A high-strength 3D printing nickel-titanium-iron shape memory alloy and its preparation method

Abstract

The present invention relates to the field of alloy additive technology, and more particularly to a high-strength 3D-printed nickel-titanium-iron shape memory alloy and a preparation method thereof. The alloy is prepared by this method. The method comprises constructing a thermodynamic database and combining solidification simulation with an open-source code library to search for the Pareto optimal solution set of the second phase Ti2Ni phase fraction and the crack sensitivity factor, thereby screening out the target component content of the alloy; first, smelting the alloy components with the target component content to obtain a nickel-titanium-iron alloy ingot, then atomizing the nickel-titanium-iron pre-alloy powder, vacuum-drying the screened nickel-titanium-iron pre-alloy powder to obtain a powder raw material of the alloy; and using a selective laser melting process to print the powder raw material layer by layer to obtain a 3D-printed nickel-titanium-iron shape memory alloy part entity. The present invention can produce a 3D-printed nickel-titanium-iron shape memory alloy with a low phase transition temperature, high mechanical properties, and good forming properties.

Description

Technical Field

[0001] The present invention relates to the field of alloy additive technology, and in particular to a high-strength 3D printing nickel-titanium-iron shape memory alloy and a preparation method thereof. Background Art

[0002] NiTi shape memory alloys possess properties such as a low phase transition temperature, excellent mechanical properties at room temperature, and high recovery stress at relatively low temperatures. Furthermore, compared to other low-temperature shape memory alloys, NiTi shape memory alloys offer significant advantages in stability and reliability when used in cryogenic environments. For example, NiTi shape memory alloy pipe fittings have been widely used in aircraft hydraulic piping systems and are one of the most typical and successful examples of shape memory alloy applications in engineering.

[0003] Due to the high ductility of nickel-titanium-based shape memory alloys and the high work hardening during machining, they present machining challenges such as material cracking, surface peeling, and tearing during machining. Laser 3D printing technology, which has emerged in recent years, relies on computer-aided design (such as CAD-aided design) to obtain the three-dimensional structural information of complex parts. It directly prepares solid parts with complex structures through a layer-by-layer accumulation method, effectively solving the machining challenges of nickel-titanium-based shape memory alloys. Among them, the complex structure solid parts prepared by selective laser melting technology have good surface finish and high geometric accuracy, and are currently the main 3D printing technology for preparing nickel-titanium-based shape memory alloys.

[0004] However, the high cooling rate, repeated remelting, and complex thermal history of the selective laser melting technique lead to uneven microstructure, high residual stress, and metallurgical defects in the 3D-printed nickel-titanium shape memory alloy, thus affecting the overall performance of the alloy. Furthermore, the strong lattice distortion caused by the addition of the third component, iron, further increases the tendency of nickel-titanium shape memory alloy to solidify and crack, deteriorating the forming properties of the 3D-printed nickel-titanium alloy.

[0005] Currently, 3D printed nickel-titanium-iron shape memory alloys typically use a relatively low iron content (atomic ratio <1 at.%). However, the alloy has a high phase transition temperature, far from meeting actual service requirements. If a 3D printed nickel-titanium-iron shape memory alloy uses a higher iron content (atomic ratio ≥2 at.%), it is prone to severe solidification cracking and delamination, significantly reducing its mechanical properties and even causing molding failure. Therefore, it is necessary to develop a high-strength 3D printed nickel-titanium-iron shape memory alloy and its preparation method to solve the problems of high phase transition temperature, low mechanical properties and poor molding in existing 3D printed nickel-titanium-iron shape memory alloys. Summary of the Invention

[0006] The present invention aims to provide a high-strength 3D printing nickel-titanium-iron shape memory alloy and a preparation method thereof. The specific technical solutions are as follows:

[0007] In a first aspect, the present invention provides a method for preparing a high-strength 3D printed nickel-titanium-iron shape memory alloy, comprising:

[0008] Step S1: Based on the phase equilibrium data of nickel-titanium-iron system in existing literature, a thermodynamic database of nickel-titanium-iron ternary system with rich nickel-titanium end is established; solidification simulation is performed on nickel-titanium-iron alloys with a wide range of alloy compositions in the thermodynamic database, and the variation relationship between the second phase fraction and the crack sensitivity factor of the nickel-titanium-iron alloys under different component contents is obtained with the help of a crack sensitivity factor model; using the variation relationship, an open source code library is used to search for the Pareto optimal solution set of the second phase Ti2Ni phase fraction and the crack sensitivity factor, and then the target component content of the 3D printed nickel-titanium-iron shape memory alloy is screened;

