Microstructure and performance optimized TiNiCuNb alloy and preparation method thereof

Abstract

The invention discloses a TiNiCuNb alloy with an optimized microscopic structure and performance and a preparation method of the TiNiCuNb alloy, and belongs to the technical field of functional materials. According to the TiNiCuNb alloy and the preparation method thereof, the problems that the macroscopic surface of an existing TiNiCuNb alloy is prone to cracks, and precipitated phases and interface microscopic cracks exist in an alloy microscopic structure are solved. The invention provides an alloy with a thermoelastic effect, wherein the chemical formula of the alloy is (Ti54Ni34Cu12) 100-xNbx. According to the method, high-vacuum arc melting, progressive rolling heat treatment and heat preservation between rolling passes are adopted, the content and distribution of a second phase are regulated and controlled through the multi-temperature heat treatment process, the phase transition temperature and the elastic heat effect of the alloy are effectively regulated and controlled, meanwhile, the defects of macrocracks, microcracks and the like occurring in the rolling process of the alloy are reduced, and the alloy quality is improved. And the shape memory alloy plate which is free of macroscopic and microscopic structure defects, good in plasticity, narrow in phase change lag, good in phase change cycle stability and good in elastic heat effect is obtained.

Description

Technical Field

[0001] The present invention relates to a TiNiCuNb alloy with optimized microstructure and properties and a preparation method thereof, belonging to the technical field of functional materials. Background Art

[0002] TiNi shape memory alloy has excellent shape memory effect and superelasticity, and has broad application prospects in the fields of aerospace, shipbuilding, biomedicine, etc. The functional characteristics of shape memory alloy mainly come from the thermoelastic martensitic transformation. The alloy deforms in the martensite state, and through heating, the martensite→austenite transformation can be realized, and the deformation is recovered, so as to realize the shape memory effect. In the austenite state, the alloy obtains superelastic deformation through stress-induced austenite→martensite transformation. After unloading the stress, the deformation is recovered, showing elastic deformation superior to that of ordinary alloys. Since the austenite→martensite transformation belongs to a first-order phase transformation, latent heat will occur during the phase transformation process. Therefore, under the action of external stress, the shape memory alloy realizes the elastocaloric effect through stress-induced martensitic transformation and inverse transformation, and is expected to use the elastocaloric effect of the alloy for refrigeration, so as to replace the current compression refrigeration method and obtain a low-emission and low-cost refrigeration technology.

[0003] At present, TiNi shape memory alloy is mainly prepared into bulk materials by high-vacuum melting technology. It is found that dislocations are introduced during the cyclic heating-cooling process of the alloy, resulting in the drift of the martensitic transformation 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 transformation thermal hysteresis of the alloy. However, when the content of Cu is high, the alloy shows great brittleness. After further doping with Nb element, the plasticity of the alloy is improved, and the narrow phase transformation hysteresis characteristic of the alloy is retained. At the same time, the cyclic stability of the phase transformation temperature can be further improved by the introduction of β-Nb phase in the alloy.

[0004] However, at present, TiNiCuNb alloy is mainly prepared by melting, suction casting or ordinary rolling methods, and there are problems such as cracks easily appearing on the macroscopic surface of the alloy, precipitation phases and interfacial microcracks existing in the microstructure of the alloy, and the elastocaloric effect is not obvious, which is not conducive to the practical application of the alloy. Therefore, developing a TiNiCuNb alloy with no macroscopic and microscopic defects, good plasticity, narrow phase transformation hysteresis, good phase transformation cyclic stability and elastocaloric effect is an important prerequisite for realizing the application of TiNiCuNb alloy. Summary of the Invention

[0005] The present invention aims to solve the above problems existing in the existing TiNiCuNb alloy with elastocaloric effect, and provides a TiNiCuNb shape memory alloy sheet having no macroscopic and microscopic defects, good plasticity, narrow phase transformation hysteresis, good phase transformation cycle stability and elastocaloric effect, and a preparation method thereof.

[0006] The technical solution of the present invention:

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

[0008] Further defined, the thickness of the alloy is 1 - 1.2 mm.

[0009] Another objective of the present invention is to provide a preparation method for the above TiNiCuNb alloy with optimized microstructure and properties. The method includes the following steps:

[0010] (1) Weigh high-purity Ti, Ni, Cu, and Nb metal blocks as melting raw materials according to the atomic percentage of (Ti 54 Ni 34 Cu 12 ) 100-x Nb x , and melt them in a high-vacuum arc melting furnace to obtain a button-shaped alloy ingot;

[0011] (2) After the first heat treatment of the button-shaped alloy ingot, perform progressive rolling on a rolling mill, and perform the second heat treatment once every two rolling treatments until a sheet with a thickness of 1 - 1.2 mm is obtained. Stop rolling, and anneal the obtained rolled alloy to obtain a TiNiCuNb alloy with optimized microstructure and properties.

[0012] Further defined, the melting conditions are: vacuum to 6×10 -6 Pa, the melting current is 200 - 1000 A, and flip melting is performed more than 8 times.

