Microstructure and performance optimized tini culb alloy and method of making

Abstract

The application discloses a TiNiCuNb alloy with optimized microstructure and performance and a preparation method thereof, and belongs to the technical field of functional materials. 54 Ni 34 Cu 12 ) 100‑x Nb x The application provides an alloy with a chemical formula of (Ti 54 Ni 34 Cu 12 ) 100‑x Nb x ) and a thermoelastic effect. The application adopts a high-vacuum arc smelting and gradual rolling heat treatment, a heat preservation method between rolling passes, controls the content and distribution of a second phase through a multi-temperature heat treatment process, effectively controls alloy phase transition temperature and the thermoelastic effect, reduces macroscopic cracks and micro cracks and other defects of the alloy in the rolling process, and obtains a shape memory alloy plate material with no macroscopic and microstructure defects, good plasticity, narrow phase transition hysteresis, good phase transition cycle stability and the thermoelastic effect.

Description

TECHNICAL FIELD

[0001] The present application relates to a microstructure and performance optimized TiNiCuNb alloy and a preparation method thereof, and belongs to the technical field of functional materials. BACKGROUND

[0002] TiNi shape memory alloy has excellent shape memory effect and super-elasticity, and has broad application prospects in the fields of aerospace, shipbuilding, biomedicine, etc. The functional characteristics of shape memory alloy mainly come from thermal-elastic martensitic phase transformation. The alloy is deformed in the martensitic state, and through heating, martensite to austenite transformation is realized, and the deformation is recovered, thereby realizing shape memory effect. In the austenitic state, the alloy obtains super-elastic deformation through stress-induced austenite to martensite phase transformation, and the deformation is recovered after unloading stress, showing elastic deformation better than ordinary alloys. Since the austenite to martensite transformation is a first-order phase transition, latent heat will occur during the phase transition. Therefore, under the action of external stress, shape memory alloy realizes the elastic-thermal effect through stress-induced martensitic phase transformation and reverse phase transformation, which is expected to utilize the elastic-thermal effect of the alloy for refrigeration, thereby replacing the current compressor refrigeration method and obtaining low-emission and low-cost refrigeration technology.

[0003] TiNi shape memory alloy is currently mainly prepared into bulk materials by high vacuum melting technology. It is found that in the process of cyclic heating-cooling, dislocations are introduced into the alloy, causing the drift of the martensitic phase transition temperature of the alloy, which is not conducive to the practical application of shape memory alloy. The performance of the alloy can be optimized by element doping. TiNiCuNb alloy is a quaternary TiNi-based shape memory alloy doped with Cu and Nb elements. The doping of Cu can reduce the phase transition hysteresis of the alloy, but when the content of Cu is high, the alloy shows great brittleness. After further doping of Nb element, the plasticity of the alloy is improved, and the narrow phase transition hysteresis characteristic of the alloy is retained. At the same time, the alloy can further improve the cyclic stability of the phase transition temperature through the introduction of β-Nb phase.

[0004] However, the current TiNiCuNb alloy is mainly prepared by melting, suction casting or ordinary rolling method, which has the problems of easy occurrence of cracks on the macroscopic surface of the alloy, existence of precipitated phase and interface microcracks in the microstructure of the alloy, and not obvious elastic-thermal effect, which is not conducive to the practical application of the alloy. Therefore, the development of TiNiCuNb alloy with no macroscopic and microstructure defects, good plasticity, narrow phase transition hysteresis, good phase transition cyclic stability and elastic-thermal effect is an important prerequisite for the application of TiNiCuNb alloy. SUMMARY

[0005] In order to solve the above-mentioned problems of existing TiNiCuNb alloys with elastothermal effect, this invention provides a TiNiCuNb shape memory alloy plate with no macroscopic and microscopic defects, good plasticity, narrow phase transformation hysteresis, good phase transformation cycle stability and elastothermal effect, and its preparation method.

[0006] The technical solution of this invention:

[0007] One objective of this invention is to provide a TiNiCuNb alloy with optimized microstructure and properties, the chemical formula of which is (Ti 54 Ni 34 Cu 12 ) 100-x Nb x , where 0≤x≤20, and x represents the atomic percentage content.

[0008] Further specified, the thickness of the alloy is 1 to 1.2 mm.

[0009] The second objective of this invention is to provide a method for preparing the aforementioned TiNiCuNb alloy with optimized microstructure and properties, the method comprising the following steps:

[0010] (1) According to (Ti 54 Ni 34 Cu 12 ) 100-x Nb x The percentage of atomic numbers is determined by weighing high-purity Ti, Ni, Cu, and Nb metal blocks as smelting raw materials, which are then smelted in a high-vacuum electric arc melting furnace to obtain button-shaped alloy ingots.

[0011] (2) After the button-shaped alloy ingot undergoes a first heat treatment, it is progressively rolled on a rolling mill, and a second heat treatment is performed after every two rolling processes until a plate with a thickness of 1 to 1.2 mm is obtained. Rolling is then stopped, and the resulting rolled alloy is annealed to obtain a TiNiCuNb alloy with microstructure and optimized properties.

