Titanium-zirconium-niobium-tin shape memory alloy and method for producing the same

Abstract

The present disclosure relates to the technical field of shape memory alloys, and particularly relates to a titanium-zirconium-niobium-tin shape memory alloy and a preparation method thereof. In the alloy proportioning design, the method adds sufficient tin in a titanium-zirconium-niobium matrix (infinite solid solution), and forms a supersaturated titanium-zirconium-niobium-tin alloy through solid solution heat treatment, and then performs aging heat treatment above the alpha to beta phase transition temperature, avoids precipitation of brittle phases such as alpha phase or omega phase, and precipitates a zirconium-rich second phase, realizes strengthening of the parent phase, and improves superelasticity function.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of shape memory alloys, in particular to a titanium-zirconium-niobium-tin shape memory alloy and a preparation method thereof. BACKGROUND

[0002] Shape Memory Alloys (SMA) are a kind of advanced metal intelligent materials, which have the ability to restore to the original shape after being subjected to temperature or pressure changes. At different temperatures, the alloy can exhibit different crystal structures, and the reversible phase transition between these structures makes the alloy exhibit unique properties.

[0003] CN 102345035A, published on February 8, 2012, discloses a production process of a titanium-nickel shape memory alloy material, which has excellent shape memory function and superelasticity, but the nickel content is high and nickel ions have certain sensitization to the human body, which greatly limits the application of titanium-nickel shape memory alloy in the body.

[0004] Nickel-free titanium-based shape memory alloys are strong candidates to replace titanium-nickel alloys, especially metastable titanium-zirconium-niobium-tin shape memory alloys, which have attracted more and more attention from researchers due to their better biocompatibility and large recoverable strain. However, the superelastic stress of the solid solution heat treated titanium-zirconium-niobium-tin alloy is low, which hinders its commercial application.

[0005] Traditional aging strengthening methods, such as using aging heat treatment to precipitate alpha phase or omega phase or alpha+omega double phase in the solid solution heat treated titanium-zirconium-niobium-tin alloy, can strengthen the parent phase and improve the superelastic stress of the alloy, but often damage the plasticity of the alloy and easily cause brittle fracture.

[0006] It can be seen that the problem of how to improve the superelastic stress of the alloy while maintaining the plasticity of the shape memory alloy in the prior art is a difficult problem that needs to be solved by those skilled in the art. SUMMARY

[0007] Based on the above discussion, in order to improve or solve the problem of how to improve the superelastic stress of the alloy while maintaining the plasticity of the shape memory alloy mentioned above, the present application develops a titanium-zirconium-niobium-tin shape memory alloy and a preparation method thereof, which comprises the following steps:

[0008] S1, configuring raw materials according to the atomic percentage of the titanium-zirconium-niobium-tin alloy;

[0009] S2, vacuum melting the raw materials configured in step S1 to obtain a button-shaped alloy ingot;

[0010] S3, the alloy ingot prepared in step S2 is ultrasonically cleaned, dried, homogenized at high temperature, and quenched;

[0011] S4, the homogenized alloy ingot obtained in step S3 is cut into an alloy blank, and cold-rolled along the length direction at room temperature;

[0012] S5, the alloy cut in step S4 is surface polished, ultrasonically cleaned, dried, vacuum solid-solution heat treated, and quenched after the treatment;

[0013] S6, the alloy after the solid-solution heat treatment obtained in step S5 is surface polished, ultrasonically cleaned, dried, vacuum aging heat treated, and quenched after the treatment, to obtain a zirconium-rich precipitated titanium-zirconium-niobium-tin shape memory alloy.

[0014] In an embodiment, preferably, in step S5, the specific step of the vacuum solid-solution heat treatment is as follows: the vacuum degree of a container tube is (1.0-1.5)×10 -3 Pa, the furnace temperature of a heat treatment furnace is adjusted to 1000-1200℃, after the furnace temperature is stabilized, the container tube containing the alloy is put into the furnace, and the heat treatment time is 0.5-2h, so that the vacuum solid-solution heat treatment is completed.

