A method for improving super-elasticity of beta titanium alloy by preparing sub-micron grains

Abstract

The application discloses a method for improving superelasticity of beta titanium alloy by preparing submicron grains, and first, a beta titanium alloy ingot is obtained by a vacuum argon arc melting method; a homogenization solid solution treatment is performed on the beta titanium alloy ingot to ensure that a single beta phase structure is obtained; then, a large deformation cold rolling treatment is performed on the treated beta titanium alloy ingot, and a cold rolling deformation amount is greater than 94%; finally, a low-temperature short-time solid solution treatment is performed on the alloy plate subjected to the large deformation cold rolling treatment, a solid solution treatment temperature is higher than a beta transformation temperature by 50-100 DEG C, and a solid solution treatment time is 150-200 s, so that the beta titanium alloy with submicron grains is obtained; the beta titanium alloy subjected to the large deformation cold rolling and the low-temperature short-time solid solution treatment has a submicron grain size, a minimum grain size is 0.3 microns, and a total recovery strain is up to 4.85%; and the beta titanium alloy is refined to the submicron level by the large deformation cold rolling and the low-temperature short-time solid solution treatment, so that the superelasticity of the beta titanium alloy is significantly improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metallurgy, and particularly relates to a method for improving super-elasticity of beta titanium alloy by preparing sub-micron grains. BACKGROUND

[0002] Beta titanium alloy has good biocompatibility and is a main load-bearing type of biological implant material, and is often used in dentistry, hip joint, stent, joint, bone plate, intramedullary nail, spine, etc. For beta titanium alloy, when an external stress is applied, alpha" (martensite) phase transition can occur above the martensite transformation temperature point, and when the external stress is removed, the shape of the alpha" reverse phase transition returns to the original state, which is called super-elasticity. Super-elasticity is widely used, on the one hand, it can play a buffering role when used as a human implant, and on the other hand, super-elasticity can also be used for orthodontic treatment. Ti-Ni-based alloy has good super-elasticity, but Ni + is easy to cause allergic reactions, so it is urgent to develop a nickel-free beta titanium alloy. At present, the developed Ti-Nb-based alloy has low yield strength, and twinning and dislocation slip are easy to open, which hinders the alpha" phase transition and its reverse change, resulting in weakening of super-elasticity, so it is an urgent problem to improve the super-elasticity of beta titanium alloy.

[0003] Fine-grain strengthening is a strengthening method for realizing the common improvement of strength and super-elasticity. Excessive grain size can cause uneven stress distribution of the grains, and dislocation slip is more likely to open, which can reduce the strength and weaken the super-elasticity of the material. Fine-grained grains can hinder dislocation movement, and dislocation slip is difficult to open, which increases the difficulty of plastic deformation of the material, and at the same time, fine-grained grains also reduce the size of alpha", which is beneficial to the alpha" phase transition and its reverse change, and significantly improves the super-elasticity of beta titanium alloy. Therefore, how to improve the super-elasticity of beta titanium alloy by fine-grained grains is a problem to be solved at present. SUMMARY

[0004] To solve the above technical problems, the purpose of the present application is to provide a method for improving the super-elasticity of beta titanium alloy by preparing sub-micron grains.

[0005] The technical scheme adopted by the present application is:

[0006] A method for improving the super-elasticity of beta titanium alloy by preparing sub-micron grains, specifically comprising the following steps:

[0007] Step 1, obtaining beta titanium alloy ingot by vacuum argon arc melting method, and uniformly treating the obtained beta titanium alloy ingot to ensure that a single beta phase structure is obtained, so as to facilitate subsequent large deformation cold rolling treatment;

[0008] Step 2, large deformation cold rolling is performed on the alloy ingot treated in step 1 to form fine grains, and alloy plate is obtained;

[0009] Step 3, low-temperature short-time solid solution treatment is performed on the alloy plate to control the growth of the as-rolled grains, and a beta titanium alloy with sub-micron grains is obtained.

[0010] Further, in step 1, the alloy elements are vacuum argon arc melted according to the proportion, in order to ensure the uniformity of the alloy composition, the beta titanium alloy ingot is flipped and remelted, and a beta titanium alloy ingot with uniform composition is obtained

[0011] Further, in step 1, the homogenization and solid solution treatment is performed at a vacuum degree less than 4*10 -3 Pa, at 950-1050℃ which is much higher than the beta phase transition temperature, for 2h heat treatment, and water cooling to room temperature.

[0012] Further, in step 2, the large deformation cold rolling is multi-pass rolling at room temperature, and the deformation amount is >94%.