[0012] Further specifying the smelting conditions: vacuum up to 6×10 -6 Pa, melting current of 200-1000A, and more than 8 inverted melting cycles.

[0013] Further specified, the first heat treatment temperature is 800-950℃, and the holding time is 1-3h.

[0014] Further specified, the second heat treatment temperature is 800-950℃, and the holding time is 3-10 min.

[0015] Further specified, the annealing temperature is 300–700℃, and the holding time is 4–10 hours.

[0016] Furthermore, the annealing process is carried out in a sealed vacuum quartz tube.

[0017] Further specifying the progressive rolling conditions, the first rolling pressure is 0.06 mm, then each rolling increment is 0.02 to 0.04 mm until a pressure of 0.24 to 0.30 mm is reached, and then rolling continues at a pressure of 0.24 to 0.30 mm until the thickness of the sheet is 1 to 1.2 mm.

[0018] The third objective of this invention is to provide an application of the TiNiCuNb alloy with the above-mentioned optimized microstructure and properties, specifically as a solid refrigerant.

[0019] Beneficial effects of this invention:

[0020] This invention provides a chemical formula (Ti) 54 Ni 34 Cu 12 ) 100-x Nb x TiNiCuNb alloy plates with optimized microstructure and properties, where 0≤x≤20, were prepared using high-vacuum arc melting and progressive rolling heat treatment. The progressive rolling heat treatment included progressive rolling deformation and inter-pass heat treatment. Progressive rolling deformation can start with small deformation of the second phase and gradually increase the deformation amount to prevent microcracks caused by the deformation mismatch between the second phase and the matrix. Inter-pass heat treatment can reduce the internal stress and dislocation strengthening generated by the previous rolling deformation, which is conducive to the next rolling deformation. After rolling, the content and distribution of the second phase are controlled by a multi-temperature heat treatment process, which effectively controls the phase transformation temperature of the alloy and further reduces defects such as internal stress and microcracks that occur in the alloy during rolling. It also causes the Nb-rich second phase to have a preferred orientation, resulting in a TiNiCuNb shape memory alloy plate with no macroscopic and microstructural defects, good plasticity, narrow phase transformation hysteresis, good phase transformation cycle stability and elastothermal effect. Furthermore, the method for preparing alloy plates with elastothermal effect provided by this invention has the advantages of simple process, high production efficiency, good repeatability and low cost, which is conducive to realizing industrial production. Attached Figure Description

[0021] Figure 1 A photograph of the button-shaped alloy ingot prepared in Example 1;

[0022] Figure 2 A photograph of the rolled alloy sheet prepared in Example 1;

[0023] Figure 3The image shows the metallographic structure of the rolled alloy sheet prepared in Example 1.

[0024] Figure 4 These are SEM images and EDS results of the rolled alloy sheet prepared in Example 1 at different magnifications.

[0025] Figure 5 A comparison of DSC cycle curves for different cycles of the rolled alloy sheet prepared in Example 1;

[0026] Figure 6 Comparison of tensile stress-strain curves of annealed alloy plates prepared in Examples 2 and 3;

[0027] Figure 7 These are SEM images of the fracture surface of the rolled alloy sheet prepared in Example 1 at different magnifications;

[0028] Figure 8 The figure shows the elasto-thermal effect test results of the annealed alloy sheet prepared in Example 3. Detailed Implementation

[0029] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0030] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0031] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0032] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0033] Example 1

[0034] The structural formula of the rolled alloy sheet provided in this embodiment is: (Ti 54 Ni 34 Cu 12 )90 Nb 10 .

[0035] The above structural formula is (Ti 54 Ni 34 Cu 12 ) 90 Nb 10 The method for preparing rolled alloy sheet includes the following steps:

[0036] First, the mass of each metal element was calculated according to its atomic ratio. Ti, Ni, Cu, and Nb metal blocks with a purity of 99.9% were selected as the smelting raw materials. Smelting was carried out in a high-vacuum electric arc furnace under argon protection. The smelting conditions were: vacuum to 6 × 10⁻⁶. -6 Pa, melting current of 500A, 8-fold inverted melting process to ensure uniform alloy composition, cooling, and obtaining button-shaped alloy ingots, such as Figure 1 As shown.

[0037] Then, the obtained button-shaped alloy ingot is held at 850℃ for 1 hour, and then rolled on a rolling mill at 850℃. The initial rolling reduction is 0.06 mm, and then each subsequent rolling increases by 0.02 mm until a reduction of 0.24 mm is reached. Rolling continues at a constant reduction of 0.24 mm until the plate thickness reaches 1.2 mm. Between adjacent rolling operations, the sample is returned to the heat treatment furnace and held at 850℃ for 4 minutes to ensure uniform temperature for the next rolling operation, resulting in a rolled alloy plate. Figure 2 As shown.

[0038] The morphology of the rolled alloy sheet obtained above was characterized.