[0015] In an embodiment, preferably, in step S6, the specific step of the vacuum aging heat treatment is as follows: the vacuum degree of a container tube is (1.0-1.5)×10 -3 Pa, the aging heat treatment is performed in a heat treatment furnace, the treatment temperature is 650-700℃, and the treatment time is 1-100h.

[0016] In an embodiment, preferably, in step S1, the atomic percentage of the titanium-zirconium-niobium-tin alloy is zirconium (Zr): 15-20at%, niobium (Nb): 9-12at%, tin (Sn): 4-6at%, and the balance is titanium.

[0017] In an embodiment, preferably, in step S1, the purity of the titanium metal particles is 99.8-99.999%; the purity of the zirconium metal particles is 99.8-99.95%; the purity of the niobium metal sheet is 99.8-99.99%, and the length×width×height is (5-6)×(5-5.5)×(0.1-0.3)mm; and the purity of the tin metal particles is 99.8-99.99%.

[0018] Nb metal sheet thickness higher than 0.3mm value may adversely affect the preparation process of titanium-zirconium-niobium-tin alloy, in particular: when the thickness of Nb metal sheet is too high, due to the high melting point of Nb metal, it is not easy to be melted in the heating melting process, which may lead to uneven distribution of alloy composition, affect the microstructure of the alloy, thereby reducing the overall strength and toughness of the alloy.

[0019] In an embodiment, preferably, in step S2, the pure metal titanium ingot as the oxygen absorber is melted before melting, the melting vacuum degree is (1.0-1.5)×10 -3 Pa, the melting time is 2.5-3.0min, and after melting, the furnace washing operation is performed, and the step is repeated 6-8 times, and finally the weight of the button-shaped alloy ingot is 25-30g. The furnace washing operation can be performed by using the existing scheme, which can achieve the purpose of removing impurities.

[0020] In an embodiment, preferably, in step S3, the furnace temperature of the heat treatment furnace is adjusted to 1200-1400℃ in the container tube with a vacuum degree of (1.0-1.5)×10 -3 Pa, and after the furnace temperature is stabilized, the container tube containing the alloy ingot is placed into the furnace, and the homogenization heat treatment time is 4-8h.

[0021] In an embodiment, preferably, in steps S3, S5 and S6, the ultrasonic cleaning is performed by using anhydrous alcohol, and after the cleaning is completed, an ice water bath is used for quenching.

[0022] In an embodiment, more preferably, in steps S3, S5 and S6, the container tube is a quartz tube, and the heat treatment furnace is a tube type heat treatment furnace.

[0023] In an embodiment, preferably, in step S4, the alloy blank with a length, width and height of (15-20)×(10-15)×(8-10)mm 3 is cut from the homogenization heat treated alloy ingot, the cold rolling reduction rate is 90-95%, and the final thickness of the cold rolled plate is 0.2-0.3mm.

[0024] The application also provides a titanium-zirconium-niobium-tin shape memory alloy prepared by the preparation method.

[0025] Beneficial effects: the application provides a titanium-zirconium-niobium-tin shape memory alloy preparation method. In the alloy ratio design, the method can strengthen the parent phase, improve the shape memory ability of the alloy at high temperature, improve the overall mechanical properties, durability and thermal stability of the alloy, and also can ensure the plasticity of the alloy and improve the superelasticity function of the alloy.

[0026] In the preferred scheme of the present application, the cold-rolled alloy is treated by vacuum solution heat treatment, and the specific vacuum degree is (1.0-1.5) x 10 -3 Pa, the temperature is 1000-1200℃, and the treatment time is 0.5-2h; the vacuum solution heat treatment adopted in the present application makes the solute atoms in the alloy dissolve into the matrix to form a supersaturated solid solution. This treatment can promote the uniform distribution of alloying elements and eliminate the stress generated by cold and hot working, so that the alloy recrystallizes.