[0009] Step S2: First, a 3D printing nickel-titanium-iron shape memory alloy component with a target component content is smelted to obtain a nickel-titanium-iron alloy ingot, and then a nickel-titanium-iron pre-alloyed powder is prepared by gas atomization. The sieved nickel-titanium-iron pre-alloyed powder is vacuum-dried to obtain a powder raw material for 3D printing nickel-titanium-iron alloy;

[0010] Step S3: Printing the powder raw material layer by layer using a selective laser melting process to obtain a 3D printed nickel-titanium-iron shape memory alloy part entity.

[0011] Optionally, the mass percentage of each component in the wide alloy composition range is as follows: 43-50 wt.% titanium, 0.01-4 wt.% iron, and the balance nickel.

[0012] Optionally, the atomization method is an electrode induction atomization method.

[0013] Optionally, the sieved nickel-titanium-iron pre-alloyed powder has a particle size of 15 to 53 μm and a sphericity greater than 95%.

[0014] Optionally, the parameters adopted in the selective laser melting forming process include a laser power of 80-200 W, a scanning speed of 300-1000 mm / s, a scanning pitch of 60-90 μm, a spot diameter of 40-80 μm, and a powder layer thickness of 20-40 μm;

[0015] The selective laser melting forming process adopts a scanning strategy of strip partitioning and interlayer rotation. The strip width of the laser scanning is 4-6 mm, and the laser performs reciprocating scanning in each strip. The initial angle of the laser scanning of the first layer is set to 0°-60°, specifically 0° or 57°. The interlayer rotation angle of the laser scanning is 0°-90°, specifically 0°, 45°, 67° or 90°.

[0016] Optionally, before printing on the substrate using the selective laser melting process, the substrate is preheated to a substrate temperature of 180-200°C, an inert gas is filled to reduce the oxygen content in the working chamber to below 200 ppm, and the air pressure in the working chamber is maintained at 10-20 mbar greater than the atmospheric pressure.

[0017] Optionally, step S4 post-processing is also included; specifically, after completing the selective laser melting forming process, the heating of the substrate is turned off, the introduction of inert gas is stopped, the air pressure in the working chamber is reduced, and after the temperature of the substrate drops below 70°C, the remaining powder is cleaned and recovered, and the substrate with the part entity is taken out; after the substrate with the printed part is subjected to stress relief annealing, the part entity is separated from the substrate by wire cutting.

[0018] Optionally, the stress relief annealing includes heating the temperature to 150-200° C. at a rate of 5-10° C. / min for stress relief annealing, keeping the temperature for 3-5 hours, and then air cooling to room temperature.

[0019] Optionally, the step S4 further includes using sandpaper to polish and remove an oxide layer generated on the surface of the part entity after wire cutting.

[0020] In a second aspect, the present invention provides a high-strength 3D-printed nickel-titanium-iron shape memory alloy, which is prepared using the method for preparing the high-strength 3D-printed nickel-titanium-iron shape memory alloy; the target component content of the 3D-printed nickel-titanium-iron shape memory alloy includes the following mass percentages: 45.4 wt.% titanium, 2.2 wt.% iron, and the balance nickel.

[0021] The application of the technical solution of the present invention has at least the following beneficial effects:

[0022] (1) The present invention provides a method for preparing a high-strength 3D-printed nickel-titanium-iron shape memory alloy, which can prepare a 3D-printed nickel-titanium-iron shape memory alloy with a low phase transition temperature, high mechanical properties, and good forming properties. Specifically, in step S1, the present invention constructs a thermodynamic database, and combines solidification simulation and an open source code library to search for the Pareto optimal solution set of the second phase Ti2Ni phase fraction and the crack sensitivity factor, thereby efficiently screening the target component content of the 3D-printed nickel-titanium-iron shape memory alloy within a wide range of alloy components; the powder raw material obtained by step S2 of the 3D-printed nickel-titanium-iron shape memory alloy component with the target component content can be used to prepare a nickel-titanium-iron shape memory alloy with no surface cracks, good forming properties, high strength, and low phase transition temperature within a wide 3D printing process parameter window. Compared with the mixed powder formed by mechanically mixing nickel powder, titanium powder and iron powder (iron powder is more easily oxidized and easily introduces impurity oxygen elements), the present invention adopts the gas atomization method in the selective laser melting forming process to prepare the nickel-titanium-iron pre-alloyed powder, which is more uniform, has better powder fluidity and is not easy to introduce impurities, and can effectively avoid the cracking of the alloy in the 3D printing process caused by powder unevenness, impurity inclusions and poor fluidity.

