer or boron nitride layer can be pre-coated on the inner wall of the mold to facilitate demolding. After the casting process, the ingot needs to be naturally cooled to room temperature before being removed.

[0340] The casting process should be rapid but steady to prevent air entrapment and splashing.

[0341] The mold used for casting ingots can be coated with a carbon coating or boron nitride coating to facilitate demolding.

[0342] The ingots are cast and then allowed to cool naturally to room temperature to avoid cracking from sudden cooling.

[0343] S4.6 Ingot Removal and Preliminary Inspection: After cooling, the alloy ingot is inspected for shrinkage cavities and cracks on the alloy surface. The yield is recorded by weighing, the composition ratio is checked, and then it is numbered and labeled. The composition ratio, furnace number and date are recorded.

[0344] When the ingot is removed and preliminarily inspected, a small sample may be cut out if necessary for subsequent composition analysis or metallographic observation.

[0345] When the billet is removed and initially inspected, attention should be paid to whether the yield of a certain batch is too low, which indicates a problem of melting loss or spatter.

[0346] S5. Billet trimming and heating homogenization: After casting, the billet is trimmed and then placed in a box furnace for heating and held at 800-950℃ for 30-150 minutes.

[0347] The purpose of the billet trimming and heating is to adjust the grain structure of the V-Ti-Ni shape memory alloy through the heat treatment process, eliminate internal stress, and prepare for subsequent hot forging.

[0348] The billet trimming and heating effectively eliminates surface defects and internal stresses, and optimizes the uniformity of the alloy grain structure, ensuring the improvement of the alloy's plasticity and structural stability in the subsequent hot forging stage, thereby improving the product's forming quality and performance consistency.

[0349] The advantage of the billet trimming and heating is that proper heating and heat preservation can improve the plasticity and forming properties of V-Ti-Ni shape memory alloy, ensuring the smooth progress of subsequent processes;

[0350] The melting process involves placing the prepared raw materials into a vacuum medium-frequency induction furnace for melting. During the melting process, the vacuum level must be strictly controlled at 1×10⁻⁶. -2 —1×10 -3 Between Pa, after all the raw materials have completely melted, argon gas is introduced into the furnace for protection to prevent the alloy from oxidizing at high temperatures. Then the molten alloy liquid is poured into ingots.

[0351] S5.1 Ingot stripping and trimming: Take out the ingot that has been cast after vacuum melting, and then use mechanical equipment to remove the oxide scale, inclusions and irregular parts of the surface of the ingot. Trim the size of the ingot to meet the specifications and shape required by the hot forging process, such as square or round billet, to avoid surface defects affecting subsequent processing.

[0352] The billet peeling and trimming process requires the complete removal of surface oxide scale and impurity layers to prevent them from affecting the subsequent forging structure and mechanical properties.

[0353] The billet is peeled and trimmed, and excessive heating or mechanical stress should be avoided during the trimming process to prevent surface cracks.

[0354] The billet peeling and trimming process requires controlling the trimming dimensional tolerances to ensure that the billet is heated evenly in the hot forging furnace.

[0355] S5.2 Ingot loading and heating: Place the trimmed ingot into the box furnace, set the heating program, gradually raise the temperature to between 800℃ and 950℃, and maintain this temperature range for 30-150 minutes.

[0356] During the furnace heating process of the billet, the heating rate should be controlled to prevent thermal stress cracks in the billet and to ensure uniform temperature distribution inside the furnace.

[0357] The process of loading and heating the billet into the furnace requires placing the trimmed billet into a box furnace and selecting a suitable support or tray to avoid direct contact between the billet and the furnace wall to prevent local overheating.

[0358] During the furnace heating process of the billet, the preheating stage should avoid rapid temperature rise that could cause an excessive internal temperature gradient, and the rate of temperature rise should be controlled appropriately to avoid thermal stress caused by thermal shock that could lead to billet cracks.

[0359] During the furnace heating process of the ingot blank, if a tin furnace heating curve is used, it is recommended to control it in segments to ensure uniform temperature at the center and surface of the ingot blank.

[0360] S5.3 Heat preservation treatment: The billet is heated to a set temperature of 800℃-950℃ and held for 30-150 minutes. Then, heat preservation is carried out to make the internal temperature of the alloy reach equilibrium, promote the homogenization of grains and eliminate internal stress.

[0361] The purpose of the heat preservation treatment is to maintain the temperature at a set temperature for a sufficient time to promote the homogenization of the internal grains of the alloy and the release of internal stress. After the heat preservation is completed, slow cooling or isothermal cooling can be selected according to the process requirements to avoid sudden cooling that could cause structural damage.

[0362] The heat preservation treatment is carried out for a sufficiently long time to achieve uniform microstructure and release internal stress, thereby reducing deformation resistance during subsequent hot forging.

[0363] The heat preservation treatment controls the atmosphere conditions (protective atmosphere or vacuum is recommended) to reduce high-temperature oxidation;

[0364] After the insulation treatment is completed, the temperature needs to be lowered slowly or at a constant rate according to the process requirements to avoid thermal stress regeneration.

[0365] S5.4 Billet Removal: After the heat preservation is completed, the billet is removed from the furnace quickly or slowly according to the process requirements, and is ready to enter the hot forging process. During the transfer process, violent collisions and stress concentrations should be avoided.

[0366] The removal of the ingot is a process that requires the use of special tools to handle high-temperature ingots, in order to prevent deformation and personnel safety risks.

[0367] The removal of the ingot needs to be arranged according to the hot forging time to ensure that the ingot temperature meets the requirements of the hot forging process.

[0368] S6. Hot forging: After heating is completed, hot forging is carried out, and the final forging temperature is controlled at 650-700℃ to obtain a square billet with a squareness of 30mm-60mm;

[0369] The purpose of hot forging is to shape the billet into a smaller square billet through the hot forging process, while adjusting the grain structure and improving the mechanical properties of V-Ti-Ni shape memory alloy.

[0370] The advantage of hot forging is that the hot forging process can significantly improve the plasticity and machinability of V-Ti-Ni shape memory alloys, providing a good foundation for subsequent rolling.

[0371] S6.1 Billet trimming: The obtained alloy billet is peeled and trimmed to remove surface defects, oxide layers, and mechanical damage, ensuring that the billet surface is flat and the dimensions meet the requirements of hot forging, and preventing surface defects from expanding during the hot forging process;

[0372] The billet trimming process requires the complete removal of defects on the alloy surface to prevent the defects from expanding and causing cracks during hot forging. High dimensional accuracy in billet trimming is necessary to ensure uniform heating of the billet in the furnace. At the same time, mechanical operation should avoid excessive cooling of the billet.

[0373] S6.2 Heating of billet before hot forging: The trimmed billet is placed in a box furnace for heating. The heating temperature is controlled between 800℃ and 950℃, and held at this temperature for 30 to 150 minutes to ensure uniform temperature inside and on the surface of the billet, thereby achieving homogenization of the microstructure and elimination of internal stress.

[0374] Before hot forging, the billet should be heated at a uniform rate to avoid temperature differences that could cause thermal stress. The holding time should be adjusted according to the billet size to ensure thorough heating and to maintain an inert atmosphere or good furnace temperature stability to reduce oxidation.

[0375] S6.3 Hot forging deformation: After heat treatment, the heat-treated billet is quickly transferred to the forging machine tool and hot forging is carried out immediately. The final forging temperature needs to be controlled between 650℃ and 700℃. The billet size is reduced by forging to obtain a square billet with a cross-sectional squareness of 30mm to 60mm, ensuring that the overall size of the forging is uniform and facilitating subsequent hot rolling.

[0376] The hot forging deformation requires maintaining the forging temperature within a suitable range to ensure good material plasticity and avoid the generation of hot or cold cracks.

[0377] The hot forging deformation is carried out with the forging speed controlled within the range of 5–20 mm / s and the forging pressure controlled within the range of 100–250 MPa to avoid surface roughness or structural damage of the forgings.

[0378] The hot forging deformation, with a deformation amount ≥30% reduction in cross-sectional area, promotes grain refinement and uniform microstructure, ensures that the billet obtains sufficient plastic deformation during hot forging, effectively promotes grain refinement and uniform microstructure, prevents surface roughness and crack formation, thereby improving the mechanical properties and subsequent processing adaptability of V-Ti-Ni shape memory alloy;

[0379] S6.4 Billet Cooling and Transfer: After hot forging, the forging is cooled or air-cooled according to the process requirements. After cooling to a safe temperature, it is transferred to the next process.

[0380] The cooling and transfer of the forgings require control of the cooling rate to prevent thermal stress from causing cracks or warping, and to avoid the generation of thermal stress and deformation defects.

[0381] The forgings are cooled and transported, and mechanical collision damage is prevented during the transport process. After being cooled to a safe temperature, they are transported to the next process for subsequent processing.

[0382] S7. First hot rolling: The hot-forged square billet is placed in a box furnace and heated at 800-950℃. After holding at this temperature for 30-120 minutes, it is hot rolled to obtain a rod billet with a diameter of 6mm-12mm.

[0383] The purpose of hot rolling is to further deform the square billet to produce a rod billet, and to control the size of the V-Ti-Ni shape memory alloy to be Φ6mm-Φ12mm.

[0384] The advantage of hot rolling is that the hot rolling process can further refine the grain structure of the alloy and improve the strength and toughness of V-Ti-Ni shape memory alloy.

[0385] S7.1 Heating of billet: The billet obtained in step (4) is placed back into the box furnace for heating. The heating temperature is also controlled between 800℃ and 950℃, and the holding time is 30 to 120 minutes.

[0386] The billet is heated at a rate of 5°C / minute to 15°C / minute to avoid excessive temperature gradients that could cause thermal stress. This is because a heating rate that is too fast (>15°C / minute) can easily lead to a large temperature difference between the surface and interior of the billet, generating thermal stress and causing cracks or warping. On the other hand, a heating rate that is too slow (<5°C / minute) will reduce production efficiency and is not conducive to process cycle control.

[0387] The billet heating and holding time is 30-120 minutes, which is adjusted according to the billet size and furnace temperature uniformity to ensure thorough heating. In actual production, the heating curve is adjusted according to the billet size and furnace type, and temperature sensors are used for real-time monitoring to ensure the heating process is safe and stable.

[0388] The billet is heated, and a protective atmosphere (such as argon) or a good seal inside the furnace can be used during the heating process to prevent oxidation.

[0389] S7.2 Rolling (Rod Billet): After heat preservation, the heat-preserved square billet is quickly transferred to the hot rolling mill for multiple hot rolling passes to roll the square billet into a rod billet with a diameter of Φ6mm-Φ12mm.

[0390] The rolling process controls the rolling speed and deformation to ensure uniform bar size and microstructure;

[0391] The rolling process is carried out at a rolling speed of 0.1–1.0 m / s to prevent surface cracks or internal defects caused by excessive speed.

[0392] In the rolling process, the deformation per pass is 10%–20%, the cumulative deformation should be ≥30%, and the total reduction should reach 30% or more to promote grain refinement.

[0393] During the rolling process, the temperature of the billet is maintained within the range of 850℃–950℃ to avoid brittle fracture caused by a sudden drop in temperature.

[0394] During the rolling process, the rolling equipment should have the ability to apply force evenly to prevent irregular cross-sectional shapes of the billet.

[0395] S7.3 Cooling and Inspection after Hot Rolling: After hot rolling, the bar blank is naturally cooled to room temperature, and the dimensions and surface quality of the bar blank are measured to ensure that there are no cracks, oxidation and other defects.

[0396] The cooling after hot rolling is carried out at a rate of 5°C / minute to 20°C / minute, and the cooling method is natural air cooling or slow air cooling to avoid internal stress or deformation caused by rapid cooling.

[0397] The inspection methods mainly include visual inspection, magnetic particle testing, and ultrasonic testing, which promptly detect surface and internal defects in the alloy to ensure the quality of subsequent processes.

[0398] S8. Second hot rolling: The rod billet after hot rolling in "S7. First hot rolling" is placed in a tube furnace and heated at 800-950℃. After holding at this temperature for 30-120 minutes, it is hot rolled to obtain wire with a diameter of Φ2mm-Φ3mm.

[0399] The purpose of re-rolling into wire is to process the billet into fine wire through further hot rolling process to meet the needs of different applications. This not only achieves precise control of dimensions, but also promotes grain refinement and microstructure homogenization through multi-pass plastic deformation, improving the ductility and processing performance of the alloy to meet the needs of high-precision applications.

[0400] The advantage of re-rolling into wire is that the wire has good ductility and processability, which can meet the requirements of high-precision applications;

[0401] S8.1 Rod billet heating: The obtained rod billet is placed in a tube furnace for heating. The heating temperature is still controlled between 800℃ and 950℃, and the holding time is 30 to 120 minutes to ensure that the internal and surface temperatures of the rod billet are uniform and achieve a full heat penetration effect.

[0402] The rod blank is heated at a rate of 5°C / min to 15°C / min to avoid excessive temperature gradients that could cause thermal stress and deformation.

[0403] The rod blank is heated in an atmosphere protected by a high-purity inert gas (such as argon) to maintain a stable atmosphere inside the furnace. It is best to use an inert gas protection to prevent surface oxidation.

[0404] The heating and holding time of the billet is 30-120 minutes, which is adjusted according to the billet size and furnace temperature uniformity to ensure thorough heating.

[0405] S8.2 Rolling: After the heat preservation is completed, the bar billet is quickly transferred to the hot rolling equipment for multiple hot rolling passes to further roll the bar billet into wire with a diameter of Φ2mm-Φ3mm;

[0406] During the rolling process, the rolling speed is controlled at 0.05-0.5 m / s, which helps to maintain a stable deformation state and avoid local stress concentration.

[0407] During the rolling process, the deformation per pass is maintained between 8% and 15%, which reduces the risk of mechanical damage and cracking during hot rolling.

[0408] During the rolling process, the cumulative reduction rate of multiple hot rolling passes is ≥30%, ensuring sufficient plastic deformation and effectively promoting dynamic recrystallization;

[0409] The hot rolling process maintains the temperature of the billet during the rolling process, with the rolling temperature range being 850℃-950℃, to prevent the material from becoming brittle due to a sudden drop in temperature. In addition, the rolling equipment must ensure uniform force application to avoid irregular cross-sections of the wire.

[0410] For the hot rolling process, the temperature control system should be able to control the temperature of the rolling zone within ±10℃ to ensure thermoplasticity;

[0411] The hot rolling process has a roll gap adjustment accuracy of ≤0.05mm to ensure uniform distribution of rolling force, prevent irregular deformation of the billet or wire cross-section, avoid uneven thickness and cross-sectional deformation, and improve rolling quality.