[0027] In the further scheme of the present application, the alloy after the vacuum solution heat treatment is treated by vacuum aging heat treatment, and the specific vacuum degree is (1.0-1.5) x 10 -3 Pa, the temperature is 650-700℃, and the treatment time is 1-100h; the vacuum aging heat treatment adopted in the present application makes the supersaturated solid solution precipitate at a proper temperature to form fine and dispersed second phase particles, thereby enhancing the mechanical properties of the alloy. The present application takes advantage of the strong affinity of zirconium to tin, and the zirconium-tin atom pair with equal atomic ratio has the lowest mixing enthalpy (-43kJ / mol), which can precipitate zirconium-rich second phase from the supersaturated titanium-zirconium-niobium-tin alloy at the temperature of the present application, while avoiding the precipitation of brittle phases such as alpha phase, omega phase or alpha+omega dual phase.

[0028] More preferably, the alloy after the combination of the vacuum solution heat treatment and the vacuum aging heat treatment can fully exploit the potential of the shape memory alloy and improve the performance of the alloy. The solution treatment ensures the uniform distribution of alloying elements and the elimination of local stress, while the aging treatment further enhances the mechanical properties and memory effect of the alloy. This combined process can regulate the microstructure of the alloy to achieve the most suitable structure and performance matching, thereby exhibiting excellent shape memory ability and super-elasticity in macroscopic performance. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is the cyclic tensile stress-strain curve of the solution heat treated and aging heat treated alloy at room temperature.

[0030] Figure 2 is the backscattered electron image of the solution heat treated and aging heat treated alloy.

[0031] Figure 3 is the electron selected area diffraction pattern of the transmission electron microscope of the aging heat treated alloy. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments; the technical features designed in different implementation modes of the present invention described below can be combined with each other as long as they do not conflict with each other; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0033] In the description of the present invention, it should be noted that all terms used in the present invention (including technical terms and scientific terms) have the same meanings as those generally understood by ordinary technicians in the field to which the present invention belongs, and should not be understood as limiting the present invention; it should be further understood that the terms used in the present invention should be understood to have meanings consistent with the meanings of these terms in the context of this specification and in the relevant fields, and should not be understood in an idealized or overly formal sense, unless explicitly defined as such in the present invention.

[0034] In order to demonstrate that the method provided by the present invention for strengthening a metastable nickel-free titanium-zirconium-niobium-tin shape memory alloy using a zirconium-rich precipitate phase has outstanding technical effects compared with the prior art, the present invention will be further described in detail in combination with the following examples and comparative examples.

[0035] According to the above test method, the present invention provides the following embodiments:

[0036] Example 1

[0037] 1. Alloy Preparation

[0038] The raw materials titanium metal particles (purity: 99.999%), zirconium metal particles (purity: 99.95%), niobium metal sheets (purity: 99.99%, size: 5×5×0.3mm) and tin metal particles (purity: 99.99%) are arranged according to atomic percentage (Zr: 20at%, Nb: 9at%, Sn: 5at%, and the remainder is titanium).

[0039] The raw materials are placed in a vacuum of (1.0-1.5)×10 -3 Pa vacuum arc melting furnace, before melting, pure metal titanium ingot as oxygen absorber is melted, and the melting vacuum degree is (1.0-1.5)×10 -3 Pa, the smelting time is 2.5-3.0min, and the furnace is washed after smelting. This step is repeated 6 times to finally obtain a button-shaped alloy ingot weighing 25-30g.

[0040] 2. Homogenization heat treatment

[0041] The prepared alloy ingot was ultrasonically cleaned with anhydrous alcohol (for 10 minutes), dried, and then vacuum-sealed in a quartz tube with a vacuum of (1.0-1.5) x 10 -3 Pa. The temperature of the tube furnace was adjusted to 1200°C, and after the temperature was stabilized, the quartz tube containing the alloy ingot was placed in the furnace, and the homogenization heat treatment was performed for 6 hours. After the homogenization heat treatment, the quartz tube was broken in an ice water bath to quench the alloy.