[0023] (2) Compared with the traditional nickel-rich low-temperature nickel-titanium shape memory alloy, the target component content of the 3D printed nickel-titanium-iron shape memory alloy provided by the present invention limits the mass percentage of iron to 2.2 wt.% (i.e., the iron atomic ratio in the target component content is 2.1 at.%). The iron element at this content can increase the stability of the austenite phase in the 3D printed nickel-titanium-iron shape memory alloy, significantly reduce the phase transition temperature, and optimize the alloy solidification path by adjusting the relative content of nickel and titanium elements, so that the melt channel between the grains at the end of solidification is reduced, which facilitates the backfilling of the liquid phase melt, improves the liquid phase supply capacity and the overlap between the grains, thereby reducing the tendency of thermal cracking during the solidification process of the alloy and reducing the deterioration of the 3D printing forming performance caused by a higher iron content. In addition, at this target component content, the segregation of the brittle Ti2Ni phase at the grain boundary can be limited, and the generation of metallurgical defects (such as thermal cracks) can be reduced, thereby helping to improve the mechanical properties of the 3D printed nickel-titanium-iron alloy. Furthermore, the cost of iron is relatively low, and adding a higher content of iron can help reduce the raw material cost of 3D printed nickel-titanium-based shape memory alloys.

[0024] In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0026] Figure 1 The change of the second phase Ti2Ni phase fraction of the 3D printed nickel-titanium-iron shape memory alloy in Example 1 at different titanium contents and iron contents;

[0027] Figure 2 The change of crack sensitivity factor of the 3D printed nickel-titanium-iron shape memory alloy in Example 1 at different titanium and iron contents;

[0028] Figure 3 is a compression performance test curve of the 3D printed nickel-titanium-iron shape memory alloy in Example 5;

[0029] Figure 4 is the phase transformation curve of the 3D printed nickel-titanium-iron shape memory alloy in Example 5;

[0030] Figure 5 is the tensile property test curve of the 3D printed nickel-titanium-iron shape memory alloy in Example 6;

[0031] Figure 6 is a tensile property test curve of the 3D printed nickel-titanium-iron shape memory alloy in Example 7;

[0032] Figure 7 is a tensile property test curve of the 3D printed nickel-titanium-iron shape memory alloy in Example 8;

[0033] Figure 8 is a tensile property test curve of the 3D printed nickel-titanium-iron shape memory alloy in Example 9;

[0034] Figure 9 This is a tensile performance test curve of the 3D printed nickel-titanium-iron shape memory alloy in comparative example 1. DETAILED DESCRIPTION

[0035] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention are within the scope of protection of the present invention.

[0036] Example 1:

[0037] A method for preparing a high-strength 3D-printed nickel-titanium-iron shape memory alloy, comprising:

[0038] Step S1: Based on the phase equilibrium data of nickel-titanium-iron system in existing literature, a thermodynamic database of nickel-titanium-iron ternary system with rich nickel-titanium end is established using the Calphad method; solidification simulation of nickel-titanium-iron alloys with a wide range of alloy compositions in the thermodynamic database is performed using the Hill-Gulliver solidification simulation in Pandat software, and the relationship between the second phase fraction and the crack sensitivity factor of nickel-titanium-iron alloys with different composition contents is obtained using the Kou crack sensitivity factor model (see existing literature Kou S. A criterion for cracking during solidification. Acta Materialia 2015;88:366-74). Figure 1 and Figure 2 ; Using the change relationship, an open source code library is used to search for the Pareto optimal solution set of the second phase Ti2Ni phase fraction and the crack sensitivity factor (that is, the nickel-titanium-iron alloy component content when the second phase Ti2Ni phase fraction and the crack sensitivity factor simultaneously reach the Pareto minimum), and then the target component content of the 3D printed nickel-titanium-iron shape memory alloy is screened, specifically 45.4 wt.% titanium, 2.2 wt.% iron, and the remainder nickel; at this target component content, the segregation of the brittle Ti2Ni phase at the grain boundary can be limited, and the generation of metallurgical defects (such as thermal cracks) can be reduced, thereby helping to improve the mechanical properties of the 3D printed nickel-titanium-iron shape memory alloy;