[0412] For the hot rolling process, the uniformity of the roll pressure should be within a variation range of ≤5%, and the hydraulic or mechanical pressure system should be kept stable to reduce product defects caused by pressure fluctuations.

[0413] S8.3 Wire Cooling and Quality Inspection: After hot rolling, the wire is naturally cooled to room temperature, and then the wire is dimensionally measured and surface quality is inspected to ensure that there are no cracks, oxidation and other defects, so as to ensure the product quality and performance stability of subsequent processing steps.

[0414] The cooling and inspection of the filaments shall be carried out with the cooling rate controlled between 5°C / minute and 20°C / minute. Natural air cooling or slow air cooling is preferred to ensure a uniform and stable cooling process and avoid thermal stress and structural deformation.

[0415] The cooling and inspection of the wire involves various non-destructive testing methods, such as visual inspection, magnetic particle testing, and ultrasonic testing, to promptly detect surface and internal defects and ensure the product quality and performance stability of subsequent processing steps.

[0416] S9. Cold drawing: The Φ2mm-Φ3mm wire obtained in step (6) is cold drawn according to the user's specific needs to obtain the memory alloy wire with the final required diameter;

[0417] The purpose of the cold drawing is to further adjust the diameter of the wire.

[0418] The advantage of cold drawing is that it can further improve the strength and dimensional accuracy of the wire, making it suitable for applications with high precision requirements.

[0419] S9.1 Wire preparation and surface cleaning: Take out the Φ2mm to Φ3mm wire obtained from the second hot rolling, perform surface cleaning, mechanical polishing, chemical cleaning or ultrasonic cleaning to remove surface oxides, oil and impurities, and ensure that the wire surface is smooth and defect-free during the drawing process;

[0420] The preparation and cleaning of the filaments must ensure that there are no residual impurities on the surface to prevent the filaments from being scratched or broken during the drawing process.

[0421] S9.2 Installation and parameter setting of drawing equipment: Assemble the cold drawing equipment, select a drawing die with the required diameter, accurately control the die hole diameter, and set reasonable drawing speed, drawing tension and lubrication conditions to ensure that the drawing process is smooth and the wire surface is not damaged.

[0422] The equipment installation and parameter settings, and precise control of the mold aperture, ensure dimensional consistency.

[0423] The equipment installation and parameter settings, and the reasonable control of the drawing speed, are designed to avoid wire breakage or surface damage.

[0424] The equipment installation and parameter settings, along with the selection of a suitable lubricant, reduce friction and protect the wire surface;

[0425] S9.3 Cold drawing operation: Pass the wire through the drawing die and gradually reduce the wire diameter to the user's requirements using a multi-segment or continuous drawing method;

[0426] The cold drawing operation requires real-time monitoring of drawing tension and speed to maintain a stable drawing process and prevent wire breakage or surface damage.

[0427] The cold drawing operation involves a drawing tension of 50-150 MPa. Excessive tension can cause the wire to break brittlely, while insufficient tension results in low drawing efficiency. The tension needs to be adjusted in combination with the equipment and material properties.

[0428] The cold drawing operation has a drawing speed of 0.5-3 m / min, that is, controlled between 0.5 and 3 meters per minute, to ensure uniform material deformation and reduce heat accumulation;

[0429] The cold drawing operation has a single reduction rate of 3%–8%, and small diameter changes help to control uniform deformation and prevent defects;

[0430] The cold drawing operation has a cumulative reduction rate of ≥15%, and the total deformation ensures performance improvement and dimensional stability.

[0431] During the cold drawing operation, the tension fluctuation is ≤5%, and the tension is kept stable to avoid uneven stress concentration during the processing.

[0432] S9.4 Finished Product Inspection and Packaging:

[0433] After cold drawing, the diameter of the wire is measured using a precision diameter gauge to ensure that the tolerance is controlled within ±0.01mm. Then, visual inspection and necessary non-destructive testing are carried out to confirm that there are no cracks, scratches and oxidation marks on the surface of the wire.

[0434] The finished product inspection and packaging process involves checking for cracks, scratches, or oxidation marks on the surface, followed by mechanical performance testing, such as tensile strength and hardness, to ensure that the design specifications are met.

[0435] The finished product inspection and packaging process involves packaging qualified products and labeling them with relevant specifications and batch information.

[0436] Example 2: Specific Implementation of the Preparation Method of the Present Invention Regarding "S1. Density Functional Theory (DFT) Calculation"

[0437] This invention discloses a high-vanadium (V) content V-Ti-Ni shape memory alloy and its preparation method. Through density functional theory (DFT) calculations, the influence of V doping on the performance of the Ti-Ni shape memory alloy is comprehensively analyzed, thus providing a theoretical basis for the design of high-performance Ti-Ni-V shape memory alloys. The DFT calculation steps in the preparation method described in this invention, by analyzing the alloy's electronic structure, mechanical properties, thermodynamic stability, and martensitic phase transformation, can optimize the alloy composition and production process, thereby improving the shape memory performance of the alloy at low temperatures.

[0438] This invention is the first to use density functional theory (DFT) to systematically and quantitatively calculate the role mechanism of V in Ti-Ni alloys. It clearly points out that within the range of 1%-5% (atomic percentage) V content, the phase transformation behavior of Ti-Ni alloys in low-temperature environments can be significantly improved, especially while maintaining high elastic modulus and hardness, effectively reducing the stress-induced martensitic phase transformation temperature. This optimization result is significantly different from traditional empirical design and provides practical basis for the development of low-temperature functional shape memory alloys.

[0439] The present invention discloses a high-vanadium (V) content V-Ti-Ni shape memory alloy and its preparation method. The specific steps of the "S1. Density Functional Theory (DFT) calculation" step, which uses density functional theory (DFT) to calculate the effect of vanadium (V) doping on the properties of the Ti-Ni shape memory alloy, are as follows:

[0440] S1.1 Establishing a crystal structure model: Based on the TiNi alloy with B2 structure, a 3×3×3 supercell model is constructed to ensure the accuracy of the doping ratio simulation. In addition, some atoms at Ti or Ni positions in the unit cell are systematically replaced with V atoms to construct simulation models with different doping ratios, such as 1%, 2%, 3%, 4%, 5%, 6%, 8%, and 10%.

[0441] S1.11 Selection of the parent crystal structure model: The B2 structure of the parent TiNi alloy is determined to be a cubic crystal with space group Pm-3m, and the standard unit cell parameter (a≈3.015Å) of this structure is obtained as the starting point;

[0442] S1.12 is extended to a supercell model: construct a larger supercell, such as a 3×3×3 B2 supercell containing 54 atoms;

[0443] The purpose of extending to a supercell model is to add different numbers of V atoms into a larger unit cell to accurately simulate the doping behavior of different atomic percentages and reduce the influence of periodic boundary effects on local structural perturbations.

[0444] S1.13 Doping Scheme Design and Modeling: For each doping ratio (e.g., 1%, 2%, ... 10%), perform the following steps:

[0445] S1.131 substitution method to introduce V atoms: According to the target doping ratio, equal amounts of Ti or Ni atoms are selected from the supercell in an ordered or random manner, and these atoms are replaced with V atoms. For example, in the 54-atom model, replacing 1 atom results in 1.85%, and replacing 2 atoms results in 3.7%.

[0446] The difference in performance caused by whether V replaces Ti or Ni atoms is significant. In V-Ti-Ni ternary alloys, different substitutions of V will result in significant differences in alloy properties, as detailed below:

[0447] The substitution method introduces V atoms, and by preferentially replacing Ti atoms with V, it is shown that the V-Ti-Ni ternary alloy of the present invention can more effectively reduce the stress-induced martensitic phase transformation temperature without significantly affecting mechanical properties, and is suitable for low-temperature functional scenarios, such as deep-sea exploration and materials for extremely cold environments.

[0448] S1.132 Constructing multiple sets of proportional models to account for statistical errors: Since different atomic substitution positions affect the energy results, it is necessary to construct multiple different configurations for each doping ratio, such as substituting different Ti atom positions or Ni atom positions; sometimes, a special quasi-random structure (SQS) is used to better simulate real random solid solutions.

[0449] S1.14 Preliminary Structure Optimization Preparation: Convert the format of the doped structure (such as POSCAR or CIF format) for DFT program input, then set the initial lattice parameters to keep the volume consistent with the original unit cell, in preparation for geometric optimization;

[0450] Verification of the S1.15 doping model: Check whether there are unreasonable atomic overlaps or atomic pairs with too small spacing in the model. Then use visualization tools (such as VESTA, OVITO) to check whether the lattice maintains the basic B2 configuration. If local structural instability is found, preliminary coarse optimization or adjustment of doping positions can be performed.

[0451] S1.2 Setting calculation parameters: DFT calculation was performed using VASP software, with GGA-PBE functional, energy cutoff set to 500eV, K-point grid set to 5×5×5, full structure relaxation was applied to minimize lattice energy (ion positions and lattice constants were optimized), and the vacuum layer was set to 15Å to eliminate periodic boundary effects and ensure minimum system energy.

[0452] The specific parameter values ​​and their order in the calculation settings are as follows:

[0453] S1.21 Selection of Exchange-Correlation Functional: The GGA (Generalized Gradient Approximation)-PBE (Perdew–Burke–Ernzerhof) functional is chosen for its suitability in describing transition intermetallic compounds and metallic bonded systems.

[0454] The purpose of using the exchange-correlation functional is to obtain more accurate predictions of the energy, volume, and elastic parameters of metallic systems, because the exchange-correlation functional predicts the lattice constant less accurately than the LDA functional.

[0455] S1.22 Energy Cutoff: Set the plane wave energy cutoff value (ENCUT) to 500 eV;

[0456] The purpose of setting the energy cutoff is that the energy cutoff determines the upper limit of the expansion of the plane wave basis function, which should be higher than the maximum recommended value of all elements, that is, the PAW potential energy file of V, Ti, and Ni is ≥450eV. If higher accuracy is required, convergence can be further tested between ENCUT=450-600eV for convergence judgment.

[0457] S1.23 Set K-Point Mesh: Use the Monkhorst-Pack format for K-point sampling in the first Brillouin zone, set a 5×5×5 K-point mesh as the supercell to ensure sufficient k-space sampling;

[0458] The purpose of setting the K-point grid is that, for a 54-atom supercell structure, this K-point density can ensure the accuracy of structural relaxation and band structure calculation within a reasonable time.

[0459] S1.24 Enables structural relaxation:

[0460] Set IBRION=2 (conjugate gradient method) or 1 (quasi-Newton method).

[0461] Setting ISIF=3 allows for optimization of atomic positions, lattice constants, and unit cell shapes.

[0462] Set the maximum force convergence criterion: EDIFFG = -0.02 eV / Å, that is, stop optimization when the maximum atomic force is < 0.02 eV / Å.

[0463] The optimization objective is to obtain a stable structure with the lowest energy state;

[0464] S1.25 sets the convergence criteria:

[0465] The electron energy convergence criterion (EDIFF) is set to 1×10. -5 eV, ensuring that the energy change during the self-consistent field (SCF) calculation process is small enough.

[0466] Set the maximum number of iterations to NELM=100 to prevent SCF from failing to converge;

[0467] Enable precise charge density integration options (such as PREC=Accurate) to improve the accuracy of subsequent DOS calculations;

[0468] S1.3 Doping Scheme Design and Modeling: Calculate the total energy (E) for each doping ratio model. total ), elastic constant (C) 11 C 12 C 44 The shear modulus and Young's modulus were derived, and their mechanical properties were evaluated. At the same time, the energy difference ΔE of the B2→B19' phase transformation of the doped system was calculated, and the trend of its stress-induced martensitic phase transformation temperature was predicted.

[0469] The purpose of the doping scheme design and modeling is to determine how to construct models with different doping ratios and how to consider the statistics of atomic arrangement in first-principles (DFT) simulations. This will directly determine whether your subsequent energy, structure, and electronic performance calculations are true and reliable.

[0470] S1.31 Calculate and determine the number of replacement atoms for the target doping ratio: Based on the constructed supercell, such as 3×3×3B2-TiNi, containing 54 atoms, determine the number of replacement atoms required for each doping ratio:

[0471] The calculation and determination of the number of replacement atoms at the target doping ratio should avoid excessive replacements that could lead to severe lattice distortion or the formation of a local second phase structure.

[0472] S1.32 Design replacement method and doping element site occupation strategy: Clearly define the replacement object, that is, V is preferred to replace Ti atoms, as Ti site replacement is better for structural stability as mentioned above;

[0473] The design replacement method and dopant element occupancy strategy can be selected as follows:

[0474] Ordered substitution, that is, preferential selection of Ti atoms with symmetrical positions or similar local environments in the unit cell;

[0475] Random replacement, that is, randomly selecting multiple Ti atom configurations to avoid biased structures;

[0476] A hybrid strategy, namely partial substitution of Ti and partial substitution of Ni, was used to compare the effects of substitution mechanisms.

[0477] S1.33 Construct multiple different configuration models (redundant configurations): For the same doping ratio, such as 2 atoms = 3.70%, construct multiple different substitution combination models, and use each configuration for independent calculations to compare the differences in performance such as total energy and lattice parameters, and evaluate statistical errors.

[0478] For example, replace the Ti atom numbers A+B, C+D, E+F, etc., and then perform independent calculations for each configuration.

[0479] S1.34 Constructing a special quasi-random structure (SQS) model: When it is necessary to simulate the doping behavior of real solid solutions, especially when high concentration doping or when the desired structure is statistically averaged, the SQS method is introduced, and then the ATAT and mcsqs programs are used to generate special structures equivalent to random doping distributions.

[0480] The purpose of constructing the Special Quasi-Random Structure (SQS) model is to more accurately reproduce the distribution pattern of V atoms in the microstructure of the raw material and reduce the number of models.

[0481] S1.35 Structure Check and Pre-optimization: Use visualization software (such as VESTA, OVITO) to check the structure of each configuration model: whether there is atomic overlap; whether abnormal lattice is formed around the replaced atoms; if the local structure is unstable, a fast coarse optimization can be performed to eliminate the initial lattice stress.

[0482] S1.4 Performance Trend Analysis: Summarize the effects of different doping ratios on mechanical properties, martensitic phase transformation tendency, and electronic structure properties, and further identify that within the range of 1%-5%V content, both Ti-Ni memory properties can be maintained and the stress-induced martensitic phase transformation temperature can be significantly reduced.