[0013] Further defined, the temperature of the first heat treatment is 800 - 950 °C, and the holding time is 1 - 3 h.

[0014] Further defined, the temperature of the second heat treatment is 800 - 950 °C, and the holding time is 3 - 10 min.

[0015] Further defined, the annealing treatment temperature is 300 - 700 °C, and the holding time is 4 - 10 h.

[0016] It is further defined that the annealing process is performed in a sealed vacuum quartz tube.

[0017] It is further defined that the progressive rolling processing conditions are: the first rolling pressure is 0.06 mm, then the rolling is increased by 0.02 to 0.04 mm each time until the pressure is 0.24 to 0.30 mm, and then the rolling is continued by maintaining the pressure of 0.24 to 0.30 mm each time until the thickness of the plate is 1 to 1.2 mm.

[0018] A third object of the present invention is to provide an application of the TiNiCuNb alloy with optimized microstructure and performance, specifically, to use the alloy as a solid refrigerant.

[0019] Beneficial effects of the present invention:

[0020] The present invention provides a chemical formula (Ti 54 Ni 34 Cu 12 ) 100-x Nb x The invention discloses an alloy plate with optimized microstructure and performance, wherein 0≤x≤20. The TiNiCuNb alloy plate with optimized microstructure and performance is prepared by high vacuum arc melting and progressive rolling heat treatment. The progressive rolling heat treatment includes progressive rolling deformation and insulation process between rolling passes. The progressive rolling deformation can start with a small deformation of the second phase and gradually increase the deformation amount, so as to prevent micro cracking caused by the mismatch between the second phase and the matrix deformation. The internal stress and dislocation strengthening generated by the previous rolling deformation can be weakened by insulation between passes, so as to facilitate the next rolling deformation. After rolling, the content and distribution of the second phase are regulated by a multi-temperature heat treatment process, which effectively regulates the alloy phase transition temperature, further reduces the defects such as internal stress and micro cracks in the alloy during the rolling process, and makes the Nb-rich second phase produce preferential orientation, so as to obtain a TiNiCuNb shape memory alloy plate with no macro and micro structural defects, good plasticity, narrow phase transition hysteresis, good phase transition cycle stability and elastic-thermal effect. In addition, the preparation method of the alloy plate with elastic-caloric effect provided by the present invention has the advantages of simple process, high production efficiency, good repeatability, low cost, etc., which is conducive to realizing industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a photo of the button-shaped alloy ingot prepared in Example 1;

[0022] Figure 2 This is a photo of the rolled alloy plate prepared in Example 1;

[0023] Figure 3Metallographic structure photograph of the as-rolled alloy sheet prepared in Example 1;

[0024] Figure 4 SEM photographs and EDS result diagrams of the as-rolled alloy sheet prepared in Example 1 at different magnifications;

[0025] Figure 5 DSC cycle curve comparison diagrams of the as-rolled alloy sheet prepared in Example 1 with different numbers of cycles;

[0026] Figure 6 Tensile stress-strain curve comparison diagrams of the annealed alloy sheets prepared in Example 2 and Example 3;

[0027] Figure 7 SEM photographs of the fracture of the as-rolled alloy sheet prepared in Example 1 at different magnifications;

[0028] Figure 8 Diagram of the elastocaloric effect test results of the annealed alloy sheet prepared in Example 3. Detailed implementation manners

[0029] To make the above objects, features, and advantages of the present invention more apparent and understandable, the following detailed description of the specific implementation manners of the present invention will be given in conjunction with the embodiments of the specification.

[0030] Many specific details are set forth in the following description to facilitate a thorough understanding of the present invention. However, the present invention may be implemented in other ways different from those described herein. Those skilled in the art can make similar generalizations without departing from the spirit of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0031] Secondly, the so-called "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation manner 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 separate or alternative embodiment that excludes other embodiments.

[0032] The experimental methods used in the following embodiments are all conventional methods unless otherwise specified. The materials, reagents, methods, and instruments used, unless otherwise specified, are all conventional materials, reagents, methods, and instruments in the art, and those skilled in the art can obtain them through commercial channels.

[0033] Example 1

[0034] The structural formula of the as-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 preparation method of the as-rolled alloy sheet includes the following steps:

[0036] First, calculate the mass of each metal element according to the atomic ratio of the metal elements, select Ti, Ni, Cu, and Nb metal blocks with a purity of 99.9% as the melting raw materials, and carry out melting in a high-vacuum arc melting furnace under argon protection. The melting conditions are: vacuum to 6×10 -6 Pa, the melting current is 500 A, and the melting is flipped 8 times to ensure uniform alloy composition, and then cooled to obtain a button-shaped alloy ingot, as Figure 1 shown.

[0037] Then, keep the obtained button-shaped alloy ingot at 850 °C for 1 h, and then roll it on a rolling mill. The rolling temperature is 850 °C, the reduction in the first rolling is 0.06 mm, and then it is rolled with an increase of 0.02 mm each time until the reduction reaches 0.24 mm. After that, continue to roll with a reduction of 0.24 mm each time until the thickness of the sheet reaches 1.2 mm and stop rolling. And during two adjacent rollings, the sample is put back into the heat treatment furnace and kept at 850 °C for 4 min to ensure uniform temperature of the sample for the next rolling, and an as-rolled alloy sheet is obtained, as Figure 2 shown.