[0042] 3. Cold rolling

[0043] An alloy blank with dimensions of 20 (length) x 10 (width) x 10 (height) mm 3 was cut from the homogenized alloy ingot, and cold-rolled in the length direction at a cold rolling reduction of 90-95%, with a final thickness of 0.2-0.3 mm.

[0044] 4. Solution heat treatment

[0045] An alloy blank with the desired dimensions was cut from the cold-rolled sheet, and the surface was mechanically polished and then ultrasonically cleaned with anhydrous alcohol (for 10 minutes). The alloy was vacuum-sealed in a quartz tube with a vacuum of (1.0-1.5) x 10 -3 Pa. The temperature of the tube furnace was adjusted to 1000°C, and after the temperature was stabilized, the quartz tube containing the alloy was placed in the furnace, and the solution heat treatment was performed for 30 minutes. After the solution heat treatment, the quartz tube was broken in an ice water bath to quench the alloy.

[0046] 5. Aging heat treatment

[0047] The surface of the solution heat treated alloy was mechanically polished and then ultrasonically cleaned with anhydrous alcohol (for 10 minutes). The alloy was vacuum-sealed in a quartz tube with a vacuum of (1.0-1.5) x 10 -3 Pa. The temperature of the tube furnace was adjusted to 700°C, and after the temperature was stabilized, the quartz tube containing the alloy was placed in the furnace, and the aging heat treatment was performed for 50 hours. After the aging heat treatment, the quartz tube was broken in an ice water bath to quench the alloy.

[0048] A titanium-zirconium-niobium-tin shape memory alloy was obtained.

[0049] Example 2

[0050] This example is different from Example 1 in that the temperature of the aging heat treatment in Step 5 was 600°C, and the aging heat treatment was performed for 50 hours. The other steps were the same as in Example 1.

[0051] Example 3

[0052] The difference between this embodiment and embodiment 1 is that the temperature of the aging heat treatment in step 5 is 700° C. and the aging heat treatment time is 20 hours. The other steps are the same as those in embodiment 1.

[0053] Comparative Example 1

[0054] The present invention also provides the following comparative example 1: the difference from Example 1 is that comparative example 1 does not adopt the vacuum aging heat treatment in step 5, but the alloy is subjected to solution heat treatment, and other conditions remain the same as Example 1.

[0055] Comparative Example 2:

[0056] Comparative Example 2 is a technical solution of the patent application with publication number CN 116254430 A. The composition and ratio of the alloy in the technical solution are Zr: 18at%, Nb: 11at%, Sn: 3at%, and the balance is titanium. Comparative Example 2 uses existing technology to prepare the alloy. The preparation method specifically includes:

[0057] 1. Ti, Zr, Nb, and Sn metal raw materials with a purity higher than 99.9% are configured according to the following ratios: Zr: 18 at%, Nb: 11 at%, Sn: 3 at%, and the remainder being the atomic percentage of titanium.

[0058] 2. Place the raw materials prepared in step 1 into a high vacuum arc melting furnace for melting. First, draw the vacuum degree to 1×10 -2 Pa, and then introduce high-purity Ar gas for purge and repeat several times, and then draw the vacuum degree to 3×10 -3 Pa below, preparing the raw materials for smelting. Before smelting the raw materials, high-purity titanium ingots are melted and cooled in a high-purity Ar gas protective environment to remove residual oxygen in the furnace. To ensure the compositional uniformity of the alloy ingots, the raw materials are turned at least four times during the smelting process, and magnetic stirring is applied during the smelting process. During the alloy smelting process, the smelting furnace is cooled by circulating water at a temperature of 20°C.