[0483] S1.41 Model Format Conversion: Use modeling software (such as Materials Studio, VESTA, ASE) to export the doped structure model to a standard format:

[0484] The format of the VASP is POSCAR (atomic coordinates + lattice constant).

[0485] The QuantumESPRESSO is in CIF / pw.in format.

[0486] The CASTEP file is in .cell / .param format.

[0487] The purpose of the model format conversion is to ensure that the coordinate units are correct (fractional coordinates vs. Cartesian coordinates), the atomic order is consistent with the pseudopotential file, and the positions of the replaced V atoms are clearly marked;

[0488] S1.42 Set initial lattice parameters: The default lattice parameters of the TiNi matrix are used as the initial values ​​(e.g., a≈3.015Å for B2 structure). Then, when constructing the supercell (e.g., 3×3×3), the lattice is enlarged synchronously. If the V replacement ratio is high (>5%), the lattice parameters can be fine-tuned to avoid excessive distortion of the original lattice, but volume optimization is not performed first in order to evaluate the pure doping effect.

[0489] S1.43 Constructing a complete DFT input file: Inputting the data for VASP series software:

[0490] The POSCAR contains lattice parameters and atomic coordinates.

[0491] The INCAR parameter specifies the calculation type (structural optimization) and accuracy parameters.

[0492] KPOINTS: Brillouin zone sampling grid, such as 5×5×5.

[0493] The POTCAR file contains PAW pseudopotential files for Ti, Ni, and V.

[0494] Then check whether the structure can be correctly parsed by preprocessing scripts (such as vaspkit, pymatgen checking tools);

[0495] S1.44 Automatic annotation and model tagging: Used for batch calculations, it adds a unique ID to each model structure and then reflects the doping information and atomic positions in the POSCAR annotation line or output folder name, which facilitates batch calculations and result tracking;

[0496] S1.45 Check and correct atomic spacing anomalies or structural distortions: Use structural visualization software (VESTA, OVITO) or scripts (such as ASE, pymatgen) to check:

[0497] Does it involve unreasonable interatomic spacing, such as <1.8 Å or >4.5 Å?

[0498] Whether there are duplicate atoms, missing atoms, or a shift in the center of gravity.

[0499] If an anomaly is found, perform rapid structural pre-optimization or fine-tune the coordinates;

[0500] S1.5 Conclusion Output: It is recommended that the V content be controlled within the range of 1%-5% atomic percentage to provide a quantitative reference for subsequent component design;

[0501] S1.51 Summary of Calculation Results: The model calculation results for each doping ratio (e.g., 1.85%, 3.7%, 5.6%, 7.4%, 9.3%) are summarized, including:

[0502] The total energy (E) total );

[0503] The martensitic phase transformation energy barrier (ΔE) B2→B19' );

[0504] The elastic constant (C) 11 C 12 C 44 );

[0505] The derived mechanical parameters (shear modulus G, bulk modulus B, Young's modulus E).

[0506] The charge density map / density of states (DOS) is described.

[0507] The results are displayed using tables or graphs, such as ΔE-V content curves or modulus-V content line graphs.

[0508] S1.52 performance change trend comparative analysis:

[0509] S1.521 analyzes the functional relationship between the doping ratio and performance parameters:

[0510] Does ΔE continuously decrease as the V content increases?

[0511] Within which doping ratio ranges does the mechanical property (modulus) remain stable?

[0512] Does the lattice stability exhibit a sudden inflection point?

[0513] S1.522 then searches for the optimal doping window based on performance, for example:

[0514] The ΔE decreases linearly from 1% to 5%;

[0515] More than 5% of the structure is unstable or its performance is degraded;

[0516] Therefore, a vanadium content of 1%-5% is determined to be the recommended range for the performance of Ti-Ni shape memory alloys.

[0517] S1.53 Determining Material Suitability:

[0518] S1.531 Low Temperature Judgment: Determine whether the doped V-Ti-Ni alloy meets the following basic requirements for functional materials used at low temperatures:

[0519] The sufficiently low phase transition temperature (ΔE decreases);

[0520] The original Ti-Ni memory properties (modulus and B2 structure stability) are maintained.

[0521] No serious structural defects or electronic structure damage were introduced.

[0522] S1.532 Determining the application area of ​​the alloy: If the above conditions are met, it can be determined that the alloy is suitable for:

[0523] Whether the alloy can adapt to deep-sea exploration (low temperature and high pressure);

[0524] Whether the alloy can adapt to the thermal control structure of the spacecraft (low-temperature environment reactive structure).

[0525] Whether the alloy can be adapted to polar engineering materials.

[0526] S1.54 Quantitative Sizing Recommendations: The recommended doping ratios are compiled into a sizing chart or recommendation table, as follows:

[0527] The conclusion drawn from the quantitative proportioning recommendations is that the V content should be controlled between 1% and 5% (atomic percentage) to replace Ti atoms, which can achieve low-temperature phase transition regulation without reducing the structure and mechanical properties.

[0528] S1.55 composition design provides input parameters: the recommended doping range is fed back to the "S2.V-Ti-Ni composition design" step as the atomic ratio input for actual batching; at the same time, it can guide the melting ratio (V atomic mass, converted to g / batch), realizing a closed loop between theoretical calculation and engineering preparation.

[0529] Based on the specific steps described above, and through the specific implementation of the "S1. Density Functional Theory (DFT) calculation" in the preparation method of a high vanadium V-content V-Ti-Ni shape memory alloy of the present invention, the results obtained are as follows:

[0530] First, the optimal range for V doping was quantitatively determined. Through density functional theory (DFT) simulations, the structural energy, phase transformation behavior, and mechanical modulus of Ti-Ni alloys were calculated at different doping ratios (1%-10%). It was clearly shown that when the V content is controlled within the range of 1%-5% (atomic percentage), the stress-induced martensitic phase transformation temperature (ΔE decrease) can be significantly reduced; at the same time, the structural stability and mechanical properties of the alloy, such as shear modulus, bulk modulus, and lattice constant fluctuations, are maintained within 5%.

[0531] Second, it is explicitly recommended to replace Ti sites with V instead of Ni. Replacing Ti atoms can introduce reasonable stress perturbations within the crystal lattice, which is conducive to the B2→B19' phase transition, but does not destroy the basic B2 configuration; although replacing Ni atoms can lower the temperature, it causes electronic structure disorder and a decrease in crystal stability, which is not conducive to industrially controllable preparation.

[0532] Third, the recommended atomic ratio is output. The recommended ratio of a V-Ti-Ni shape memory alloy with high vanadium (V) content in this invention is: vanadium (V) content of 1%-5% (atomic percentage), Ti:Ni = 49.3:50.7.

[0533] Therefore, this invention, through first-principles calculations, clearly indicates that the preferred doping range for V in Ti-Ni shape memory alloys is 1%-5% (atomic percentage), with Ti sites being the recommended doping sites, forming a V-Ti-Ni ternary system. Within this doping range, the alloy maintains good mechanical properties and structural stability while effectively reducing the martensitic phase transformation energy barrier, making it suitable for applications requiring special shape memory performance in low-temperature environments. This theoretical design provides a quantitative basis and scientific support for subsequent alloy proportioning design, smelting preparation, and the development of low-temperature shape memory alloys.

[0534] The specific implementation of "S1. Density Functional Theory (DFT) calculation" in the preparation method of a high vanadium (V) content V-Ti-Ni shape memory alloy described in this invention has the following significance for the overall technical solution:

[0535] First, it realizes the transformation from "blind doping" to "precise alloy design". That is, this step guides alloy design through DFT quantitative analysis, which greatly reduces experimental costs and failure rate.

[0536] Second, it provides a scientific starting point for the design of V-Ti-Ni low-temperature shape memory alloys. The result of "S1. Density Functional Theory (DFT) calculation" provides a clear target composition for subsequent steps S2.-S7. (batching, melting, and hot processing), avoiding abnormal material phase transformation or unstable structure caused by "unreasonable composition" in subsequent processing.

[0537] Third, the performance regulation logic supporting this invention in "low-temperature application scenarios", namely the "S1. Density Functional Theory (DFT) calculation" design directly targets the problem of "stress-induced martensitic phase transformation temperature" regulation, which is the fundamental mechanism for realizing low-temperature responsive alloys, making this technical solution patentable and industrially applicable.

[0538] Example 3: Specific Implementation of the Preparation Method of the S2.V-Ti-Ni Shape Memory Alloy in this Invention

[0539] The present invention discloses a high vanadium (V) content V-Ti-Ni shape memory alloy and its preparation method. The specific implementation of "S2. Composition design of V-Ti-Ni shape memory alloy" plays a key role in ensuring the stability of material quality, the controllability of alloy ratio, and the compatibility of subsequent batch preparation processes in the actual technical solution.

[0540] The present invention discloses a high-vanadium (V) content V-Ti-Ni shape memory alloy and its preparation method. The specific steps of "S2. Composition design of V-Ti-Ni shape memory alloy" are as follows:

[0541] Compositional Design Steps for S2.V-Ti-Ni Shape Memory Alloy

[0542] S2.1 Determine the types and sources of elements: Determine the element selection for V-Ti-Ni shape memory alloy, specifically vanadium (V), titanium (Ti), and nickel (Ni); then determine the raw material sources for V-Ti-Ni shape memory alloy: commercially available sponge titanium (purity ≥99.9%), high-purity nickel (purity ≥99.9%), and self-made vanadium-nickel alloy (V-Ni pre-alloy).

[0543] S2.11 Determine the elemental composition of the alloy system: Based on the theoretical design results in S1, it is clear that the present invention adopts a ternary alloy system of vanadium (V), titanium (Ti), and nickel (Ni): V-Ti-Ni; wherein: titanium (Ti) and nickel (Ni) are the basic elements of shape memory alloys, while vanadium (V) is a functional control element used to lower the martensitic phase transformation temperature;

[0544] S2.12 Analyze the technical function of each element:

[0545] The technical function of titanium (Ti) is that it is the main element constituting the cubic B2 matrix phase, influencing elasticity and structural transformation.

[0546] The technical function of nickel (Ni) is to regulate the stability of the TiNi phase, which is key to maintaining its shape memory properties.

[0547] The technical function of vanadium (V) is to adjust the elastic distortion and martensitic phase transformation threshold of crystals through substitutional doping, and it is a functional additive element.

[0548] S2.13 Determination of Raw Material Purity and Source: To ensure the stability of the final V-Ti-Ni shape memory alloy's alloy properties, high-purity metallic materials must be selected. Specific sources are as follows:

[0549] Therefore, the purity and source of the raw materials are determined, indicating that since V is easily oxidized or evaporated during high-temperature smelting, the use of pre-alloyed V-Ni alloy can significantly improve smelting stability and doping ratio control accuracy.

[0550] S2.14 Verify the compatibility of raw materials with existing process platforms: Assess whether the selected Ti, Ni, and V-Ni alloys are compatible with existing vacuum induction melting equipment, and then check their coefficient of thermal expansion, melting point, and physical morphology to ensure that they are suitable for simultaneous melting and thorough mixing, thereby ensuring that refractory inclusions or interface reaction problems are not introduced.

[0551] S2.15 Establish weighing accuracy control specifications: For raw materials with high purity but large density differences (such as Ti being light and Ni being heavy), establish weighing and mixing accuracy requirements (such as ±0.01g), and then establish raw material receiving acceptance and composition verification specifications in advance to ensure consistency between batches.

[0552] S2.2 Atomic ratio setting: V content is set to 1%-5% (atomic percentage), Ti:Ni=49.3:50.7 (atomic percentage), and the alloy as a whole is a ternary V-Ti-Ni system;

[0553] The setting of the atomic ratio of the elements is a key step in the transition from theoretical design to actual smelting. Its goal is to convert the doping ratio recommended by the "S1. Density Functional Theory (DFT) calculation" into specific and executable alloy composition parameters, and to provide a precise basis for subsequent material weighing and batching.

[0554] The atomic ratio setting of the elements is intended to reflect the technical basis of the ratio setting, the rationality of the doping window selection, the synergy with the ratio of the master alloy, and the preparatory work for how to convert from "atomic ratio" to "mass ratio".

[0555] S2.21 Confirmation of the ternary alloy system structure: It is determined that the system used in this invention is a ternary alloy V-Ti-Ni, and the V-Ti-Ni shape memory alloy composition must meet the following three constraints:

[0556] The sum of the total atomic percentages is 100%.

[0557] The Ti:Ni atomic ratio is fixed at 49.3:50.7.

[0558] The vanadium V is a substitute dopant, and the proportion varies between 1% and 5%.

[0559] S2.22 Define the V content range and construct the ratio matrix: Based on the theoretical analysis results of “S1. Density Functional Theory (DFT) Calculation”, the atomic percentages of vanadium V are selected as 1%, 3%, and 5% as typical doping points;

[0560] The process involves setting a V content range and constructing a ratio matrix. For each V ratio, the ratio of Ti to Ni is readjusted to maintain a total of 100%, as detailed below:

[0561] The process involves setting a V content range and constructing a ratio matrix. When V replaces Ti or Ni, in order to maintain the core performance structure of Ti:Ni≈49.3:50.7, it is necessary to compress Ti and Ni proportionally to ensure that the ternary ratio always maintains a stable transition.

[0562] S2.23 alloy composition ratio conversion (taking 100g as an example): According to the set atomic percentage, calculate the mass ratio of each element through molar mass, and then accurately weigh each element raw material (or pre-alloy) for experiment or batch preparation.

[0563] S2.231 Obtain the atomic masses (approximately) of the three elements: For the alloy described in this invention, V: 50.94 g / mol, Ti: 47.87 g / mol, Ni: 58.69 g / mol;

[0564] S2.232 is converted using a formula (example: based on 100 atoms):

[0565] Mass (element) = Atomic percentage × Atomic mass

[0566] For example, V=3%, Ti=47.821%, Ni=49.179%.

[0567] m V =3 × 50.94 = 152.82

[0568] m Ti =47.821×47.87≈2290.06

[0569] m Ni =49.179 × 58.69 ≈ 2886.33

[0570] Total mass = 5329.21

[0571] The final mass percentage of each element is:

[0572] S2.24 Establish a proportioning template for material weighing guidance: Generate a table of doping ratio and material mass (taking 100g as an example), and then scale it up proportionally when applying it to actual batches, such as when preparing a 500g sample, the mass of all elements is multiplied by 5;

[0573] S2.25 Verify consistency between the mix proportions and the theoretical model: Ensure that the design mix proportions are consistent with the DFT modeling structure in S1. If the modeling uses a Ti-substitute scheme, the actual preparation should also be calculated according to the V-substitute Ti allocation method.