[0039] Step S2: First, a 3D printing nickel-titanium-iron shape memory alloy component with a target component content is smelted to obtain a nickel-titanium-iron alloy cylindrical rod ingot, and then a nickel-titanium-iron pre-alloyed powder is prepared by a gas atomization method. The sieved nickel-titanium-iron pre-alloyed powder is vacuum-dried to obtain a powder raw material for 3D printing nickel-titanium-iron alloy;

[0040] Step S3: Printing the powder raw material layer by layer using a selective laser melting process to obtain a 3D printed nickel-titanium-iron shape memory alloy part entity.

[0041] The phase equilibrium data of the nickel-titanium-iron system includes the phase equilibrium data of pure component nickel, pure component titanium, pure component iron, binary nickel-titanium, binary nickel-iron, binary titanium-iron and ternary nickel-titanium-iron.

[0042] The phase equilibrium data of pure nickel, pure titanium, and pure iron are derived from the existing literature Dinsdale A. SGTEdata for pure elements. Calphad 1991;15:317-425.

[0043] The phase equilibrium data of binary nickel-titanium system is derived from the existing literature Povoden E, Cirstea D, Lang P,Wojcik T, Kozeschnik E. Thermodynamics of Ti–Ni shape memory alloys. Calphad2013;41:128-39.

[0044] The phase equilibrium data of the binary nickel-iron system comes from the existing literature Franke P, Seifert H. The influence of magnetic and chemical ordering on the phase diagram of Cr–Fe–Ni. Calphad 2011;35:148-54.

[0045] The phase equilibrium data of the binary titanium-iron system are derived from the existing literature Guo C, Li C, Zheng X, Du Z. Thermodynamic modeling of the Fe–Ti–V system. Calphad 2012;38:155-60.

[0046] The phase equilibrium data of the ternary nickel-titanium-iron system are derived from the existing literature De Keyzer J, Cacciamani G,Dupin N, Wollants P. Thermodynamic modeling and optimization of the Fe–Ni–Tisystem. Calphad 2009;33:109-23.

[0047] The mass percentages of the various components within the broad alloy composition range are as follows: titanium 43-50 wt.%, iron 0.01-4 wt.%, and the balance nickel.

[0048] The nickel-titanium-iron alloy ingots were purchased from Hunan Yuanji New Materials Co., Ltd.

[0049] The atomization method is an electrode-induced atomization method, which can effectively reduce the introduction of impurity elements such as carbon and oxygen, and meet the requirement of low impurity content of alloy powder in the SLM process. The specific process of electrode-induced atomization is as follows:

[0050] First, under a high-purity argon protective atmosphere (≥99.99%), the oxygen content of the entire atomization process was controlled below 500 ppm, and the nickel-titanium-iron alloy ingot was induction melted (melting temperature 1600°C, melting power 100 kW). Then, under an atomization pressure of 6 MPa, the molten nickel-titanium-iron metal melt passed through an alumina ceramic tube (nozzle aperture 3.5 mm), where it was broken into small droplets and quickly solidified into nickel-titanium-iron pre-alloyed powder. Finally, the obtained nickel-titanium-iron pre-alloyed powder was sieved and vacuum-dried to obtain the powder raw material for 3D printing nickel-titanium-iron alloy. The powder raw materials are calculated by mass percentage as follows: titanium 45.07%; iron 2.10%; carbon ≤0.03%; oxygen ≤0.08%, nitrogen ≤0.03%; copper ≤0.05%; aluminum ≤0.05%; manganese ≤0.05%; boron ≤0.05%; chromium ≤0.05%; nickel is the balance; the total of other elements is ≤0.10%; except for titanium, iron and nickel, the other elements are impurity elements introduced during the smelting, atomization and other processes.

[0051] The sieved nickel-titanium-iron pre-alloyed powder has a particle size of 15 to 53 μm and a sphericity greater than 95%.

[0052] The selective laser melting forming process includes debugging the 3D printing equipment, importing the three-dimensional slice model of nickel-titanium-iron alloy into the 3D printing equipment, and setting the printing process parameters and laser scanning strategy; preheating the substrate and filling it with argon gas to reduce the oxygen content in the working chamber, and then starting to print and form the nickel-titanium-iron shape memory alloy; after each printing of a powder layer thickness is completed, the substrate is lowered by one layer height, and a scraper re-flattens the nickel-titanium-iron alloy powder in the powder feeding chamber on the substrate, and the next powder layer is printed. This process is repeated to print the entire part entity layer by layer.