[0038] Characterize the morphology of the obtained as-rolled alloy sheet.

[0039] Figure 3 is the metallographic structure photo of the above as-rolled alloy sheet. It can be seen from Figure 3 that in the low-magnification metallographic structure photo, the alloy shows a dense and uniform two-phase distribution, indicating that an alloy block without microdefects and with a uniform overall tissue distribution can be obtained by progressive rolling heat treatment.

[0040] Figure 4 are the SEM photos and EDS result diagrams of the above as-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 as-rolled alloy sheet, indicating that the progressive rolling method can effectively avoid local cracking of the alloy during rolling. Further, according to the microstructure morphology and EDS test results, the as-rolled alloy sheet is mainly composed of Nb-rich phase and TiNiCu matrix. The Nb-rich phase shows a preferred orientation along the rolling direction, and the interface between the Nb-rich phase and the matrix is well bonded without defects such as microcracks. And the dark dot-like Ti2(NiCu) phase was also observed ( Figure 4 where A, B, and C in

[0041] Figure 5 point to the TiNiCu matrix, Nb-rich phase, and Ti2(NiCu) phase respectively). Figure 5 Figure is a comparison chart of DSC cycle curves of the as-rolled alloy sheet prepared above with different cycle numbers, and the cycle numbers are 1 time, 10 times, and 60 times respectively. It can be seen from

[0042] Figure 7 that after multiple cycles, the martensitic transformation temperature and latent heat of the alloy basically did not change, showing good cycle stability.

[0043] Example 2

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

[0045] Example 3

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

[0047] Figure 6 Figure is the tensile stress-strain curves of the as-rolled alloy sheet prepared in Example 1 and the annealed alloy sheets prepared in Example 2 and Example 3. It can be seen from the figure that the stress platform of stress-induced martensitic transformation of the alloy increases after annealing, and the superelastic strain increases somewhat.

[0048] Figure 8 Figure shows the elastocaloric effect of the annealed alloy sheet prepared in Example 3. Specifically, it was loaded at a loading rate of 100 N / min to 500 MPa and then immediately unloaded, and the loading-unloading was carried out 3 times, and the curve of temperature changing with time was recorded. It can be seen from Figure 8 that during the loading process, the temperature of the alloy increased by about 2 °C, and during the unloading process, the surface temperature of the alloy decreased by about 5 °C, showing an obvious elastocaloric effect.

[0049] The above are only the preferred embodiments of the present invention. Considering that those skilled in the art to which the present invention pertains can make appropriate changes and modifications to the above-described embodiments, therefore, 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 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, x represents the atomic percentage content.

2. The TiNiCuNb alloy with optimized microstructure and properties according to claim 1, characterized in that: The alloy thickness is 1 to 1.2 mm.

3. A method for preparing the TiNiCuNb alloy with optimized microstructure and properties as claimed in claim 1, characterized in that: include: (1) According to (Ti 54 Ni 34 Cu 12 ) 100-x Nb x Weigh high-purity Ti, Ni, Cu, and Nb metal blocks as smelting raw materials, and smelt them in a high vacuum arc melting furnace to obtain button-shaped alloy ingots; (2) After the button-shaped alloy ingot is subjected to a first heat treatment, it is subjected to a progressive rolling treatment on a rolling mill, and a second heat treatment is performed after every two rolling treatments until a plate with a thickness of 1 to 1.2 mm is obtained. The rolling is stopped, and the obtained rolled alloy is annealed to obtain a TiNiCuNb alloy with optimized microstructure and properties.

4. The preparation method according to claim 3, characterized in that: Melting conditions: vacuum to 6×10 -6 Pa, the melting current is 200 ~ 1000A, and the melting is turned over more than 8 times.

5. The preparation method according to claim 3, characterized in that: The first heat treatment temperature is 800-950° C., and the insulation time is 1-3 hours.

6. The preparation method according to claim 3, characterized in that: The second heat treatment temperature is 800-950°C, and the insulation time is 3-10 minutes.

7. The preparation method according to claim 3, characterized in that: The annealing temperature is 300-700°C and the holding time is 4-10h.

8. The preparation method according to claim 3 or 7, characterized in that: The annealing process is carried out in a sealed vacuum quartz tube.

9. The preparation method according to claim 3, characterized in that: The progressive rolling treatment conditions are as follows: the first rolling pressure is 0.06 mm, then the pressure is increased by 0.02 to 0.04 mm each time until the pressure is 0.24 to 0.30 mm, and then the rolling is continued with the pressure maintained at 0.24 to 0.30 mm each time until the thickness of the plate is 1 to 1.2 mm.

10. An application of the TiNiCuNb alloy with optimized microstructure and properties as claimed in claim 1 or 2, characterized in that: Used as a solid refrigerant.

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