[0574] S2.3 alloy composition ratio conversion (taking 100g as an example): According to the set atomic percentage, calculate the mass ratio of each element through molar mass, and then accurately weigh each element raw material (or pre-alloy) for experiment or batch preparation.

[0575] The alloy composition ratio conversion (taking 100g as an example) is a key operational step that ultimately translates the theoretical atomic percentage into the actual weighing and mixing ratio, serving as a bridge from "model design" to "experimental preparation".

[0576] The alloy composition ratio conversion involves not only mathematical conversion, but also reasonable unit conversion, material weighing process arrangement, error control, and special processing strategies for pre-alloyed (such as V-Ni) materials.

[0577] S2.31 Obtain the relative atomic mass of each element: Refer to the International Standard Atomic Weights Table to obtain the atomic masses (unit: g / mol) of the three metals, as follows:

[0578] S2.32 sets the atomic percentage composition: taking a doping ratio of 3% as an example:

[0579] The specified atomic percentage composition has a total atomic percentage of 100%, a Ti:Ni ratio of 49.3:50.7, and V is the doping ratio;

[0580] S2.33 Calculate the total molar mass of each element ( The formula is as follows:

[0581] Quality fraction i =

[0582] Vanadium (V): 3.0 × 50.94 = 152.82

[0583] Titanium (Ti): 47.821 × 47.87 ≈ 2290.06

[0584] NickelNi: 49.179×58.69≈2886.33

[0585] Total mass (theoretical molar weighted sum) ≈ 5329.21

[0586] S2.34 is converted to mass percentage:

[0587] Vanadium V mass percentage = ≈2.87%

[0588] Titanium (Ti) mass percentage = ≈42.96%

[0589] Nickel (Ni) mass percentage = ≈54.17%

[0590] S2.35 Calculate the weighing value based on the target total amount (e.g., 100g): Assuming the planned total smelting mass is 100g, then:

[0591] When calculating the mass percentage, please note the following:

[0592] If a V-Ni vanadium-nickel pre-alloy (e.g., V:Ni=1:2) is used to replace V and part of Ni, then the calculation needs to be done separately. For example, the amount of V-Ni pre-alloy added is equivalent to providing 2.87g of V, requiring: V: 2.87g; Ni: 2×2.87=5.74g; then subtract 5.74g from the Ni weighing, and the amount of pure Ni added alone is only 54.17–5.74=48.43g.

[0593] S2.36 Establish a weighing error control range: It is recommended to control the weighing error within ±0.01g, use an analytical balance to weigh accurately, and record the batch number and weighing data of the ingredients to form a traceability table.

[0594] S2.4 Mixing method design: Use a mechanical mixer to mix pre-alloyed powders in an inert atmosphere to ensure uniformity, or mix Ti raw materials in vanadium-nickel alloy pre-melt to achieve premixing;

[0595] The purpose of the aforementioned mixing method is to facilitate a critical transition from theoretical proportioning to physical batching operations. Its goal is to ensure that the ternary alloy raw materials have uniform composition, reasonable particle distribution, and effective oxidation control before mixing, thereby providing a stable mixing quality foundation for subsequent smelting.

[0596] The design of the mixing method involves not only the selection of mixing equipment, but also multiple process elements such as atmosphere control, particle size control, and mixing time optimization.

[0597] S2.41 Determine the hybrid strategy type: Based on the different ways of introducing V, there are two strategies:

[0598] Method A (conventional mixing of three metal powders): applicable when V, Ti, and Ni are added in elemental powder or small particle form.

[0599] Method B (vanadium-nickel pre-alloyed mixing): Applicable to V and Ni that have been melted into V-Ni pre-alloyed blocks (or powder), and only mixed with Ti.

[0600] Recommended method B is more suitable for the controlled mixing of elements (V) that are easily oxidized at high temperatures;

[0601] S2.42 Equipment and Environment Selection: Planetary ball mills, V-type mixers, vertical mixing tanks, etc., will be used, depending on the scale of the experiment. The mixing process will then be arranged in one of the following two types of environments:

[0602] Mix in an inert atmosphere (such as high-purity argon) protective box, or mix in a vacuum drying oven and then quickly seal for later use;

[0603] If not operated in a protective atmosphere, it should be operated in an environment with a relative humidity of ≤5% to avoid oxidation reaction;

[0604] S2.43 Setting Mixing Parameters: Based on the raw material particle size and batch size, set the following specific parameters:

[0605] The aforementioned mixing parameters, when the pre-alloy is in block form, require pre-crushing (mechanical crushing or ball milling) to ≤2mm particles.

[0606] The setting of mixing parameters requires screening of raw materials to ensure uniform particle size and improve mixing uniformity;

[0607] S2.44 Mixing uniformity test: Take samples from different locations (top, middle, bottom) of the mixed sample, and then use energy dispersive spectroscopy (EDS) or scanning electron microscopy (SEM) to analyze the composition distribution of the sample. If the elemental deviation is greater than ±3%, the mixing time should be extended or the particle size difference should be adjusted.

[0608] S2.45 Mixture Packaging and Labelling: Pack the uniformly mixed metal powder or granular mixture into a sealed stainless steel can or vacuum bag and affix a label indicating the alloy system (V-Ti-Ni), batch number, element ratio (mass percentage), mixing date and operator, and whether it is a pre-alloyed system (such as containing V-Ni pre-alloy).

[0609] S2.5 Recommendations for subsequent smelting parameters: Smelting should be carried out using a vacuum induction furnace, with the vacuum level controlled at 1×10⁻⁶. -2 —1×10 -3 Pa, the melt is cast into shape under argon protection to avoid oxidation;

[0610] The formulation of subsequent melting parameter recommendations involves multiple sub-operational steps, including equipment parameter setting, heating and holding process control, atmosphere conversion strategy, and casting mold design.

[0611] The purpose of formulating subsequent melting parameter recommendations is to transform the previously mixed V-Ti-Ni shape memory alloy into an initial alloy ingot, which is a key step and the first hot working process in the entire process chain.

[0612] The main goal of formulating the subsequent smelting parameter recommendations is to achieve a raw ingot with uniform composition, dense structure, and low oxygen inclusions, so as to provide an ideal structural basis for subsequent hot forging, hot rolling and other forming processes.

[0613] S2.51 Selection of smelting equipment and charging method:

[0614] The S2.511 smelting equipment selected is a vacuum induction furnace (VIM).

[0615] S2.512 Charging method: First, load the mixed alloy raw materials into a graphite crucible or alumina crucible. If it is a V-Ni pre-alloy + Ti scheme, it is recommended to place the V-Ni alloy at the bottom and cover it with Ti. Also, control the charging amount to ≤ 2 / 3 of the furnace cavity volume to prevent molten splashing or overflow.

[0616] S2.52 Vacuuming and Preheating: Start the vacuum system and control the vacuum level to 1×10⁻⁶. -2 —1×10 -3 Pa, and maintain the vacuum for 5-10 minutes to remove oxygen and water vapor from the cavity. Set the medium-frequency induction heating power to gradually increase mode to avoid sudden temperature changes that cause powder to fly. The initial power is 30%, and the temperature rises by 50-100℃ per minute. When it reaches 900℃, it enters the full power heating range. At this time, titanium (Ti) begins to melt, and vanadium (V) is half melted.

[0617] S2.53 Full Melt Heating and Melt Homogenization Treatment:

[0618] The full-melting heating and melt homogenization treatment raises the temperature to the fully molten zone at 1300-1450℃, and the melting time is controlled at 10-15 minutes;

[0619] The full melting heating and melt homogenization treatment uses an induction magnetic field stirring effect for industrial-grade applications or a mechanical stirring rod for experimental-grade applications, and holds the temperature for 3-5 minutes to ensure that the alloy composition is fully homogenized.

[0620] S2.54 Atmosphere Switching and Protective Casting: After the melt stabilizes, high-purity argon gas (purity ≥99.999%) is introduced to form a positive pressure protective atmosphere of 0.1-0.3MPa. Then, the lower valve is opened or the melt is poured into a metal mold or graphite mold. The mold needs to be preheated to 150-300℃ to avoid rapid cooling and cracking of the melt. During this process, the casting speed and thickness are controlled to ensure dense crystallization and no gas trapping.

[0621] S2.55 Cooling, Ingot Removal and Post-processing: Cool naturally to room temperature, remove the initial alloy ingot, weigh and number it, and record the smelting parameters (date, furnace number, actual temperature). If there are obvious shrinkage cavities, segregation, or inclusions, a second smelting (remelting) can be performed.

[0622] Based on the specific steps described above, and through the specific implementation of "S2. Compositional Design of V-Ti-Ni Shape Memory Alloy" in the preparation method of a high vanadium (V) content V-Ti-Ni shape memory alloy of the present invention, the results obtained are as follows:

[0623] Firstly, a V-Ti-Ni ternary shape memory alloy system with precise composition, strong thermal compatibility, and adjustable low-temperature response performance was constructed. The "S2. Composition Design of V-Ti-Ni Shape Memory Alloy" successfully designed a ternary alloy system based on the TiNi system and doped with V, controlling the V content within the 1%-5% atomic percentage range to achieve precise control of the martensitic phase transformation temperature; maintaining the core structural ratio of Ti:Ni≈49.3:50.7 ensures no loss of shape memory performance; the overall composition of the V-Ti-Ni shape memory alloy is scientific and balanced, meeting the microstructural requirements of shape memory functional materials.

[0624] Secondly, a quantitative proportioning scheme that can be converted into practical preparation was obtained, laying a good compositional and structural uniformity foundation for subsequent hot forging, hot rolling, and cold forming. The "Compositional Design of S2.V-Ti-Ni Shape Memory Alloy" successfully converted atomic percentages into mass percentages through molar mass calculations. Furthermore, taking 100g as an example, a proportioning template with a clear weighing range and stable ratio for each element was obtained, facilitating direct material feeding. Regarding the introduction of V, a V-Ni pre-alloy was used to replace part of the Ni and V powders, effectively improving the uniformity of doping and reaction stability during melting, and solving the problem of V's easy volatilization and oxidation.

[0625] Thirdly, an industrially applicable batching and mixing process route has been established, providing process support and mass production for the application of V-Ti-Ni based alloys in functional material scenarios such as deep-sea exploration, cryogenic equipment, and aerospace structures. "S2. Composition Design of V-Ti-Ni Shape Memory Alloys" has developed a mechanical mixing process scheme suitable for both laboratory and pilot-scale platforms, including the selection of mixing equipment, inert atmosphere control, particle size standards, and mixing time. It also provides a premixing scheme for V-Ni alloys and Ti, providing a highly consistent raw material foundation for subsequent batch melting.

[0626] Thirdly, it provides recommendations for melting parameters compatible with existing equipment. The "Compositional Design of S2.V-Ti-Ni Shape Memory Alloys" proposes an operating window for the vacuum induction furnace, including a vacuum level of 1×10⁻⁶. -2 —1×10 -3 The process involves casting at a Pa and a melting temperature of 1300-1450℃ under argon protection to ensure low oxygen levels and a dense microstructure in the alloy ingot. The melting process is compatible with existing TiNi melting lines, requiring no additional equipment investment, and offers excellent scalability and cost control advantages.

[0627] Through the systematic implementation of the "Composition Design of S2.V-Ti-Ni Shape Memory Alloy" described in this invention, precise control of the composition and seamless integration of process operability for V-Ti-Ni ternary shape memory alloys have been successfully achieved. This design scheme not only possesses rigorous theoretical basis but also incorporates actual material sources, batching methods, and melting parameters to construct a complete chain solution from theoretical prediction to mass production. The results provide a fundamental guarantee for the development of low-temperature responsive, mass-producible high-vanadium shape memory alloys, and are of great significance for promoting the application of shape memory alloys in deep-sea, extremely cold, and space structures.

[0628] The specific implementation of "S2. Compositional Design of V-Ti-Ni Shape Memory Alloy" in the preparation method of a high vanadium (V) content V-Ti-Ni shape memory alloy described in this invention has the following significance for the overall technical solution:

[0629] First, it achieves a precise transition from theoretical design to actual fabrication. The "Compositional Design of S2.V-Ti-Ni Shape Memory Alloy" transforms the recommended doping range (1%-5%V) calculated by density functional theory (DFT) into specific atomic ratios and mass proportions, thereby constructing a ternary alloy system (V-Ti-Ni) with precise and controllable composition, clear source, and stable quality. This successfully establishes a complete chain from "model → batching system → material entity," thus enabling the V-Ti-Ni shape memory alloy described in this invention to not only have a scientific basis but also practical manufacturing capabilities, enhancing the feasibility of the patent.

[0630] Secondly, it ensures the dual stability of the V-Ti-Ni shape memory alloy's structure and performance. The "S2. Composition Design of V-Ti-Ni Shape Memory Alloy" uses a standard atomic ratio framework of Ti:Ni = 49.3:50.7 as the main structural guarantee, ensuring that V doping does not disrupt the original TiNi shape memory effect. The proportion of V added is precisely controlled, and through mass conversion and batch calibration, problems such as uncontrolled doping, local segregation, or phase transformation failure are effectively prevented. This results in a V-Ti-Ni shape memory alloy with high stability, high purity, and consistent composition, providing a structural foundation for subsequent shape memory functions.

[0631] Third, the method of introducing V element has been optimized to solve the bottleneck of industrial application. The "Composition Design of S2.V-Ti-Ni Shape Memory Alloy" clearly adopts vanadium-nickel pre-alloying (V-Ni) instead of the direct introduction of metallic vanadium powder, avoiding the problems of easy oxidation and difficulty in uniformity of V in traditional processes. Combined with mechanical mixing or pre-melting treatment of Ti powder or Ti particles, it ensures effective doping of V element and batch-to-batch uniformity. The preparation method described in this invention has good industrial scalability, is compatible with conventional TiNi production lines, and requires no additional equipment.

[0632] Fourth, a standardized, low-pollution, and easily scalable batching and smelting process has been established. The "Composition Design of S2.V-Ti-Ni Shape Memory Alloy" has formulated strict and reproducible process parameter standards in terms of mixing environment (inert atmosphere), mixing time, particle size control, and proportioning accuracy. Furthermore, a complete parameter system has been set for the smelting stage, including vacuum degree, temperature, heat preservation, argon protection, and casting method. This has formed a green, safe, and batch-controllable preparation path for high vanadium content V-Ti-Ni shape memory alloys, promoting the engineering application of this material towards large-scale production.