[0059] 3. The alloy ingot obtained in step 2 was sealed in a high-purity Ar gas protection environment, and then placed in a box-type annealing furnace preheated to 1000°C for annealing for 2 hours;

[0060] 4. The alloy ingot that has completed the annealing treatment in step 3 is subjected to rapid quenching treatment in ice salt water.

[0061] The titanium-zirconium-niobium-tin shape memory alloy of Comparative Example 2 was finally obtained.

[0062] The difference between Comparative Example 2 and Example 1 is that the process of preparing the alloy in Comparative Example 2 does not use the solid solution heat treatment and vacuum aging heat treatment steps.

[0063] The above examples and comparative examples were subjected to corresponding tests, and the test methods (standards) were as follows:

[0064] Vickers hardness test: the Vickers hardness testing equipment was a Vickers microhardness tester (model HV-1000Z), the test load was 1 kgf, and the test load holding time was 10 s.

[0065] Tensile test: the tensile testing equipment was a high-low temperature tensile testing machine (model CMT1104GD), the sample gauge length was 30 mm, the tensile direction was parallel to the rolling direction, and the tensile rate was 1.67 x 10 -4 s -1 .

[0066] The results are shown in the following table:

[0067] Table 1 below is a comparison of titanium-zirconium-niobium-tin shape memory alloys prepared by Examples 1-3 and Comparative Examples 1-2.

[0068] Table 1

[0069] Yield strength / MPa Vickers hardness / Hv Strain at break / % Superelastic recovery strain / % Example 1 633 300 13 4.5 Example 2 500 255 17 3.0 Example 3 420 230 20 2.5 Comparative Example 1 370 225 25 0.1 Comparative Example 2 300 218 22 0.5

[0070] Compared with Comparative Example 1 and Comparative Example 2, the titanium-zirconium-niobium-tin shape memory alloy provided by Example 1-3 has a significantly improved yield strength and superelastic recovery strain. As can be seen from the above experimental tests and comparisons, Example 1 has the highest hardness value and yield strength, and maintains a certain breaking strain and a higher superelastic recovery strain.

[0071] Comparative Example 1 (solution heat treated alloy) and Example 1 (age heat treated alloy) were subjected to cyclic tensile stress-strain tests and backscattered electron imaging, as shown in Figure 1 and Figure 2 .

[0072] Figure 1 The cyclic tensile stress-strain curves of Comparative Example 1 and Example 1 at room temperature are shown. The results show that the age alloy has a significant superelastic behavior and a significantly improved superelastic stress compared with the solution alloy (no superelastic behavior). This indicates that the method of precipitating a zirconium-rich second phase from the saturated titanium-zirconium-niobium-tin alloy can strengthen the parent phase and thus improve the superelasticity.

[0073] Figure 2 The backscattered electron images of the solution heat treated and age heat treated alloys are shown, and the results are as follows: Figure 2It can be seen that the alloy in solid solution state does not contain second phase in the matrix, which indicates that tin element is completely solid-solved into the matrix to form a supersaturated alloy. And, according to the results of X-ray energy spectrum (EDS) analysis, the contents of titanium, zirconium, niobium and tin in the matrix (atomic percentage, at%) are relatively small compared with the configured alloy composition (Zr: 20 at%, Nb: 9 at%, Sn: 5 at%, and the balance is titanium), which realizes the successful preparation of the alloy. After aging heat treatment, white zirconium-rich second phase is precipitated in the matrix, but no α phase is observed.

[0074] Figure 3 The electron selected area diffraction pattern of the alloy after aging heat treatment is shown. It can be seen that no ω precipitated phase is observed in the matrix of the alloy sample.

[0075] Therefore, by designing the alloy ratio and heat treatment process parameters, the method avoids the precipitation of α phase and ω phase, and improves the superelasticity of the alloy by precipitating zirconium-rich second phase.