[0053] Specifically, the parameters used in the selective laser melting process include a laser power of 160 W, a scanning speed of 1000 mm / s, a scanning pitch of 80 μm, a spot diameter of 60 μm, and a powder layer thickness of 30 μm;

[0054] The selective laser melting forming process adopts a scanning strategy of strip partitioning and interlayer rotation. The strip width of the laser scanning is 4 mm. The laser performs reciprocating scanning in each strip. The initial angle of the first layer laser scanning is set to 57°. Thereafter, the interlayer rotation angle of the laser scanning is 67°.

[0055] Before printing on the substrate using the selective laser melting process, the forming chamber was evacuated to 10 -3After the 3D printing process, the pressure in the working chamber is maintained at 10-20 mbar above the ambient atmospheric pressure. High-purity argon is then introduced (>99.99%) for a protective atmosphere, repeated three times. Furthermore, to prevent warping and cracking at the bottom of the part, the substrate is preheated to 180°C, and a chamfer with a radius of 1 mm is provided at the bottom of the part. During the 3D printing process, the pressure in the working chamber is maintained at 10-20 mbar above the ambient atmospheric pressure. High-purity argon is then introduced to reduce the oxygen content in the working chamber to below 200 ppm. The part is placed at a 75° angle to the direction of the scraper's travel.

[0056] Step S4 post-processing; specifically, after completing the selective laser melting forming process, turn off the heating of the substrate, stop introducing the inert gas, reduce the air pressure in the working chamber, and after the temperature of the substrate drops below 70°C, clean and recover the residual powder, and take out the substrate with the part entity; after the substrate with the printed part is stress-relieved and annealed, separate the part entity from the substrate by electric spark wire cutting; immerse the part entity after wire cutting in epoxy resin for embedding and sealing to obtain a sample, and then use 400 mesh, 600 mesh, 800 mesh, 1200 mesh, 1500 mesh and 2000 mesh silicon carbide sandpaper to polish the embedded sample in sequence until the wire-cut oxide layer on the sample surface is removed and there are no obvious scratches, and then polish the sample using silica polishing liquid on a SAPHIR 520 automatic polishing machine.

[0057] The stress relief annealing was performed in a KSL-1200X box furnace by heating the temperature to 200° C. at a rate of 5° C. / min, and then air-cooling to room temperature after keeping the temperature for 4 hours.

[0058] Example 2:

[0059] Different from Example 1, the laser power is 80 W and the scanning speed is 300 mm / s.

[0060] Example 3:

[0061] Different from Example 1, the laser power is 200 W and the scanning speed is 1000 mm / s.

[0062] Example 4:

[0063] Different from Example 1, the laser power is 140 W and the scanning speed is 800 mm / s.

[0064] Using the selective laser melting process parameters (i.e., 3D printing process parameters) described in Examples 1-4, 3D-printed square NiTiFe shape memory alloy block parts, each measuring 8 mm × 8 mm × 8 mm (length × width × height), were produced. Each part in Examples 1-4 was tested for quality, and the test results are shown in Table 1. In Table 1, energy density = laser power / (scanning speed × scanning pitch × powder layer thickness), expressed in J / mm. 3 .

[0065] In the molding quality inspection, the surface crack detection method is as follows: First, the bottom surface and side surfaces of the 3D printed nickel-titanium-iron shape memory alloy part entity are ground and polished; then, the bottom surface and side surfaces of the part entity are observed using a LEICA DM4500P optical microscope to detect and record the surface crack conditions of the part entity.

[0066] The relative density test method is as follows: First, the dry weight W of the 3D printed nickel-titanium-iron shape memory alloy block part is measured using an electronic balance of model MSA324S-000-DU. 干燥 ; Then, immerse the part completely in distilled water and weigh its mass W after being placed in distilled water 水中 , and then according to Archimedes principle, the following formula ρ 合金 =ρ 水 ×W 干燥 / (W 干燥 -W 水中 ) Calculate the actual density of 3D printed NiTi shape memory alloy, while the theoretical density of 3D printed NiTi shape memory alloy is 6.45 g / cm 3 , which comes from the existing literature "Yuan B, Ge J, Chen H, Pan J, Zhang L,QiX. Printability and microstructure of Fe doped NiTi shape memory alloyfabricated by laser powder bed fusion. Mater Lett 2022;328:133099"; finally, the actual density is divided by the theoretical density to calculate the relative density of the 3D printed nickel-titanium-iron shape memory alloy block part.