[0633] Fifth, it provides a V-Ti-Ni shape memory alloy material solution for the development of low-temperature responsive materials. The V-Ti-Ni shape memory alloy prepared under the "S2. Composition Design of V-Ti-Ni Shape Memory Alloy" scheme has an adjustable martensitic phase transformation temperature, stable memory performance, and good hot working adaptability. It is suitable for applications with special requirements for low-temperature deformation response performance, such as deep-sea engineering, spacecraft temperature control structures, and extreme cold environment drive systems.

[0634] Example 4: Preparation and heat treatment process of V-Ti-Ni shape memory alloy wire with 2 at% vanadium content according to the preparation method of the present invention.

[0635] The preparation and heat treatment process of V-Ti-Ni shape memory alloy wire with a vanadium content of 2 at% in the preparation method of this invention is as follows:

[0636] like Figure 1 The process involves preparing commercially available sponge titanium, nickel, and a self-made vanadium-nickel alloy according to the V-Ti-Ni alloy composition (containing 2 at% V), and then obtaining V-Ti-Ni alloy wire according to the following steps: 1) Melting the raw materials in a vacuum medium-frequency induction furnace, with the vacuum degree controlled at 1×10 -2 1) After the raw material melts, it is protected by argon gas and cast into an ingot; 2) After the ingot is peeled and trimmed, it is placed in a box furnace for heating and held at 800℃ for 150 minutes, and then hot forged. The final forging temperature is controlled at 650℃ to obtain a square billet with a squareness of 50mm; 3) The 50mm square billet is placed in a box furnace for heating and held at 860℃ for 40 minutes, and then hot rolled to obtain a rod billet with a diameter of 10mm; 4) The rod billet is placed in a tube furnace for heating and held at 800℃ for 60 minutes, and then hot rolled to obtain a wire with a diameter of 3mm; 5) The 3mm wire is cold drawn to finally obtain a shape memory wire of 2V48.3Ti49.7Ni (Ti:Ni=49.3:50.7).

[0637] According to the process flow of Example 4, the final product is a V-Ti-Ni shape memory alloy wire, specifically a V2Ti wire that has undergone fine heat treatment and processing. 48.3 Ni49.7 Shape memory alloy wire is suitable for applications that require shape memory effect.

[0638] The final product of Example 4, V-Ti-Ni alloy wire, is composed of vanadium (V), titanium (Ti), and nickel (Ni), with a vanadium content of 2 at%, and a titanium to nickel ratio of Ti:Ni = 49.3:50.7. This means that the ratio of titanium to nickel in the V-Ti-Ni alloy is very close to 1:1, while the vanadium content is 2 atomic percent (at%). The V-Ti-Ni alloy wire is processed into a filament product through a series of heat treatment processes. V-Ti-Ni alloy wire belongs to shape memory alloy (SMA), which has the characteristic of recovering its original shape under external conditions (such as temperature changes). That is, the shape memory property of V-Ti-Ni alloy wire enables it to undergo reversible phase transformation under temperature changes or external forces. Especially in low-temperature environments, the transformation between its martensitic and austenitic phases makes it suitable for some special applications, such as deep-sea or deep-space exploration.

[0639] In terms of process details, the melting process in Example 4 uses a vacuum medium-frequency induction furnace for melting and is cast into ingots under argon protection. The heat treatment process in Example 4 includes peeling and trimming the ingots, heating, hot forging (controlling the forging temperature), hot rolling and cold drawing, etc., to gradually process them into the target shape. Finally, the V-Ti-Ni alloy is processed into wires with a diameter of 3mm through cold drawing, and the V-Ti-Ni alloy wires are ensured to have shape memory characteristics.

[0640] From the compositional analysis, the final V2Ti obtained 48.3 Ni 49.7 The alloy wire contains 2% vanadium (atomic percentage), while the ratio of titanium to nickel is Ti:Ni = 49.3:50.7. This reasonable combination of elements gives the alloy excellent shape memory properties, especially significant martensitic phase transformation characteristics at low temperatures.

[0641] Example 4 uses a V-Ti-Ni shape memory alloy with a 1 at% vanadium content, and employs a common vacuum induction furnace for melting and argon protection. The processing temperature and cold drawing process are also relatively standard. The process flow in Example 4 is consistent with conventional methods for producing vanadium-content alloy wires. Although Example 4 ensures the alloy composition and wire stability of the V-Ti-Ni shape memory alloy wire, the innovation in the process is relatively limited.

[0642] Example 5: Preparation and heat treatment process of V-Ti-Ni shape memory alloy wire with 5 at% vanadium content according to the preparation method of the present invention.

[0643] The preparation and heat treatment process of V-Ti-Ni shape memory alloy wire with a vanadium content of 5 at% in the preparation method of this invention is as follows:

[0644] like Figure 1 The process involves preparing commercially available sponge titanium, nickel, and a self-made vanadium-nickel alloy according to the V-Ti-Ni alloy composition (containing 5 at%), and then obtaining V-Ti-Ni alloy wire according to the following steps: 1) Melting the raw materials in a vacuum medium-frequency induction furnace, with the vacuum degree controlled at 1×10 -3 1) After the raw material melts, it is protected by argon gas and cast into an ingot; 2) After the ingot is peeled and trimmed, it is placed in a box furnace for heating and held at 880℃ for 120 minutes, and then hot forged. The final forging temperature is controlled at 650℃ to obtain a square billet with a squareness of 30mm; 3) The 30mm square billet is placed in a box furnace for heating and held at 870℃ for 30 minutes, and then hot rolled to obtain a rod billet with a diameter of 9mm; 4) The rod billet is placed in a tube furnace for heating and held at 900℃ for 30 minutes, and then hot rolled to obtain a wire with a diameter of 2mm; 5) The 2mm wire is cold drawn to finally obtain a 5V46.8Ti48.2Ni shape memory wire (Ti:Ni=49.3:50.7).

[0645] According to the process flow of Example 5, the goal of the process flow is to produce a V-Ti-Ni shape memory alloy wire through a series of steps such as melting, heat treatment, hot rolling and cold drawing.

[0646] The V-Ti-Ni shape memory alloy wire obtained in Example 5 has the composition of V5Ti. 46.8 Ni 48.2 The alloy contains 46.8% vanadium (V), 48.2% titanium (Ti), and 5% nickel (Ni). This is calculated based on the ratio of Ti:Ni = 49.3:50.7, which gives the specific content of titanium and nickel in the alloy. The vanadium content is 5 at%, and the ratio of titanium to nickel is close to 1:1, making it a V-Ti-Ni shape memory alloy.

[0647] In terms of shape memory effect, the V-Ti-Ni shape memory alloy wire obtained in Example 5 can be deformed under external force and recover its original shape under specific conditions (such as temperature change). The alloy exhibits a significant shape memory effect when the temperature changes.

[0648] In terms of production process, the V-Ti-Ni shape memory alloy wire obtained in Example 5 is obtained through multi-step processing. The melting process is carried out in a vacuum medium-frequency induction furnace, with the vacuum degree controlled at 1×10⁻⁶. -3To ensure high-quality V-Ti-Ni shape memory alloy wire, the V-Ti-Ni shape memory alloy undergoes a series of temperature holding processes, such as hot forging after holding at 880℃ for 120 minutes, hot rolling after holding at 870℃ for 30 minutes, and then heat treatment at 900℃. This optimizes the alloy's grain structure and phase transformation characteristics. The hot forging and hot rolling processes transform the V-Ti-Ni shape memory alloy ingot into smaller square billets and rods. Finally, a cold drawing process is used to draw the rods into Φ2mm wire, ensuring that the V-Ti-Ni shape memory alloy wire possesses good mechanical properties and shape memory characteristics.

[0649] In terms of physical properties, the shape memory characteristics of the V-Ti-Ni shape memory alloy wire obtained in Example 5 mainly stem from its unique phase transformation behavior. Within a specific temperature range, the alloy can recover its original shape and exhibit strong thermomechanical properties. Furthermore, through hot rolling and cold drawing, the strength and hardness of the V-Ti-Ni shape memory alloy are improved while maintaining good plasticity.

[0650] The product obtained in Example 5 is a V-Ti-Ni shape memory alloy wire containing 5% vanadium, which has excellent shape memory properties and can be widely used in high-end technology fields. The obtained V-Ti-Ni shape memory alloy wire is suitable for applications that require shape memory effects under temperature changes, such as for manufacturing stents or catheters in the medical device field, for automatically adjusting structural materials in the aerospace field, and for temperature control switches, sensors, or actuators in precision engineering.

[0651] Example 6: Preparation and heat treatment process of V-Ti-Ni shape memory alloy wire with 1 at% vanadium content according to the preparation method of the present invention.

[0652] The preparation and heat treatment process of V-Ti-Ni shape memory alloy wire with a vanadium content of 1 at% in the preparation method of this invention is as follows:

[0653] like Figure 1 The process involves preparing commercially available sponge titanium, nickel, and a self-made vanadium-nickel alloy according to the V-Ti-Ni alloy composition (containing 1 at%), and then obtaining V-Ti-Ni alloy wire according to the following steps: 1) Melting the raw materials in a vacuum medium-frequency induction furnace, with the vacuum degree controlled at 1×10 -21) After the raw material melts, it is protected by argon gas and cast into an ingot; 2) After the ingot is peeled and trimmed, it is placed in a box furnace for heating and held at 800℃ for 120 minutes, and then hot forged. The final forging temperature is controlled at 670℃ to obtain a square billet with a squareness of 40mm; 3) The 40mm square billet is placed in a box furnace for heating and held at 850℃ for 30 minutes, and then hot rolled to obtain a rod billet with a diameter of 8mm; 4) The rod billet is placed in a tube furnace for heating and held at 830℃ for 60 minutes, and then hot rolled to obtain a wire with a diameter of 2mm; 5) The 2mm wire is cold drawn to finally obtain a shape memory wire of 1V48.8Ti50.2Ni (Ti:Ni=49.3:50.7). Figure 2 This is the metallographic diagram of the alloy.

[0654] The wire obtained in Example 6 had the highest quality. In Example 6, the V-Ti-Ni shape memory alloy used a vanadium content of 1 at%, which is relatively low. In the preparation of V-Ti-Ni shape memory alloy wire with a vanadium content of 1 at%, more attention was paid to details in the hot forging and hot rolling processes of the ingot, especially in the precise control of different heating and heat treatment temperatures. This provides a new practical method for optimizing V-Ti-Ni shape memory alloy wire with a vanadium content of 1 at%.

[0655] Within the range of high-vanadium alloys (1 at%-5 at%), although the vanadium content of V-Ti-Ni shape memory alloy wire is relatively low (1 at%), ideal V-Ti-Ni shape memory alloy wire can be obtained by optimizing the heat treatment process. Example 6 ensures that even with a vanadium content of 1 at%, the V-Ti-Ni shape memory alloy still achieves the expected results in terms of alloy composition, grain refinement, and mechanical properties.

[0656] The objective of the process flow according to Example 6 is to produce V-Ti-Ni shape memory alloy wire with an alloy composition of V1Ti. 48.8 Ni 50.2 (Ti:Ni=49.3:50.7), the final product of Example 6, V-Ti-Ni shape memory alloy wire, contains 1 at% vanadium (V) and is obtained through a series of melting, heat treatment, hot rolling and cold drawing steps.

[0657] The alloy composition of the final product, V-Ti-Ni shape memory alloy wire, in Example 6 is: V1Ti 48.8 Ni 50.2(Ti:Ni=49.3:50.7), in which the vanadium (V) content is 1 at%, the titanium (Ti) content is 48.8%, and the nickel (Ni) content is 50.2%; the composition ratio of this alloy is very close to Ti:Ni=49.3:50.7, indicating that the V-Ti-Ni shape memory alloy wire is composed of almost equal proportions of titanium and nickel, and belongs to the product with relatively low vanadium content among "high vanadium alloys".

[0658] The final product of Example 6, V-Ti-Ni shape memory alloy wire, has shape memory properties and can recover to a preset shape under certain temperature changes. This property allows the alloy to recover to its original state through heating or cooling after being deformed by external force. It is commonly used in aerospace, medical equipment and smart materials.

[0659] From a production process perspective, the final product of Example 6, the V-Ti-Ni shape memory alloy wire, involves melting sponge titanium, nickel, and a self-made vanadium-nickel alloy according to a predetermined composition during the smelting stage. The vacuum degree is controlled at 1×10⁻² to ensure the purity of the V-Ti-Ni shape memory alloy. In the heat treatment stage, hot forging and hot rolling are performed in a box furnace, gradually processing the alloy from a large-sized ingot into square billets and rod billets, ultimately producing a Φ2mm wire. Temperature and time control during the heating process helps optimize the grain size, ensuring the mechanical properties of the alloy wire. The heat treatment temperatures are as follows at different stages: in hot forging, the alloy is held at 800℃ for 120 minutes, with a final forging temperature of 670℃; in hot rolling, it is held at 850℃ for 30 minutes, further cooled, and then hot rolled; finally, it is held at 830℃ for 60 minutes, resulting in the final alloy wire. These heat treatment steps help form a grain structure suitable for the shape memory effect. Finally, the alloy wire is further processed by cold drawing to achieve the final shape memory wire, which has good mechanical properties and high tensile strength.

[0660] From both physical and microstructural perspectives, the final product of Example 6, the V-Ti-Ni shape memory alloy wire, exhibits an austenitic grain structure. The grain size was refined through temperature control and cold drawing. Due to the low vanadium content (only 1%), the strengthening of this alloy primarily derives from the alloying effect of titanium and nickel.

[0661] The product obtained in Example 6 is a V-Ti-Ni shape memory alloy wire containing 1 at% vanadium, which exhibits shape memory effect and undergoes multiple precise heat treatment and cold drawing processes. These process steps ensure that the alloy wire has ideal microstructure and mechanical properties, making it suitable for high-end technology fields, especially applications requiring shape memory characteristics, such as the manufacture of stents, catheters, and therapeutic tools in the medical device field; smart materials that automatically adjust shape or respond to changes in external temperature in aerospace and engineering applications; and sensors and actuators in temperature control switches, deformable materials, and actuators.

[0662] Example 7: Preparation and heat treatment process of V-Ti-Ni shape memory alloy wire with a vanadium content of 3 at% according to the preparation method of the present invention.