[0013] Further, in step 3, the low-temperature short-time solid solution treatment is performed under argon protection, at 50-100℃ which is higher than the beta phase transition temperature, for 150-200s heat treatment, and then water cooling to room temperature.

[0014] Compared with the prior art, the present application has the following beneficial effects:

[0015] The design scheme ensures that a single beta phase structure is obtained by performing homogenization and solid solution treatment at 950-1050℃ which is much higher than the beta phase transition temperature after melting, so as to facilitate subsequent large deformation cold rolling treatment. Then, large deformation rolling is performed to introduce a large amount of dislocations and large deformation energy storage in the alloy plate, to provide recrystallization driving force for subsequent low-temperature short-time solid solution treatment, and to form fine grains. The temperature of the low-temperature short-time solid solution treatment is designed to be 50-100℃ which is higher than the beta phase transition temperature, to control the growth of the as-rolled grains, and finally obtain sub-micron level grains to significantly improve the superelasticity of the beta titanium alloy. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a phase diagram of the beta titanium alloy obtained by the method for improving the superelasticity of the beta titanium alloy by preparing sub-micron grains according to example 1 of the present application;

[0017] Figure 2 is a micro-morphology diagram of the beta titanium alloy obtained by the method for improving the superelasticity of the beta titanium alloy by preparing sub-micron grains according to example 1 of the present application;

[0018] Figure 3 is a grain size diagram of the beta titanium alloy obtained by the method for improving the superelasticity of the beta titanium alloy by preparing sub-micron grains according to example 1 of the present application;

[0019] Figure 4is a cyclic tensile curve of the beta titanium alloy obtained by the method for improving superelasticity of beta titanium alloy by preparing submicron grains according to the embodiment 1 of the present application;

[0020] Figure 5 is a microstructure morphology of the beta titanium alloy after deformation according to the comparative example 1 of the present application;

[0021] Figure 6 is a grain size diagram of the beta titanium alloy according to the comparative example 1 of the present application;

[0022] Figure 7 is a cyclic tensile curve of the beta titanium alloy according to the comparative example 1 of the present application. DETAILED DESCRIPTION

[0023] The present application will be described in detail below with specific examples in combination with the accompanying drawings.

[0024] A method for improving superelasticity of beta titanium alloy by preparing submicron grains, specifically comprising the following steps:

[0025] Step 1, obtaining beta titanium alloy ingot by vacuum argon arc melting method, and performing 950-1050℃ homogenization solid solution treatment on the obtained beta titanium alloy ingot to ensure obtaining single beta phase structure so as to facilitate subsequent large deformation cold rolling treatment;

[0026] Step 2, performing large deformation cold rolling on the beta titanium alloy ingot after step 1 to form fine grains, and obtaining alloy plate;

[0027] Step 3, performing low-temperature short-time solid solution treatment on the alloy plate under argon protection at a temperature higher than the phase transition temperature by 50-100℃, and the solid solution treatment time is 150-200s, and then water cooling to room temperature to obtain beta titanium alloy with submicron grains.

[0028] Step 4, performing cyclic loading tensile test on the sample after solid solution treatment with an interval of 1%.

[0029] Embodiment 1

[0030] The beta titanium alloy used is TiZrNbSn alloy, and the alloy composition is composed of the following atomic percentage components: 30% of Zr, 10% of Nb, 1% of Sn, and the balance of Ti and unavoidable impurities.

[0031] Step 1, according to the component selection, raw materials are selected, and Ti, Zr, Nb and Sn are vacuum argon arc melted according to the ratio, in order to ensure the composition uniformity of the TiZrNbSn alloy ingot, the TiZrNbSn alloy ingot is flipped and remelted, and the melting is performed for 7 times to obtain the TiZrNbSn alloy ingot with uniform composition. The TiZrNbSn alloy ingot is subjected to vacuum degassing at a vacuum degree less than 4×10 -3Pa is subjected to homogenization solution treatment at 980-1020℃ in the β phase region of TiZrNbSn alloy ingot for 2 hours to ensure a single β phase structure, which is convenient for large deformation cold rolling.

[0032] Step 2: The TiZrNbSn alloy ingot processed in Step 1 is cold rolled into a plate. The cold rolling process is carried out in multiple passes at room temperature until the deformation is 96%.