[0039] Figure 3 The above-mentioned metallographic photographs of the alloy sheet in its rolled state are provided by [the relevant authority / organization]. Figure 3 It can be seen that the alloy shows a dense and uniform two-phase distribution in the low-magnification metallographic photograph, indicating that the alloy bulk material with no micro-defects and a uniform overall microstructure can be obtained by using progressive rolling heat treatment.

[0040] Figure 4 These are SEM images and EDS results of the rolled alloy sheet at different magnifications; combined with... Figure 2 and Figure 4It can be seen that no obvious cracks were observed on the surface of the rolled alloy sheet, indicating that the progressive rolling method can effectively avoid local cracking of the alloy during the rolling process. Further analysis of the microstructure and EDS test results shows that the rolled alloy sheet mainly consists of a Nb-rich phase and a TiNiCu matrix. The Nb-rich phase exhibits a preferred orientation along the rolling direction, and the interface between the Nb-rich phase and the matrix is ​​well-bonded, without any microcracks or other defects. Dark-colored dotted Ti2(NiCu) phases were also observed. Figure 4 In the diagram, A, B, and C refer to the TiNiCu matrix, the Nb-rich phase, and the Ti2(NiCu) phase, respectively.

[0041] Figure 5 This is a comparison of DSC cycle curves for the rolled alloy sheets prepared above at different cycle numbers: 1, 10, and 60 cycles. Figure 5 It can be seen that after multiple cycles, the martensitic transformation temperature and latent heat of the alloy remained basically unchanged, demonstrating good cycle stability.

[0042] Figure 7 The tensile fracture surface SEM images (at different magnifications) of the rolled alloy sheet prepared above show that it has a large number of dimples, which indicates that the rolled alloy sheet has good plasticity and toughness.

[0043] Example 2

[0044] The rolled alloy sheet prepared in Example 1 was encapsulated in a vacuum quartz tube and annealed at 500°C for 4 hours to obtain the annealed alloy sheet.

[0045] Example 3

[0046] The rolled alloy sheet prepared in Example 1 was encapsulated in a vacuum quartz tube and annealed at 700°C for 4 hours to obtain the annealed alloy sheet.

[0047] Figure 6 The figures show the tensile stress-strain curves of the rolled alloy sheet prepared in Example 1 and the annealed alloy sheets prepared in Examples 2 and 3. As can be seen from the figures, the stress plateau of the stress-induced martensitic phase transformation of the alloy increases after annealing, and the hyperelastic strain increases.

[0048] Figure 8 This describes the elasto-thermal effect of the annealed alloy sheet prepared in Example 3. Specifically, the sample was loaded at a rate of 100 N / min to 500 MPa and then immediately depressurized. This loading-unloading cycle was repeated three times, and the temperature change over time was recorded. Figure 8 It can be seen that the alloy temperature increases by about 2°C during loading and decreases by about 5°C during unloading, exhibiting a significant elasto-thermal effect.

[0049] The above description is only a preferred embodiment of the present invention. Given that those skilled in the art can make appropriate changes and modifications to the above embodiments, the present invention is not limited to the specific embodiments described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a TiNiCuNb alloy with optimized microstructure and properties, characterized in that, The chemical formula of the alloy plate is (Ti 54 Ni 34 Cu 12 ) 100-x Nb x , where 0≤x≤20, and x represents the atomic percentage content; Preparation methods include: (1) According to (Ti) 54 Ni 34 Cu 12 ) 100-x Nb x The percentage of atomic numbers is determined by weighing high-purity Ti, Ni, Cu, and Nb metal blocks as smelting raw materials, which are then smelted in a high-vacuum electric arc melting furnace to obtain button-shaped alloy ingots. (2) After the button-shaped alloy ingot undergoes the first heat treatment, it is subjected to progressive rolling on a rolling mill, and a second heat treatment is performed after every two rolling processes until a plate with a thickness of 1~1.2mm is obtained. Rolling is then stopped, and the resulting rolled alloy is annealed to obtain a TiNiCuNb alloy with microstructure and optimized performance. The progressive rolling conditions are as follows: the initial rolling pressure is 0.06 mm, and then the rolling is increased by 0.02~0.04 mm each time until the pressure reaches 0.24~0.30 mm. After that, the rolling continues with a pressure of 0.24~0.30 mm each time until the thickness of the plate is 1~1.2 mm.

2. The preparation method according to claim 1, characterized in that, The alloy has a thickness of 1~1.2mm.

3. The preparation method according to claim 1, characterized in that, The smelting conditions are: vacuum up to 6×10 -6 Pa, melting current of 200~1000A, and more than 8 inverted melting cycles.

4. The preparation method according to claim 1, characterized in that, The first heat treatment temperature is 800~950℃, and the holding time is 1~3h.

5. The preparation method according to claim 1, characterized in that, The second heat treatment temperature is 800~950℃, and the holding time is 3~10min.

6. The preparation method according to claim 1, characterized in that, The annealing temperature is 300~700℃, and the holding time is 4~10h.

7. The preparation method according to claim 1 or 6, characterized in that, The annealing process is carried out in a sealed vacuum quartz tube.

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