[0663] The preparation and heat treatment process of V-Ti-Ni shape memory alloy wire with a vanadium content of 3 at% in the preparation method of this invention is as follows:

[0664] like Figure 1 The process involves preparing commercially available sponge titanium, nickel, and a self-made vanadium-nickel alloy according to the V-Ti-Ni alloy composition (containing 3 at%), and then obtaining V-Ti-Ni alloy wire according to the following steps: 1) Melting the raw materials in a vacuum medium-frequency induction furnace, with the vacuum degree controlled at 1×10 -3 1) After the raw material melts, it is protected by argon gas and cast into an ingot; 2) After the ingot is peeled and trimmed, it is placed in a box furnace for heating and held at 870℃ for 90 minutes, and then hot forged. The final forging temperature is controlled at 680℃ to obtain a square billet with a squareness of 30mm; 3) The 30mm square billet is placed in a box furnace for heating and held at 890℃ for 40 minutes, and then hot rolled to obtain a rod billet with a diameter of 10mm; 4) The rod billet is placed in a tube furnace for heating and held at 860℃ for 60 minutes, and then hot rolled to obtain a wire with a diameter of 3mm; 5) The 3mm wire is cold drawn to finally obtain a shape memory wire of 3V47.8Ti49.2Ni (Ti:Ni=49.3:50.7).

[0665] According to the description in Example 7, the final product obtained is a V-Ti-Ni shape memory alloy wire, which contains 3 at% vanadium (V) and is V3Ti. 47.8 Ni 49.2 Shape memory filament.

[0666] The final product obtained in Example 7 is a V-Ti-Ni shape memory alloy wire, with an alloy composition of V3Ti. 47.8 Ni 49.2 ,

[0667] The alloy contains 3 at% vanadium (V), 47.8% titanium (Ti), and 49.2% nickel (Ni). The ratio of titanium to nickel in this alloy is close to 1:1, and the vanadium content is relatively low, although it still plays a role in enhancing the alloy's properties.

[0668] The final product obtained in Example 7 is a V-Ti-Ni shape memory alloy wire, which exhibits significant shape memory properties, meaning it can deform under external force and recover its original shape upon temperature changes (such as heating). Due to the addition of vanadium, the alloy's shape memory temperature range is improved, making it suitable for a wider range of high-temperature environments.

[0669] The final product obtained in Example 7 is a V-Ti-Ni shape memory alloy wire. In terms of the production process, the melting stage involves melting sponge titanium, nickel, and a self-made vanadium-nickel alloy according to the V-Ti-Ni composition, with the vacuum degree controlled at 1×10⁻⁶. -3 To ensure the purity and uniformity of the alloy, the heat treatment process involves hot forging and hot rolling of the ingot, holding it sequentially at 870℃ and 890℃ to adjust the alloy's grain structure, giving it better machinability and mechanical properties. In the hot forging stage, the ingot is held at 870℃ for 90 minutes, with the final forging temperature controlled at 680℃, to forge a square billet. In the hot rolling stage, the ingot is first held at 890℃ for 40 minutes and then hot-rolled into a Φ10mm rod, followed by a holding at 860℃ for 60 minutes and then hot-rolled into a Φ3mm wire. The cold drawing stage involves cold drawing the final alloy wire into a Φ3mm wire, ensuring it possesses the required mechanical properties and shape memory characteristics.

[0670] From a physical and microstructural perspective, the final product obtained in Example 7 is a V-Ti-Ni shape memory alloy wire, the microstructure of which is optimized through these heat treatment processes. Due to the high vanadium content (3%), the grains of the V-Ti-Ni shape memory alloy wire are refined, enhancing its strength and toughness. Its main microstructure is austenitic grains, but due to the addition of vanadium, the V-Ti-Ni shape memory alloy wire exhibits some tiny second-phase particles, which contribute to enhancing the alloy's mechanical properties and shape memory characteristics.

[0671] The final product obtained in Example 7 is a V-Ti-Ni shape memory alloy wire, which exhibits excellent shape memory effect and is suitable for temperature control and adaptive applications, especially in the medical and aerospace fields, where it has broad application prospects. It is particularly suitable for fields requiring smart and temperature-responsive materials, such as the manufacture of stents, catheters, and treatment tools in medical devices; adaptive structures and temperature control materials in aerospace; temperature control switches, transmission devices, or other intelligent mechanical systems in sensors and actuators.

[0672] The wire obtained in Example 7 has higher quality. In Example 6, the V-Ti-Ni shape memory alloy has a vanadium content of 3 at%, and the heat treatment temperature is controlled more strictly. Different hot rolling and heat treatment processes were performed for different alloy compositions. By adjusting the hot rolling and heat treatment temperatures, Example 7 can improve the overall performance of the V-Ti-Ni shape memory alloy wire.

[0673] Within the range of high-vanadium alloys (1 at%-5 at%), a vanadium content of 3 at% is moderate, thus achieving a better balance between performance and processing compared to low-vanadium alloys. Example 7 shows a V-Ti-Ni shape memory alloy wire with a vanadium content of 3 at%, but significant process improvements and optimizations are still needed.

[0674] Measurement results of the as-cast microstructure of the high-vanadium V-content V-Ti-Ni shape memory alloy described in this invention.

[0675] The present invention describes the determination of the as-cast microstructure of a high-vanadium (V) content V-Ti-Ni shape memory alloy. It correlates each step of the S2 composition design and preliminary preparation stage (especially S2.1 to S2.5) with the microscopic technical effects reflected in actual scanning electron microscopy (SEM) images, demonstrating the logical chain of "process → microstructure → properties". The purpose of this table is to support the scientific validity and effectiveness of the technical approach with microstructural evidence. Figure 2 The image shown is a scanning electron microscope (SEM) image (magnification: 1000×) of V-Ti-Ni shape memory alloy in its as-cast state. This is an early microstructure result of the high vanadium content V-Ti-Ni shape memory alloy preparation method shown in this invention, reflecting the microstructure characteristics of the V-Ti-Ni shape memory alloy after completing the S2.5 melting step and before entering hot forging or heat treatment.

[0676] Figure 2 It is evident that the microstructure of the V-Ti-Ni shape memory alloy consists of regular equiaxed grains with a grain size of 10–50 μm, clear grain boundaries, and no obvious segregation or inclusions. This indicates that the composition design and melting process control of the present invention are appropriate, providing a good microstructure basis for subsequent hot working and shape memory performance stability.

[0677] From the perspective of grain morphology characteristics Figure 2The microstructure clearly shows polygonal grain outlines, with most grains being equiaxed. This indicates that the V-Ti-Ni shape memory alloy underwent a moderate cooling rate during solidification, preventing the growth of highly directional columnar crystals. Furthermore, the grain boundaries are distinct yet smooth, without obvious coarse segregation bands or dendritic dissolution marks. The as-cast microstructure of the V-Ti-Ni shape memory alloy exhibits irregular grain morphology, suggesting that the grains did not grow or crystallize completely uniformly during cooling. During casting, especially at faster cooling rates, larger grains or irregularly shaped grains may result. As this is an as-cast microstructure of a V-Ti-Ni shape memory alloy, significant grain boundaries exist between the grains, representing the interactions and property differences between different grains.

[0678] Figure 2 The alloy crystals exhibit a polygonal equiaxed grain structure with natural grain boundaries and smooth edges, showing no severe dendrite reconstruction or anisotropic crystallization characteristics. This indicates that: firstly, the V-Ti-Ni shape memory alloy described in this invention exhibits a moderate and stable overall cooling rate during solidification, avoiding the formation of a large number of columnar crystals; secondly, the V-Ti-Ni shape memory alloy described in this invention does not show obvious segregation interfaces or secondary dendrite dissolution phenomena, demonstrating a balanced microstructure and high interface integrity; thirdly, the melt of the V-Ti-Ni shape memory alloy described in this invention is fully homogenized during heat preservation and stirring, with controlled solidification behavior, weak crystallization directionality, and anisotropic microstructure orientation, which is beneficial for subsequent hot working. From the perspective of grain morphology... Figure 2 The grain structure exhibited shows that the grains have different sizes and shapes, with some grains exhibiting polygonal or irregular shapes. This is usually a natural result of the casting process. In terms of phase distribution, in V-Ti-Ni shape memory alloys, vanadium (V), as an alloying element, forms some second-phase particles. These particles are usually embedded between or inside the matrix grains, affecting the properties of V-Ti-Ni shape memory alloys; the distribution, morphology, and size of these particles are smaller than those of the matrix grains.

[0679] In terms of grain size range Figure 2The scale bar is 50 μm, suggesting an average grain diameter between 10 and 50 μm, with uniform grain size distribution and no abnormalities of excessively large or small grains. This indicates that the melting process in the preparation method described in this invention has good thermal control, sufficient material preparation, and uniform composition; vanadium (V) did not form obvious grain boundary depletion zones. Based on the scale bar (50 μm) in the figure, it can be inferred that the average grain size range of the V-Ti-Ni shape memory alloy described in this invention is approximately 10–50 μm, with minimal grain size variation. Specifically: First, the V-Ti-Ni shape memory alloy described in this invention has a relatively uniform grain size distribution, with no large-sized abnormal grains or localized coarsening observed, and the melting thermal field is well controlled, with strong cooling uniformity and sufficient component diffusion. Second, from a compositional design perspective, the addition of V did not cause localized cooling rate runaway or non-uniform crystallization behavior.

[0680] From the perspective of intracrystalline and grain boundary structure Figure 2 The intragranular structure is relatively pure, with no dense precipitates observed, and a small number of bright spots or white speckled particles are present. After analysis, these are identified as V-rich phases, oxides, or other inclusions. These particles are sparsely distributed and do not aggregate along grain boundaries or form a network structure, indicating that the influence of these particles on the alloy matrix is ​​controllable. Therefore, the overall quality of the high-vanadium V-content V-Ti-Ni shape memory alloy prepared by this invention is guaranteed. The intragranular region of the V-Ti-Ni shape memory alloy described in this invention exhibits overall purity and uniformity, with no obvious precipitate network or agglomeration. A small number of bright spots or white speckled particles are visible locally. Preliminary EDS analysis suggests that the V-Ni pre-alloying mixing strategy employed in the process system for the high-vanadium V-content V-Ti-Ni shape memory alloy described in this invention effectively suppresses V oxidation loss and segregation tendency. The type and size of the resulting inclusions are controllable, having minimal impact on the alloy matrix structure of the V-Ti-Ni shape memory alloy. The overall V-Ti-Ni shape memory alloy material has high purity, suitable for subsequent hot forging and stability requirements of shape memory behavior.

[0681] In terms of crystal type, due to the presence of elements such as titanium, nickel, and vanadium in V-Ti-Ni shape memory alloys, the matrix of V-Ti-Ni shape memory alloys exhibits a body-centered cubic (BCC) or face-centered cubic (FCC) crystal structure. Under different heat treatment conditions, V-Ti-Ni alloys undergo martensitic phase transformation, and these crystals exhibit different phase types. From a martensitic crystal structure perspective, V-Ti-Ni shape memory alloys exhibit a martensitic phase at specific temperatures, which manifests as a change in the crystal lattice structure in microscopic images, resulting in different lattice morphologies or phase boundaries. From a grain boundary perspective, due to the relatively rapid cooling rate of cast V-Ti-Ni shape memory alloys, the boundaries between grains appear relatively rough.

[0682] like Figure 2As shown, the significance of the as-cast microstructure diagram of V-Ti-Ni shape memory alloy in the technical solution described in this invention is as follows:

[0683] In the technical approach of the present invention for a high vanadium (V) content V-Ti-Ni shape memory alloy, such as... Figure 2 The SEM images shown indicate that: First, the prepared V-Ti-Ni shape memory alloy exhibits good microstructure consistency and structural purity in the as-cast state; second, the initial grain morphology of the prepared V-Ti-Ni shape memory alloy is good, meeting the requirements of subsequent hot forging, hot rolling, and cold drawing processes; third, the microstructure stability of the prepared V-Ti-Ni shape memory alloy demonstrates that the "batching-mixing-melting" process design of this invention is reasonable and the process is stable; fourth, the prepared V-Ti-Ni shape memory alloy is an important structural prerequisite for developing low-temperature functional shape memory alloy materials.

[0684] This indicates that the prepared V-Ti-Ni shape memory alloy exhibits a good initial grain morphology, meeting the requirements of subsequent hot forging, hot rolling and cold drawing processes; the prepared V-Ti-Ni shape memory alloy has a stable microstructure, indicating that the preparation method of the present invention has a reasonable process design, especially the "batch-mixing-melting process" step design is reasonable and the process is stable, meeting the important structural prerequisite for developing low-temperature functional shape memory alloy materials.

[0685] Furthermore, SEM images of the V-Ti-Ni shape memory alloy at 1000× magnification, combined with the preparation process (S2.1–S2.5) and subsequent processes (S3 hot forging, S4 hot rolling, S5 cold drawing), provide a comparative analysis of the microstructure evolution (cast state → hot-worked state) of the high-vanadium V-content V-Ti-Ni shape memory alloy described in this invention. The specific comparative analysis is as follows:

[0686] from Figure 2 As can be seen, the microstructure of the V-Ti-Ni shape memory alloy mainly consists of equiaxed polygonal grains with a grain size between 10 and 50 μm. The grains are relatively uniformly distributed, with clear grain boundaries and no obvious coarsening or directional segregation, indicating stable crystallization during solidification. Furthermore, no obvious agglomeration or inclusions of precipitates were observed at grain boundaries or within the grains, suggesting uniform powder mixing in step S2.4, effective atmosphere control during melting in step S2.5, and uniform doping of vanadium (V) without significant volatilization or segregation.

[0687] In summary, Figure 2The as-cast microstructure clearly shows that the as-cast structure of the V-Ti-Ni shape memory alloy described in this invention provides a good structural basis for subsequent hot forging, possesses excellent hot working adaptability and compositional uniformity, and verifies the practicality and structural controllability of the preparation process of this invention. The V-Ti-Ni shape memory alloy proposed in this invention has a reasonable compositional design and appropriate control of the mixing and melting processes, ultimately forming an as-cast structure with uniform grains, clear interfaces, and controllable inclusions. This lays a good foundation for the microstructure reconstruction and repeatability of the memory effect during subsequent hot working.

[0688] Determination 2: Definition of "high vanadium" in the high vanadium V-Ti-Ni shape memory alloy described in this invention.

[0689] Regarding the high vanadium (V) content V-Ti-Ni shape memory alloy and its preparation method described in this invention, the definition of vanadium (V) content in V-Ti-Ni shape memory alloy as 1%-5% (atomic percentage) is actually a high vanadium alloy, which is related to the characteristics and application requirements of the V-Ti-Ni shape memory alloy material obtained by preparation.

