阅读说明：本技术 一种提高β钛合金超弹性的方法 (Method for improving superelasticity of beta titanium alloy ) 是由 潘艳 丁向东 孙巧艳 肖林 于 2019-09-30 设计创作，主要内容包括：本发明公开了一种提高β钛合金超弹性的方法,包括：选择具有形状记忆效应的块体β钛合金作为样品,根据样品的马氏体相变应变量,确定利于马氏体相变的位向；对样品进行电解抛光；对处理后的样品表面进行标记；对处理后的样品进行测试分析,获得样品的晶粒位向分布图；根据利于马氏体相变的位向,结合压痕标记及样品的晶粒位向分布图,确定利于马氏体相变的晶粒位置；对利于马氏体相变的晶粒内部进行加工,得到微米尺寸圆柱样品。样品尺寸减小,马氏体尺寸减小,马氏体难于生成易于逆相变,产生超弹性。同时样品尺寸减小材料强度提高,推迟位错开启时间,减小位错对马氏体逆相变的钉扎作用,进而提高β钛合金超弹性。(The invention discloses a method for improving the superelasticity of a beta titanium alloy, which comprises the following steps: selecting a block beta titanium alloy with a shape memory effect as a sample, and determining a position beneficial to martensitic transformation according to the martensitic transformation strain quantity of the sample; performing electrolytic polishing on the sample; marking the surface of the treated sample; testing and analyzing the processed sample to obtain a grain orientation distribution map of the sample; determining the position of the crystal grain favorable for martensitic transformation according to the position favorable for martensitic transformation by combining the indentation mark and the crystal grain position distribution diagram of the sample; and processing the interior of the crystal grains which are beneficial to martensite phase transformation to obtain a micron-sized cylindrical sample. The sample size is reduced, the size of martensite is reduced, and the martensite is difficult to generate and is easy to reverse phase transformation, so that the superelasticity is generated. Meanwhile, the size of the sample is reduced, the strength of the material is improved, the starting time of dislocation is delayed, the pinning effect of the dislocation on reverse phase transformation of martensite is reduced, and the superelasticity of the beta titanium alloy is improved.)

1. A method of increasing the superelasticity of a beta titanium alloy, comprising the steps of:

step 1, selecting a block beta titanium alloy with a shape memory effect as a sample, and determining a direction beneficial to martensitic transformation according to the martensitic transformation strain quantity of the sample;

step 2, performing electrolytic polishing on the sample;

Step 3, marking the surface of the sample treated in the step 2;

step 4, carrying out test analysis on the sample processed in the step 3 to obtain a grain orientation distribution map of the sample;

Step 5, according to the orientation which is beneficial to martensite phase transformation and obtained in the step 1, determining the position of the crystal grain which is beneficial to martensite phase transformation by combining the mark in the step 3 and the crystal grain orientation distribution diagram of the sample obtained in the step 4;

and 6, processing the interior of the crystal grains beneficial to martensite phase transformation to obtain a micron-sized cylindrical sample.

2. The method for improving the superelasticity of the beta titanium alloy according to claim 1, wherein the step 1 specifically comprises: calculating the phase transformation strain amount generated when the beta phase is transformed to the martensite under different positions, and selecting the position with large phase transformation strain amount as the position beneficial to the martensite transformation.

3. The method for improving the superelasticity of a beta titanium alloy according to claim 1, wherein in the step 3, the surface of the sample is marked by indentation with a hardness tester.

4. The method of claim 1, further comprising compressively deforming the micron-sized cylindrical sample obtained in step 6 to obtain a compressive stress-strain curve and a superelastic deformation.

5. the method for improving the superelasticity of a beta titanium alloy according to claim 1, wherein the test analysis method in step 4 is an EBSD test analysis.

6. the method for improving the superelasticity of a beta titanium alloy according to claim 1, wherein step 6 specifically comprises: and (5) processing the interior of the crystal grains which are beneficial to martensite transformation and obtained in the step 5 by using an FIB technology.

Technical Field

the invention belongs to the technical field of nano material preparation methods, and relates to a method for improving the superelasticity of a beta titanium alloy.

Background

With the development of micro-nano instruments, shape memory alloy can be used as a sensor and an actuating element due to the specific superelasticity of the shape memory alloy, so that the research of people on small-size intelligent metal materials with superelasticity behaviors is stimulated. Compared with the traditional Ti-Ni, Cu-Al-Ni shape memory alloy, the titanium-based shape memory alloy also has excellent obdurability, good corrosion resistance and biocompatibility. The martensite phase transformation is the main load-bearing deformation mode of the super elasticity, and the martensite phase transformation in the titanium alloy mainly occurs in the Beta (Beta) titanium alloy. Under the action of external force, a beta phase matrix can be transformed to an alpha 'phase martensite phase, but the free energy difference between the alpha' martensite and the beta matrix is large, the alpha 'martensite cannot be directly recovered to a parent phase after unloading, and the alpha' martensite is required to be subjected to reverse phase transformation by heating. Thus, there is some shape memory effect in macroscopic bulk beta titanium alloys, but the superelastic behavior is not significant, especially for Ti-Mo and Ti-V based beta titanium alloys, which have superelasticity less than 0.3%.

disclosure of Invention

the invention aims to provide a method for improving the superelasticity of a beta titanium alloy, which can improve the superelasticity of the beta titanium alloy.