[0033] Step 3, as follows Figure 1 As shown in the phase diagram, the β transformation temperature (T) of this alloy βtrans The designed low-temperature short-time solution treatment temperature is 530–550℃, which is 50–100℃ higher than the β transformation temperature. Therefore, the alloy sheet obtained in step 2 is solution treated at 580–620℃ under argon protection, held for 180 seconds, and then water-cooled to room temperature to finally obtain a β-titanium alloy with submicron-sized particles. After the low-temperature short-time solution treatment, as shown... Figure 2 As shown, submicron-sized grains were formed. Figure 3 The statistical grain size diagram shows that the average grain size of the alloy is 0.6 μm and the minimum grain size is 0.3 μm.

[0034] Step 4: Perform cyclic loading tensile tests on the β-titanium alloy samples after solution treatment in Step 3 at 1% intervals. Figure 4 The figure shows the cyclic tensile curve of the alloy. The yield strength of the alloy is 350 MPa. With the increase of strain, at a strain of 5%, the total recovery strain (ε) r The maximum value is 4.85%. As can be seen from the above performance indicators, the process of large deformation rolling and low-temperature short-time solution treatment refines the β-titanium alloy grains to the submicron level, significantly improving its superelasticity.

[0035] Comparative Example 1

[0036] The β-titanium alloy used was a TiZrNbSn alloy, and its composition was the same as that in Example 1.

[0037] Step 1: Based on the composition, select raw materials and perform vacuum argon arc melting of Ti, Zr, Nb, and Sn according to the specified ratio. To ensure uniform alloy composition, the ingot is flipped and remelted seven times to obtain a β-titanium alloy ingot with uniform composition. The β-titanium alloy ingot is then melted under a vacuum degree less than 4 × 10⁻⁶. -3 Pa is subjected to homogenization solution treatment at 980–1020 °C, which is much higher than the β phase region of the alloy, for 2 hours to ensure that a single β phase structure is obtained, which is convenient for large deformation cold rolling.

[0038] Step 2: The β titanium alloy ingot processed in Step 1 is cold rolled into a plate. The cold rolling process is carried out in multiple passes at room temperature until the deformation is 96%.

[0039] Step 3: The β titanium alloy sheet obtained in Step 2 was solution treated at 880-920°C for 180s under argon atmosphere and then water cooled to room temperature. After solution treatment, the alloy formed larger grains, as shown in Fig. 1. Figure 5 Figure 6 The average grain size of the β titanium alloy was 26μm and the minimum grain size was 10μm.

[0040] Step 4: The sample after solution treatment in Step 3 was subjected to cyclic loading tensile test with 1% interval. Figure 7 The cyclic tensile curve of the β titanium alloy is shown in Fig. 2. The yield strength of the alloy was 195MPa, indicating that the increase of grain size reduced the resistance to plastic deformation. When the strain reached 5%, the total recovery strain (ε r ) was only 2.3%. It can be seen that the larger grain size reduced the superelasticity of the β titanium alloy.

[0041] The above embodiments only express the specific implementation of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be noted that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application. Therefore, the scope of protection of the present application should be subject to the appended claims.​

Claims

1. A method of improving superelasticity of a beta titanium alloy by preparing submicron grains, characterized by, Specifically comprising the following steps: Step 1, a beta titanium alloy ingot is obtained by a vacuum argon arc melting method, and homogenization solid solution treatment is performed on the obtained beta titanium alloy ingot to ensure that a single beta phase structure is obtained, thereby facilitating subsequent large deformation cold rolling treatment; Step 2, the beta titanium alloy ingot treated in step 1 is subjected to large deformation cold rolling to form fine grains, thereby obtaining an alloy plate, and the cold rolling process is multi-pass rolling at room temperature to a deformation amount > 94%; Step 3, the alloy plate is subjected to low-temperature short-time solid solution treatment, the low-temperature short-time solid solution treatment is performed under argon protection, the solid solution treatment temperature is 50-100 DEG C higher than the beta phase transition temperature, the solid solution treatment time is 150-200 s, and then water cooling to room temperature, the as-rolled grain growth is controlled, and a beta titanium alloy with submicron grains is obtained.

2. The method of improving super-elasticity of a β-titanium alloy by preparing sub-micron grains according to claim 1, characterized in that, In step 1, the alloy elements are vacuum argon arc melted according to the proportion, in order to ensure the uniformity of the alloy composition, the beta titanium alloy ingot is turned over and remelted, thereby obtaining a beta titanium alloy ingot with uniform composition.

3. The method of improving super-elasticity of a β-titanium alloy by preparing sub-micron grains according to claim 1, characterized in that, The homogenization solution treatment in Step 1 is performed at 950~1050°C for 2h heat treatment under a vacuum degree of less than 4x10 -3 Pa, and then water-cooled to room temperature.

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