[0067] The upper surface roughness detection method is as follows: the upper surface of the 3D printed nickel-titanium-iron shape memory alloy block part is scanned using a Contour GT-K optical profilometer to obtain the upper surface roughness of the part entity.

[0068] Table 1 Forming quality test results under different selective laser melting forming process parameters

[0069]

[0070] As shown in Table 1, Examples 1-4 of the present invention all produced 3D-printed NiTi shape memory alloys with crack-free surfaces and good molding quality. This indicates that the target composition content of the 3D-printed NiTi shape memory alloys selected by the present invention is applicable within a wide window of 3D printing process parameters.

[0071] Example 5:

[0072] The 3D printing process parameters described in Example 1 were used to prepare a 3D printed nickel-titanium-iron shape memory alloy rectangular block part entity with a size of 50 mm×10 mm×10 mm (length×width×height).

[0073] The compression performance test of the part prepared in Example 5 was conducted using an Instron 8804 electro-hydraulic servo test system. The test method was as follows: first, a cylindrical compression specimen with a diameter of 8 mm and a height of 10 mm was machined from the part prepared in Example 5 by wire-cutting. Subsequently, the surface of the cylindrical compression specimen was polished to remove the oxide layer generated during the wire-cutting process. Furthermore, a 1.6×10 -4 ·s -1 The cylindrical compression specimen was uniaxially compressed at a strain rate of , and the changes in stress and strain were recorded until the sample broke. Figure 3 The phase transformation behavior of the part prepared in Example 5 was tested by using a NETZSCH 204 differential scanning calorimeter. The test method was as follows: first, 15 mg of sample was taken, an empty aluminum crucible was used as a reference crucible, and the temperature was set at 10°C·min from room temperature. -1 The temperature was raised to 100 °C and kept at this temperature for 5 minutes; then, the temperature was raised to 100 °C min -1 The cooling rate was set at 100℃-150℃, and the heat absorption and release of the sample were recorded during the cooling process; then, the sample was cooled at 10℃·min -1 The heating rate is from -150℃ to 100℃, and the heat absorption and release of the sample during the heating process are recorded. The test is completed. Figure 4 .

[0074] See also Figure 3The nickel-titanium-iron shape memory alloy prepared in Example 5 exhibited a compressive strength of 2670 MPa and a compressive strain of 45%. Compared to the 3D-printed nickel-titanium-iron shape memory alloy with a compressive strength of 2156 MPa and a compressive strain of 35% reported in the existing literature (Yuan B, Ge J, Zhang L, Chen H, Wei L, Zhou Y, et al. Laserpowder bed fusion of NiTiFe shape memory alloy via pre-mixed powder: microstructural evolution, mechanical and functional properties. Rare Metals 2024;43:2300-16), the nickel-titanium-iron shape memory alloy prepared in Example 5 exhibited significantly improved compressive strength and compressive strain.

[0075] See also Figure 4 When the nickel-titanium-iron shape memory alloy prepared in Example 5 was cooled from 100°C to -150°C, no martensitic phase transformation was detected in the differential scanning calorimetry test, indicating that the martensitic phase transformation temperature is lower than -150°C. Compared with the existing literature (Xi R, Jiang H, Li G, Zhang Z, Zhao G, Vanmeensel K. et al. Effect ofFe addition on the microstructure, transformation behavior and superelasticity of NiTi alloys fabricated by laser powder bed fusion. VirtualPhys Prototyp 2022;18:2126376.), in which the martensitic phase transformation starting temperature of the 3D-printed nickel-titanium-iron alloy with an iron addition of 0.52 wt.% was as low as -50°C, the nickel-titanium-iron shape memory alloy with an iron addition of 2.2 wt.% in Example 5 has a lower martensitic phase transformation temperature.

[0076] The nickel-titanium-iron shape memory alloy prepared in Example 5 has a density of 99.2%, a surface roughness of 6.97 μm, and no surface cracks.

[0077] Example 6:

[0078] The difference from Example 1 is that the laser power is 180W, the scanning speed is 1000 mm / s, and the laser energy density is 83.3J / mm 3 .