[0690] Vanadium is a relative content comparison. In the high vanadium (V) content V-Ti-Ni shape memory alloy described in this invention, titanium (Ti) and nickel (Ni) are the main alloying elements, with a ratio of Ti:Ni = 49.3:50.7, close to a 1:1 ratio. In comparison, the vanadium content is 1%-5%, which is relatively high. Furthermore, comparing the vanadium content with the ratio of Ti and Ni, it can be seen that 1%-5% vanadium content constitutes a significant proportion in such an alloy system. Even in other alloys, alloys with 5% vanadium content are often considered high-vanadium alloys because vanadium itself is not a major element in the alloy, and 1%-5% is already a significant proportion.

[0691] From the perspective of vanadium's role and influence, vanadium is an alloy strengthening element that can significantly improve the mechanical properties of V-Ti-Ni shape memory alloys, such as strength, hardness, and elasticity, and also helps improve their thermal stability and corrosion resistance. In the V-Ti-Ni shape memory alloys described in this invention, when the vanadium content reaches 1%-5%, it significantly alters the phase transformation temperature, shape memory effect, and other important physicochemical properties of the V-Ti-Ni shape memory alloy. The addition of vanadium affects the martensitic phase transformation temperature of Ti-Ni alloys. Excessively high vanadium content makes V-Ti-Ni shape memory alloys more suitable for low-temperature applications, such as deep-sea or deep-space exploration. Therefore, a vanadium content of 5% is relatively high compared to ordinary Ti-Ni alloys (which typically contain very little vanadium).

[0692] From the perspective of alloy performance requirements, the addition of vanadium in V-Ti-Ni shape memory alloys is mainly to optimize the alloy's low-temperature characteristics. Increasing the vanadium content leads to better performance of V-Ti-Ni shape memory alloys at low temperatures. Therefore, for these special low-temperature applications, such as deep-sea and deep-space exploration, a vanadium content of 1%-5% is a suitable high content, as high-vanadium V-Ti-Ni shape memory alloys can meet the specific requirements of these applications.

[0693] In practical applications of alloys, vanadium is added as an alloying element in traditional Ti-Ni alloys, but its content is usually low. With increasing vanadium content, the effects of the V-Ti-Ni shape memory alloy described in this invention become more significant in various fields, especially in environments requiring higher performance. A vanadium content of 5% can significantly affect the martensitic transformation temperature and increase the alloy's strength properties; therefore, this range of vanadium content constitutes a high-vanadium alloy, meaning the V-Ti-Ni shape memory alloy described in this invention belongs to the high-vanadium alloy category.

[0694] In summary, the 1%-5% vanadium content obtained by this invention is relatively high in V-Ti-Ni alloys, especially when the ratio of titanium to nickel is fixed. Vanadium content significantly affects the performance of the V-Ti-Ni shape memory alloy described in this invention, particularly in low-temperature performance and shape memory characteristics; therefore, this range of vanadium content is considered a high-vanadium alloy.

[0695] Comparative analysis of the preparation methods of the high vanadium (V) content V-Ti-Ni shape memory alloy described in Examples 4-7 of this invention.

[0696] This invention relates to a high vanadium (V) content V-Ti-Ni shape memory alloy and its preparation method. A systematic comparative analysis of the differences in the preparation methods of Examples 4–7 is conducted, focusing on the setting of vanadium (V) content, melting parameters, hot forging / hot rolling schemes, and size control strategies. The analysis also explains the resulting differences in microstructure, changes in processing performance, and the impact on final functionality.

[0697] The main differences in the preparation methods of the high vanadium (V) content V-Ti-Ni shape memory alloy described in Examples 4-7 of this invention are as follows:

[0698] The results of the differences in the preparation methods of Examples 4-7 of the present invention regarding the high vanadium (V) content V-Ti-Ni shape memory alloy are compared as follows:

[0699] Firstly, the difference in vanadium (V) content affects the structure and properties.

[0700] This indicates that the preparation method of the high vanadium V content V-Ti-Ni shape memory alloy of the present invention increases lattice distortion as the vanadium V content increases, which promotes grain refinement, but also introduces vanadium-rich V phase and reduces deformation capacity and plasticity.

[0701] Secondly, differences in vacuum level affect purity and inclusion control. Specifically, Examples 4 and 7 used a higher vacuum level (1×10⁻⁶). -3 Pa) is beneficial for reducing oxygen content and smelting inclusions, especially significantly affecting the stability of vanadium (V); Examples 4 and 6 are performed under ordinary vacuum (1×10⁻⁶ Pa). -2 While the purity control is slightly inferior (Pa), it is sufficient to meet the requirements for smelting with low V content.

[0702] This indicates that the preparation method of the high vanadium V content V-Ti-Ni shape memory alloy of the present invention is that vanadium V is easily oxidized, increasing the vacuum degree can improve the doping utilization rate, reduce the aggregation of vanadium V oxidation components, and enhance the uniformity of the structure.

[0703] Third, hot forging / hot rolling parameters affect the grain reconstruction mechanism.

[0704] This indicates that the preparation method of the high vanadium V content V-Ti-Ni shape memory alloy described in this invention, with its higher hot working temperature and holding time, makes it easier for the V-Ti-Ni shape memory alloy material to form subgrain boundaries and fine grains, thereby enhancing the stability of the microstructure after processing. However, coarsening or oxidation must be prevented.

[0705] Fourth, differences in dimensional paths affect forming behavior. In Examples 5 and 6, Φ2mm terminal diameter wires were used, and combined with the cold drawing process, the microstructure was further refined, and the structural density and springback were improved. Examples 4 and 7 retained Φ3mm wires, resulting in slightly lower subsequent deformation stress, which is suitable for forming flexible memory devices.

[0706] This demonstrates that, in the preparation method of the high vanadium V-content V-Ti-Ni shape memory alloy described in this invention, radial thinning of the wire and cold drawing stress are important means to control the memory strain and recovery rate, and different final diameters are suitable for different loading scenarios.

[0707] Fifth, a summary of the overall effects of the V-Ti-Ni shape memory alloy material described in this invention.

[0708] Measurements show that the differences in V content, melting vacuum degree, and hot working path among the four embodiments described in this invention result in significant microstructure evolution and performance gradients. Experimental results indicate that 1%-3% V doping can achieve grain refinement and memory window control while ensuring good processing performance, while the 5% high-doped alloy, although slightly less processable, possesses structural and responsive advantages in cryogenic applications. Systematic optimization of different process parameters provides a reliable process basis for the customized design of V-Ti-Ni high-vanadium memory alloys.

[0709] Comparative analysis of the alloy products of Examples 4-7 of the high vanadium (V) content V-Ti-Ni shape memory alloy described in this invention.

[0710] Regarding the high vanadium (V) content V-Ti-Ni shape memory alloy and its preparation method described in this invention, Examples 4-7 all adopted the same basic preparation process path ( Figure 1 The process is as follows: batching → smelting → hot forging → hot rolling → cold drawing. However, there are differences in vanadium (V) content, heat treatment parameters, and final wire dimensions. This is because the vanadium (V) doping ratio and heat treatment process have a significant impact on crystal structure, morphological evolution, microstructure stability, and shape memory behavior.

[0711] Firstly, the crystal structure characteristics of the high vanadium (V) content V-Ti-Ni shape memory alloy described in this invention include the main phase structure, phase transformation characteristics, and the influence of vanadium (V); specifically as follows:

[0712] In Example 4 (2%V), the V-Ti-Ni shape memory alloy has an average grain size of 10–20 μm, a uniform structure, a small number of subgrain boundaries, and a moderate microstructure, making it suitable for general applications. In Example 5 (5%V), the V-Ti-Ni shape memory alloy has fine grains (5–12 μm), locally visible precipitated phase particles, and active grain boundaries, showing strengthening effect and potential for phase transformation control. In Example 6 (1%V), the V-Ti-Ni shape memory alloy has the largest grains (10–25 μm), a complete and clear microstructure, no obvious enriched phases, and is closest to traditional TiNi alloys. In Example 7 (3%V), the V-Ti-Ni shape memory alloy has significantly refined grains, locally exhibiting slip bands and twin structures, showing good recrystallization activity.

[0713] This indicates that in the crystal of the V-Ti-Ni shape memory alloy with high vanadium V content described in this invention, the higher the vanadium V content, the greater the disturbance to the B2 phase lattice and the stronger the ability to suppress martensitic phase transformation; the sample with the highest vanadium V content (Example 5) is more suitable for low temperature or cryogenic deformation environment; while the sample with the lowest vanadium V content (Example 6) retains the traditional TiNi memory window and is suitable for conventional driving.

[0714] Secondly, the microstructure and grain morphology of the V-Ti-Ni shape memory alloy with high vanadium (V) content described in this invention are compared as follows:

[0715] This indicates that, among the microstructure and grain morphology of the high vanadium V-content V-Ti-Ni shape memory alloy described in this invention, Example 5 (5%V) has the finest microstructure, accompanied by the precipitation of vanadium-rich V phase, making it more compact overall; Example 6 (1%V) has grains that are closest to the equiaxed crystal morphology of traditional TiNi, which is suitable for low stress state after hot working; Example 7 has higher hot forging and hot rolling temperature settings, which is conducive to dynamic recrystallization and twin formation.

[0716] Thirdly, the final wire morphology and machinability of the high vanadium (V) content V-Ti-Ni shape memory alloy described in this invention are compared as follows:

[0717] This indicates that, in comparison of the final wire morphology and machinability of the high vanadium V content V-Ti-Ni shape memory alloy described in this invention, the highest vanadium V alloy (Example 5) has higher wire hardness and is suitable for structural load-bearing applications; the lowest vanadium V alloy (Example 6) has better formability and is suitable for fine wire preparation and micro-drawing environments; Examples 4 and 7 maintain a good balance between machinability and shape memory performance.

[0718] To further verify the adaptability and effectiveness of the high-vanadium-content V-Ti-Ni shape memory alloy preparation method described in this invention, Examples 4 to 7 were selected for systematic comparison, covering the differences in alloy composition design, hot working process, and final microstructure and properties under different vanadium V doping ratios (1%, 2%, 3%, 5%). The specific performance predictions and applicability analyses are as follows:

[0719] This demonstrates that the V-Ti-Ni shape memory alloy materials with different doping ratios described in this invention exhibit significant differences in microstructure, processability, and functional response: 1%-3% vanadium V doping can effectively refine grains while balancing processability and performance stability, making it suitable for most industrial and medical applications; although 5% V doping reduces processing plasticity, it has unique advantages in low-temperature structural material scenarios, making it suitable for use in low-temperature environments, and is a functional shape memory alloy material for deep-sea and deep-space exploration.

Claims

1. A method for preparing a V-Ti-Ni shape memory alloy with high vanadium (V) content, characterized in that, Includes the following steps: S1. Density Functional Theory (DFT) Calculation Optimization of Vanadium (V) Content: Using conventional DFT calculation convergence criteria, the optimal vanadium content range is determined through crystal structure modeling, parameter setting, energy calculation, and performance prediction. S1.1 Establishing a crystal structure model: Using the B2 phase of TiNi alloy as the parent crystal, a supercell model is constructed, and the atoms at Ti or Ni sites are systematically replaced with vanadium V atoms to form models with different doping ratios. S1.2 Set calculation parameters: Use GGA-PBE functional to perform structural relaxation and energy calculations, and evaluate the total energy, elastic constant and phase transition energy barrier of each doped model; S1.3 Doping Scheme Design and Modeling: Vanadium V is introduced by preferentially replacing titanium Ti sites in TiNi B2 matrix. Ordered model, random model and SQS doping model are constructed and DFT calculation is performed independently. The effects of different substitution methods on lattice stability, martensitic phase transition tendency and electronic structure are compared. Statistical error is evaluated and the best doping strategy is screened to reduce lattice distortion and stress-induced phase transition temperature. S1.4 Performance Trend Analysis: Analyze the relationship between doping ratio and performance indicators, and summarize the changes in mechanical properties and martensitic phase transformation temperature under different V contents; S1.5 Conclusion Output: Determine the optimal atomic percentage range of vanadium doping, replace Ti atoms with the optimal low-temperature phase transformation control range, and then provide feedback to guide the actual alloy composition design and smelting ratio; S2. Alloy composition design and batching: First, select and pre-treat the raw materials, then design the alloy composition; S3. Raw material pretreatment: The determined titanium (Ti), nickel (Ni), and vanadium (V) raw materials are pretreated before smelting; S4. Vacuum induction furnace melting and ingot casting: The alloy batches are melted in a vacuum induction furnace and protected with argon gas, and then cast into ingots; S5. Billet trimming and heating homogenization: After peeling and trimming the alloy billet, it is heated and homogenized. S6. Hot forging: Alloy ingots are hot forged to form alloy square billets; S7. First hot rolling: The alloy square billet undergoes multiple hot rolling passes to form a rod billet; S8. Second hot rolling: The alloy rod billet undergoes multiple hot rolling passes to form wire; S9. Cold drawing: Cold drawing alloy wire to obtain the final product.

2. The method for preparing a V-Ti-Ni shape memory alloy with high vanadium (V) content according to claim 1, characterized in that, Method S2, alloy composition design and batching, includes a method for designing the composition of a V-Ti-Ni shape memory alloy, specifically comprising the following steps: S2.1 Determine the source of elements and raw materials: Vanadium V, titanium Ti, and nickel Ni are selected as the alloy system, and vanadium V is introduced in the form of V-Ni pre-alloy; S2.2 Atomic Ratio Setting: Controlling the vanadium content control range, determining the fixed ratio of titanium and nickel, and constructing a typical vanadium V doping ratio matrix; S2.3 Atomic Ratio-Mass Ratio Conversion: Obtain the molar mass of V, Ti, and Ni, convert the atomic percentage to mass percentage for any total amount, and perform mass breakdown conversion for V-Ni pre-alloys; S2.4 Mixing process design: Under inert atmosphere or vacuum environment, a V-Ni pre-alloying + Ti mixing strategy is adopted to optimize the mixing method and uniformity detection; S2.5 Subsequent Smelting Parameter Recommendations.

3. The method for preparing a V-Ti-Ni shape memory alloy with high vanadium (V) content according to claim 1, characterized in that, Method S3. Raw material pretreatment includes a raw material pretreatment method for preparing high vanadium content V-Ti-Ni shape memory alloys, with the following specific steps: S3.1 Material Selection and Acceptance: Sponge titanium, high-purity nickel, and self-made vanadium-nickel alloy are selected as alloy raw materials, and a batch traceability system is established; S3.2 Surface pretreatment: The raw material is surface-trimmed and dried; S3.3 Proportioning and Weighing: Based on the designed alloy atomic percentage, adjust the amount of pure nickel to be fed after component separation of the V-Ni pre-alloy; S3.4 Crushing and Particle Size Control: Repairing alloy raw materials and controlling particle size; S3.5 encapsulates and stores raw materials.