The invention adopts the technical scheme that a method for improving the superelasticity of a beta titanium alloy comprises the following steps:

Step 1, selecting a block beta titanium alloy with a shape memory effect as a sample, and determining a direction beneficial to martensitic transformation according to the martensitic transformation strain quantity of the sample;

Step 2, performing electrolytic polishing on the sample;

Step 3, marking the surface of the sample treated in the step 2;

Step 4, carrying out test analysis on the sample processed in the step 3 to obtain a grain orientation distribution map of the sample;

step 5, according to the orientation which is beneficial to martensite phase transformation and obtained in the step 1, determining the position of the crystal grain which is beneficial to martensite phase transformation by combining the mark in the step 3 and the crystal grain orientation distribution diagram of the sample obtained in the step 4;

And 6, processing the interior of the crystal grains which are beneficial to martensite phase transformation to obtain a micron-sized cylindrical sample.

The invention is also characterized in that:

The step 1 specifically comprises the following steps: calculating the phase transformation strain amount generated when the beta phase is transformed to the martensite under different positions, and selecting the position with large phase transformation strain amount as the position beneficial to the martensite transformation.

and 3, carrying out indentation marking on the surface of the sample by adopting a hardness tester.

and (3) carrying out compression deformation on the micrometer-sized cylindrical sample obtained in the step (6) to obtain a compression stress-strain curve and a super-elastic deformation.

The test analysis method in step 4 is EBSD (Electron Backscattered Diffraction) test analysis.

the step 6 specifically comprises the following steps: and (5) processing the interior of the crystal grains which are beneficial to martensite transformation and obtained in the step 5 by using an FIB technology.

the invention has the beneficial effects that: the invention provides a method for improving the superelasticity of a beta titanium alloy, wherein a micron-scale sample is processed by selecting grains favorable for the martensitic phase transformation orientation, the size of the sample is in direct proportion to the size of martensite, and the smaller the size of the martensite is, the harder the martensite is to be generated, but the reverse phase transformation of the martensite is easy to occur. Meanwhile, the sample size is reduced, the material strength is improved, the dislocation starting time is delayed, the pinning effect of the dislocation on the reverse phase transformation of martensite is reduced, and the superelasticity of the beta titanium alloy is obviously improved; in addition, the cylindrical sample is processed, so that the edge angle can be reduced, the dislocation starting is reduced, the reverse phase transformation of martensite is facilitated, and the superelasticity of the alloy is improved.

Drawings

FIG. 1 is a graph of grain orientation distribution EBSD of an embodiment of a method of the present invention for increasing superelasticity of a beta titanium alloy;

FIG. 2 is a drawing of a cylindrical sample of 2 μm diameter machined according to an embodiment of the method of the present invention for increasing superelasticity of a beta titanium alloy;

FIG. 3 is a graph showing the results of a test of a method of improving the superelasticity of a beta titanium alloy according to the present invention.

Detailed Description

the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

A method of increasing the superelasticity of a beta titanium alloy, comprising the steps of:

step 1, selecting a block beta titanium alloy with a shape memory effect as a sample, and determining a direction beneficial to martensitic transformation according to the martensitic transformation strain quantity of the sample;

the method for judging the orientation favorable for martensite transformation comprises the following steps: the transformation of the β phase to the α "martensite generates transformation strains along three main axis directions (x-axis, y-axis, z-axis) of the α" martensite phase, which are η 1, η 2 and η 3, respectively. The deformation along the direction with large phase change strain quantity is beneficial to martensite phase change, and the potential of generating super elasticity is large.

the phase change variables η 1, η 2 and η 3 can be simply calculated by the lattice constants of β and α ″, the crystallographic relationship of the two phases and the following formula:

In the formula:

a ', b ', c ' -the lattice constant of the martensitic phase/m;

a-lattice constant of the beta matrix/m.

Step 2, performing electrolytic polishing on the sample;

step 3, carrying out indentation marking on the surface of the sample treated in the step 2 by adopting a hardness tester;

step 4, testing and analyzing the sample processed in the step 3 by adopting an EBSD technology to obtain a grain orientation distribution map of the sample;

step 5, according to the orientation which is beneficial to martensite phase transformation and obtained in the step 1, determining the position of the crystal grain which is beneficial to martensite phase transformation by combining the indentation mark in the step 3 and the crystal grain orientation distribution diagram of the sample obtained in the step 4;

and 6, processing the interior of the crystal grain which is beneficial to martensite transformation by using an FIB technology to obtain a micron-sized cylindrical sample. The micrometer-sized cylindrical sample had a size of 1 to 10 μm. The cylindrical sample obtained after processing can reduce edges and corners and dislocation starting, and is beneficial to reverse phase transformation of martensite, so that the superelasticity of the beta titanium alloy is improved.

The method also comprises the following testing process: and (3) carrying out compression deformation on the micrometer-sized cylindrical sample after obtaining the micrometer-sized cylindrical sample, and obtaining a compression stress-strain curve and a super-elastic deformation.