[0079] Example 7:

[0080] The same 3D printing process parameters as in Example 1 were used.

[0081] Example 8:

[0082] The difference from Example 1 is that the laser power is 160W, the scanning speed is 900 mm / s, and the laser energy density is 74.1J / mm 3 .

[0083] 3D printing parameters described in Examples 6-8 were used to prepare rectangular NiTiFe shape memory alloy block parts with dimensions of 50 mm × 10 mm × 10 mm (length × width × height). Tensile properties of each part were tested using an MTS E44.104 electronic universal testing machine. The testing method was as follows: First, each part was processed by wire-cutting to produce a 15 mm, 2 mm gauge width, and 2 mm thickness I-shaped tensile specimen. Subsequently, the surface of the I-shaped tensile specimen was polished to remove the oxide layer generated during the wire-cutting process. Furthermore, the tensile strength of each I-shaped specimen was tested using a 1.6 × 10 -4 ·s -1 The strain rate of the I-shaped tensile specimen was uniaxially stretched and the changes in stress and strain were recorded until the sample broke. Figures 5 to 7 .

[0084] See also Figures 5 to 7 The tensile strength of the 3D printed nickel-titanium-iron shape memory alloy prepared in Example 6 is 895 MPa; the tensile strength of the 3D printed nickel-titanium-iron shape memory alloy prepared in Example 7 is 842 MPa; the tensile strength of the 3D printed nickel-titanium-iron shape memory alloy prepared in Example 8 is 915 MPa; compared with the existing literature (Xi R, Jiang H, Li G, Zhang Z, Zhao G, Vanmeensel K. et al. Effect of Fe addition on the microstructure, transformation behavior and superelasticity of NiTi alloys fabricated by laser powder bed fusion. Virtual Phys Prototyp 2022; 18: 2126376.), the tensile strength of the 3D printed nickel-titanium-iron shape memory alloys prepared in Examples 6 to 8 of the present invention are significantly higher than 736 MPa, showing excellent mechanical properties.

[0085] In addition, the 3D printed nickel-titanium-iron shape memory alloy prepared in Example 6 has a density of 99.6%, a surface roughness of 4.83 μm, and no surface cracks. The 3D printed nickel-titanium-iron shape memory alloy prepared in Example 7 has a density of 99.1%, a surface roughness of 6.44 μm, and no surface cracks. The 3D printed nickel-titanium-iron shape memory alloy prepared in Example 6 has a density of 99.5%, a surface roughness of 4.66 μm, and no surface cracks.

[0086] Example 9:

[0087] The difference from Example 1 is that the laser power is 140W, the scanning speed is 1000 mm / s, and the laser energy density is 58.3J / mm 3 .

[0088] Comparative Example 1:

[0089] Different from Example 9, step S3 and step S4 are eliminated, and the gas atomization method in step S2 is not adopted, and the nickel-titanium-iron alloy cylindrical rod ingot is directly obtained by smelting.

[0090] The 3D printing process parameters described in Example 9 and the ingot casting method of Comparative Example 1 were used to prepare rectangular block parts with dimensions of 50 mm × 10 mm × 10 mm (length × width × height). The tensile properties of each part were tested using an MTS E44.104 electronic universal testing machine. The testing method was as follows: First, each part was processed by wire-cutting to produce a 15 mm long, 2 mm wide, and 2 mm thick I-shaped tensile part; then, the surface of the I-shaped tensile part was polished to remove the oxide layer generated during the wire-cutting process; and then, the tensile strength of the I-shaped tensile part was tested using a 1.6 × 10 -4 ·s -1 The sample was uniaxially stretched at a strain rate of , and the changes in stress and strain were recorded until the sample broke. Figures 8 and 9 .

[0091] See also Figures 8 and 9 , the tensile strength of the nickel-titanium-iron alloy formed by the ingot casting scheme of Comparative Example 1 is 993 MPa, and the elongation is 1.15%. The 3D printed nickel-titanium-iron shape memory alloy prepared by Example 9 has a density of 99.8%, a surface roughness of 6.59 μm, a tensile strength of 1094 MPa, and an elongation of 3.21%. Compared with Comparative Example 1, the 3D printed nickel-titanium-iron shape memory alloy prepared by Example 9 has higher tensile strength, greater elongation, and excellent comprehensive mechanical properties. This proves that the 3D printed nickel-titanium-iron shape memory alloy prepared by the present invention has good forming performance and significantly improved mechanical properties.