4. The method for preparing a V-Ti-Ni shape memory alloy with high vanadium (V) content according to claim 1, characterized in that, Method S4, vacuum induction furnace melting and ingot casting, includes a method for vacuum induction furnace melting and ingot casting of V-Ti-Ni shape memory alloy, the specific steps of which are as follows: S4.1 Raw material charging into the furnace: The Ni, V-Ni pre-alloy and Ti raw materials weighed in proportion are charged into the furnace in sequence; S4.2 Vacuum evacuation and preheating: The furnace cavity is evacuated and the alloy after loading is preheated at low temperature; S4.3 Induction heating and melting homogenization: Start medium-frequency induction heating, heat up to melt the alloy raw material, and then stir and hold at the temperature; S4.4 Atmosphere switching and argon protection: After the melt stabilizes, argon is introduced to create a positive pressure protective atmosphere; S4.5 Casting into ingots: Under argon protection, the melt is poured into a mold for natural cooling; S4.6 Ingot removal and preliminary inspection.

5. The method for preparing a V-Ti-Ni shape memory alloy with high vanadium (V) content according to claim 1, characterized in that, Method S5. Ingot trimming and heating homogenization includes an ingot trimming and heating homogenization method for preparing high vanadium content V-Ti-Ni shape memory alloys, the specific steps of which are as follows: S5.1 Peeling and trimming: Peeling and trimming the billet; S5.2 Ingot loading and furnace heating: The trimmed ingots are heated in stages; S5.3 Insulation treatment: First, the alloy ingot is insulated, then cooled and the protective atmosphere is maintained; S5.4 The billet is removed.

6. The method for preparing a V-Ti-Ni shape memory alloy with high vanadium (V) content according to claim 1, characterized in that, Method S6, hot forging, includes a hot forging method for V-Ti-Ni shape memory alloys, with the following specific steps: S6.1 Billet trimming: The billet is trimmed by peeling off the skin, and heat preservation or insulation measures are taken at the same time. S6.2 Heating of billet before hot forging: The trimmed billet is heated in stages and then kept warm in an inert atmosphere; S6.3 Hot forging deformation: The ingot after heat preservation is hot forged to obtain a square billet with a specification of 30mm-60mm; S6.4 Billet Cooling and Transfer.

7. The method for preparing a V-Ti-Ni shape memory alloy with high vanadium (V) content according to claim 1, characterized in that, Method S7. First hot rolling includes a first hot rolling method for a high vanadium content V-Ti-Ni shape memory alloy, the specific steps of which are as follows: S7.1 Billet Heating: The billet is heated, and real-time monitoring and argon gas protection are performed; S7.2 Rolled bar blank: The square billet is hot rolled into a bar blank with a diameter of Φ6 mm to Φ12 mm through a multi-pass hot rolling process; S7.3 Cooling and Inspection after Hot Rolling: Cool the billet and inspect its quality.

8. The method for preparing a V-Ti-Ni shape memory alloy with high vanadium (V) content according to claim 1, characterized in that, Method S8. Second hot rolling includes a second hot rolling method for a high vanadium content V-Ti-Ni shape memory alloy, the specific steps of which are as follows: S8.1 Bar billet heating: The bar billet is heated in the furnace while maintaining an inert gas protective atmosphere; S8.2 Rolling: The bar billet is hot rolled in multiple passes to form wire with a diameter of Φ2mm-Φ3mm; S8.3 Wire cooling and quality inspection.

9. The method for preparing a V-Ti-Ni shape memory alloy with high vanadium (V) content according to claim 1, characterized in that, Method S9. Cold drawing includes a cold drawing method for a high vanadium content V-Ti-Ni shape memory alloy, the specific steps of which are as follows: S9.1 Wire preparation and surface cleaning: Surface cleaning of Φ2mm-Φ3mm wire obtained from the second hot rolling; S9.2 Installation and parameter setting of drawing equipment: Assemble the cold drawing equipment and mold, and set the drawing speed, drawing tension and lubrication conditions; S9.3 Cold drawing operation: Use multi-segment or continuous drawing method to gradually reduce the diameter of the wire; S9.4 Finished product inspection and packaging.

10. The method for preparing a V-Ti-Ni shape memory alloy with high vanadium (V) content according to claim 1, characterized in that, The method S1, density functional theory (DFT) calculation for optimizing vanadium V content, includes: In S1.1 establishing the crystal structure model, the supercell model is a 3×3×3 B2TiNi supercell with 54 atoms and a doping ratio of 1%-10%; In the S1.5 conclusion, the optimal range for low-temperature phase transition control is between 1.85% and 5.56%, which is between 1 V / 54 atom and 3 V / 54 atom.

11. The method for preparing a V-Ti-Ni shape memory alloy with high vanadium (V) content according to claim 2, characterized in that, The method S2. Alloy composition design and batching includes: In S2.1, the V:Ni molar ratio of the V-Ni pre-alloy is 1:2, which determines the source of elements and raw materials. In S2.2 atomic ratio settings, the atomic percentage of vanadium content is 1%–5%, the fixed ratio of titanium and nickel is Ti:Ni=49.3:50.7, and the vanadium content in the proportioning matrix is ​​set to 1%, 3%, and 5%. In the S2.3 atomic ratio-mass ratio conversion, the mass breakdown of the V-Ni pre-alloy can be achieved using the following formula: in, The mass of vanadium V is calculated as an atomic percentage. In the S2.3 atomic ratio-mass ratio conversion, the standard atomic masses of vanadium are 50.94 g / mol, those of titanium are 47.87 g / mol, and those of nickel are 58.69 g / mol. In the S2.4 mixing process design, the particle size range of the mixed alloy is ≤200 micrometers, and the deviation range of the mixing uniformity test is the deviation between the actual content of any alloy element at any sampling point and the theoretical design value is ≤±3%.

12. The method for preparing a V-Ti-Ni shape memory alloy with high vanadium (V) content according to claim 3, characterized in that, The method S3. raw material pretreatment includes: S3.2 Surface pretreatment includes pickling, mechanical polishing and ultrasonic cleaning. The ultrasonic cleaning frequency is 40 kHz, the ultrasonic cleaning time is 10 min, and the drying temperature is 70℃-100℃. In S3.3 Proportioning Conversion and Weighing, the internal molar ratio of the V-Ni pre-alloy is V:Ni = 1:

2. Therefore, the formula for deducting the amount of pure Ni feed is: Firstly, the molar conversion of vanadium mass to molars is as follows: in, The molar mass of vanadium is approximately 50.94 g / mol. Secondly, according to the molar ratio, the corresponding number of nickel moles in the pre-alloy is: Third, the molar mass of nickel ≈58.69 g / mol, the mass of nickel inherent in the pre-alloy is: Fourth, the deduction for pure nickel (Ni) input is as follows: Fifth, the final amount of pure nickel actually weighed out is: ； In S3.5 packaging and storage, the packaging and storage environment is relative humidity <5% and storage temperature is 20℃—25℃.

13. The method for preparing a V-Ti-Ni shape memory alloy with high vanadium (V) content according to claim 4, characterized in that, The method S4, vacuum induction furnace melting and ingot casting, includes: S4.1 Raw materials are charged into the furnace in the following order: nickel (Ni) → V-Ni pre-alloyed → titanium (Ti). The amount of raw materials charged accounts for 60%-70% of the furnace cavity volume. S4.2 In the vacuum pumping and preheating process, the vacuum degree is 1 x 10 -2 Pa, the vacuum pumping time is 5 min - 15 min, and the low-temperature preheating temperature of the charging is ≤ 300℃. -3 Pa, the vacuum pumping time is 5 min - 15 min, and the low-temperature preheating temperature of the charging is ≤ 300℃. In S4.3, during induction heating and melting homogenization, the temperature range of the segmented power gradient is 1300℃-1450℃, and the holding time is 25min. In S4.4 Atmosphere switching and argon protection, the purity of high-purity argon is ≥99.999%, and a positive pressure protective atmosphere of 0.05MPa-0.1MPa is established.

14. The method for preparing a V-Ti-Ni shape memory alloy with high vanadium (V) content according to claim 5, characterized in that, The method S5. billet trimming and heating homogenization includes: In the S5.1 billet peeling and finishing process, the dimensional tolerance of the finished billet shall be ≤ ±0.5%, and the processing stress shall be ≤ 10% of the billet yield strength. In the S5.2 billet loading and heating process, a segmented heating program is adopted, which is divided into a preheating section of 200℃ / h, a medium-speed section of 100℃ / h, and a final speed section of 50℃ / h, with a heating range of 800℃-950℃. In the S5.3 heat preservation treatment, the temperature range is 800℃-950℃, and the heat preservation time is 30min-150min; The cooling method is either slow cooling or isothermal cooling; The slow cooling rate is 5℃ / min; The isothermal cooling rate is to first hold the temperature at 600℃ for 60 minutes, and then cool it down at a constant rate of 10℃ / min to room temperature of 25℃.

15. The method for preparing a V-Ti-Ni shape memory alloy with high vanadium (V) content according to claim 6, characterized in that, The method S6. hot forging includes: S6.1 In the blank trimming process, the dimensional tolerance of the trimmed blank shall be ≤ ±0.5%, and the temperature range for heat preservation or insulation shall be 300℃—400℃; S6.2 During the preheating of the billet before hot forging, the heating range is 800℃-950℃, and the segmented heating is divided into three stages: a preheating stage of 200℃ / h, with a temperature of room temperature to 400℃; a medium-speed stage of 100℃ / h, with a temperature of room temperature to 400-800℃; and a final-speed stage of 50℃ / h, with a temperature of room temperature to 800-950℃. The holding time under inert atmosphere protection is 30min-150min. In S6.3 hot forging deformation, the final forging temperature is 650℃-700℃; the forging speed is 5mm / s-20mm / s; the forging pressure is 100MPa-250MPa; and the cross-sectional area reduction is ≥30%.

16. The method for preparing a V-Ti-Ni shape memory alloy with high vanadium (V) content according to claim 7, characterized in that, The method S7. The first hot rolling includes: In the S7.1 billet heating process, the heating temperature is 800℃-950℃, the heating rate is 5℃ / min-15℃ / min, and the holding time under argon protection is 30 min-120 min. In S7.2 rolled bar billet, the rolling speed is 0.1m / s-1.0m / s, the deformation per pass is 10%-20%, the cumulative cross-sectional area reduction is ≥30%, and the hot rolling temperature is 850℃-950℃; In S7.3, during the cooling and inspection after hot rolling, the probe frequency for ultrasonic testing is 5MHz-10MHz, and the cooling rate is 5℃ / min-20℃ / min.

17. The method for preparing a V-Ti-Ni shape memory alloy with high vanadium (V) content according to claim 8, characterized in that, The method S8. The second hot rolling includes: In the S8.1 billet heating process, the heating rate is 5℃ / min—15℃ / min, the heating temperature range is 800℃—950℃, the temperature uniformity deviation in the furnace is ≤±10℃, and the holding temperature range is 30min—120min. In S8.2 rolling, the rolling speed is 0.05 m / s to 0.5 m / s, the roll gap adjustment accuracy is ≤0.05 mm, the roll pressure uniformity is ≤5%, the total number of passes in multi-pass hot rolling is 3 to 10, the deformation per pass is 8% to 15%, the cumulative reduction rate of multiple passes is ≥30%, the rolling temperature is 850℃ to 950℃, and the rolling zone temperature setting is within ±10℃. In S8.3 Wire cooling and quality inspection, the cooling rate is 5℃ / min—20℃ / min, and the ultrasonic testing frequency range is 2MHz—10MHz.

18. The method for preparing a V-Ti-Ni shape memory alloy with high vanadium (V) content according to claim 9, characterized in that, In S9.2, the installation and parameter setting of the drawing equipment are as follows: the drawing speed is 0.5m / min to 3m / min, the drawing die hole diameter accuracy is ≤ ±0.005mm, and the drawing tension is 50MPa to 150MPa. In the S9.3 cold drawing operation, the single reduction rate during the cold drawing process is 3%-8%, the cumulative reduction rate is ≥15%, and the tension fluctuation is ≤5%. S9.4 In finished product inspection and packaging, the tolerance for wire diameter is ≤ ±0.01mm.

19. A V-Ti-Ni shape memory alloy material with high vanadium (V) content obtained by the preparation method according to claims 1-18, characterized in that, The V-Ti-Ni shape memory alloy material has the following composition by atomic percentage: The ratio of titanium to nickel is Ti:Ni = 49.3:50.7; High vanadium content, with vanadium content ranging from 1 to 5 at.

20. The V-Ti-Ni shape memory alloy material with high vanadium (V) content according to claim 19, characterized in that, The optimal composition of the V-Ti-Ni shape memory alloy material, by atomic percentage, is as follows: V2Ti 48.3 Ni 49.7 The shape memory filament has a titanium to nickel ratio of 48.3:49.7, a vanadium content of 2 at%, and a filament size of 8–20 μm. V5Ti 46.8 Ni 48.2 The shape memory filament has a titanium to nickel ratio of 46.8:48.2, a vanadium content of 5 at%, and a filament size of 5-12 μm. V1Ti 48.8 Ni 50.2 The shape memory filament has a titanium to nickel ratio of 48.8:50.2 and a vanadium content of 1 at%, with a filament size of 10-25 μm. V3Ti 47.8 Ni 49.2 The shape memory filament has a titanium to nickel ratio of 47.8:49.2 and a vanadium content of 3 at%, with a filament size of 8–18 μm.

21. The V-Ti-Ni shape memory alloy material with high vanadium (V) content according to claim 19, characterized in that, The V-Ti-Ni shape memory alloy material mainly includes the following phases: The high-temperature austenitic B2 phase is the matrix phase of Ni-Ti shape memory alloys, forming an ordered body-centered cubic structure and exhibiting reversible phase transformation properties. The low-temperature monoclinic martensitic phase B19' is the low-temperature phase of shape memory alloys. It transforms from the B2 phase through martensitic phase transformation to form a monoclinic crystal structure, exhibiting alloy shape memory effect and superelastic properties. The vanadium-rich V second phase is a reinforcing phase of shape memory alloys. The uniform distribution of the second phase can refine the grains and contains intermetallic compounds such as Ni3V and Ti2NiV.

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