[0076] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a titanium-zirconium-niobium-tin shape memory alloy, characterized in that: The steps include: S1. preparing raw materials according to the atomic percentage of titanium-zirconium-niobium-tin alloy; S2, vacuum melting the raw materials prepared in step S1 to obtain button-shaped alloy ingots; S3, ultrasonically cleaning the alloy ingot prepared in step S2, drying it, homogenizing it at high temperature, and then quenching it; S4, cutting alloy billets from the homogenized heat-treated alloy ingot obtained in step S3, and cold rolling them along the length direction at room temperature; S5, polishing the surface of the alloy intercepted in step S4, ultrasonic cleaning, drying, vacuum solution heat treatment, and quenching after treatment; S6, polishing the surface of the solution heat treated alloy obtained in step S5, ultrasonically cleaning it, drying it, performing vacuum aging heat treatment, and quenching it after treatment to obtain a zirconium-rich precipitated titanium-zirconium-niobium-tin shape memory alloy; Step S5, the specific steps of the vacuum solution heat treatment are: in a vacuum degree of (1.0-1.5)×10 -3 Pa container tube, adjust the temperature of the heat treatment furnace to 1000-1200 ° C, after the furnace temperature stabilizes, place the container tube containing the alloy into the furnace, and heat treatment time is 0.5-2 h, that is, complete vacuum solution heat treatment; In step S6, the specific steps of the vacuum aging heat treatment are: in a vacuum degree of (1.0-1.5)×10 -3 Pa container tube, and perform aging heat treatment in a heat treatment furnace at a temperature of 650-700°C for a treatment time of 1-100 h.

2. The method for preparing a titanium-zirconium-niobium-tin shape memory alloy according to claim 1, characterized in that: In step S1, the atomic percentage of the titanium-zirconium-niobium-tin alloy is zirconium: 15-20 at%, niobium: 9-12 at%, tin: 4-6 at%, and the balance is titanium.

3. The method for preparing a titanium-zirconium-niobium-tin shape memory alloy according to claim 1, characterized in that: In step S1, the purity of the titanium metal particles is 99.8-99.999%; the purity of the zirconium metal particles is 99.8-99.95%; the purity of the niobium metal sheet is 99.8-99.99%, and the length × width × height are (5-6) × (5-5.5) × (0.1-0.3) mm. 3 ;The purity of tin metal particles is 99.8-99.99%.

4. The method for preparing a titanium-zirconium-niobium-tin shape memory alloy according to claim 1, characterized in that: In step S2, the pure metal titanium ingot as an oxygen absorber is melted before smelting, and the melting vacuum degree is (1.0-1.5)×10 -3 Pa, the smelting time is 2.5-3.0 min, and the furnace is cleaned after smelting. This step is repeated 6-8 times to obtain an alloy ingot.

5. The method for preparing a titanium-zirconium-niobium-tin shape memory alloy according to claim 1, characterized in that: In step S3, the homogenization heat treatment is specifically performed as follows: at a vacuum degree of (1.0-1.5)×10 -3 Pa container tube, adjust the furnace temperature of the heat treatment furnace to 1200-1400℃, and after the furnace temperature stabilizes, place the container tube containing the alloy ingot into the furnace, and the treatment time is 4-8 hours.

6. The method for preparing a titanium-zirconium-niobium-tin shape memory alloy according to claim 1, characterized in that: The ultrasonic cleaning is performed using anhydrous alcohol, and then quenched in an ice water bath.

7. The method for preparing a titanium-zirconium-niobium-tin shape memory alloy according to claim 1, characterized in that: In the step S4, a piece of metal having a length, width and height of (15-20) × (10-15) × (8-10) mm is cut from the alloy ingot subjected to homogenization heat treatment. 3 The alloy billet has a cold rolling reduction rate of 90-95% and the final thickness of the cold rolled sheet is 0.2-0.3mm.

8. A titanium-zirconium-niobium-tin shape memory alloy prepared according to the preparation method according to any one of claims 1 to 7.

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