[0092] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing high-strength 3D printing nickel-titanium-iron shape memory alloy, characterized in that: include: Step S1, establishing a thermodynamic database for a nickel-titanium-end nickel-titanium-iron ternary system; performing solidification simulation on nickel-titanium-iron alloys with a wide range of alloy compositions in the thermodynamic database, and obtaining a variation relationship between the second phase fraction and the crack sensitivity factor of the nickel-titanium-iron alloys at different component contents using a crack sensitivity factor model; utilizing the variation relationship, searching for a Pareto optimal solution set of the second phase fraction and the crack sensitivity factor using an open source code library, and then screening to obtain a target component content for 3D printing of nickel-titanium-iron shape memory alloys; the target component content of the 3D printing nickel-titanium-iron shape memory alloys includes the following mass percentages: 45.4 wt.% titanium, 2.2 wt.% iron, and the balance nickel; The mass percentages of the various components within the broad alloy composition range are as follows: titanium 43-50 wt.%, iron 0.01-4 wt.%, and the balance nickel; Step S2: First, a 3D printing nickel-titanium-iron shape memory alloy component with a target component content is smelted to obtain a nickel-titanium-iron alloy ingot, and then a nickel-titanium-iron pre-alloyed powder is prepared by gas atomization. The sieved nickel-titanium-iron pre-alloyed powder is vacuum-dried to obtain a powder raw material for 3D printing nickel-titanium-iron alloy; Step S3: Printing the powder raw material layer by layer using a selective laser melting process to obtain a 3D printed nickel-titanium-iron shape memory alloy part entity.

2. The method for preparing high-strength 3D printing nickel-titanium-iron shape memory alloy according to claim 1, characterized in that: The atomization method is an electrode induction atomization method.

3. The method for preparing high-strength 3D printing nickel-titanium-iron shape memory alloy according to claim 1, characterized in that: The sieved nickel-titanium-iron pre-alloyed powder has a particle size of 15 to 53 μm and a sphericity greater than 95%.

4. The method for preparing high-strength 3D printing nickel-titanium-iron shape memory alloy according to claim 1, characterized in that: The parameters used in the selective laser melting process include laser power of 80-200 W, scanning speed of 300-1000 mm / s, scanning spacing of 60-90 μm, spot diameter of 40-80 μm, and powder layer thickness of 20-40 μm. The selective laser melting process adopts a scanning strategy of strip partitioning and inter-layer rotation. The laser scanning strip width is 4-6 mm, and the laser scans back and forth in each strip. The initial angle of the first layer laser scanning is set to 0°~60°, and the inter-layer rotation angle of the laser scanning is set to 0°~90°.

5. The method for preparing high-strength 3D printing nickel-titanium-iron shape memory alloy according to claim 1, characterized in that: Before printing on a substrate using the selective laser melting process, the substrate is preheated to a temperature of 180-200°C, an inert gas is introduced to reduce the oxygen content in the working chamber to below 200 ppm, and the pressure in the working chamber is maintained at 10-20 mbar greater than atmospheric pressure.

6. The method for preparing high-strength 3D printing nickel-titanium-iron shape memory alloy according to claim 5, characterized in that: The method further includes post-processing step S4; specifically, after completing the selective laser melting process, turning off the heating of the substrate, stopping the introduction of inert gas, reducing the air pressure in the working chamber, and cleaning and recovering the remaining powder after the substrate temperature drops below 70°C, and taking out the substrate with the part entity; performing stress relief annealing on the substrate with the printed part, and then separating the part entity from the substrate by wire cutting.

7. The method for preparing high-strength 3D printing nickel-titanium-iron shape memory alloy according to claim 6, characterized in that: The stress relief annealing includes heating the material to 150-200° C. at a rate of 5-10° C. / min for stress relief annealing, keeping the temperature for 3-5 hours, and then air cooling the material to room temperature.

8. The method for preparing high-strength 3D printing nickel-titanium-iron shape memory alloy according to claim 6, characterized in that: The step S4 further includes using sandpaper to polish and remove the oxide layer generated on the surface of the part entity after the wire cutting.

9. A high-strength 3D printing nickel-titanium-iron shape memory alloy, characterized in that: The high-strength 3D printing nickel-titanium-iron shape memory alloy is prepared by the preparation method according to any one of claims 1 to 8.

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