阅读说明：本技术 一种近等原子比富镍镍钛合金双程形状记忆效应训练方法 (Near-equal atomic ratio nickel-rich nickel-titanium alloy two-way shape memory effect training method ) 是由 曹姗姗 王丁祥 张新平 马骁 曾才有 赵仲勋 于 2020-05-12 设计创作，主要内容包括：本发明公开了一种近等原子比富镍镍钛合金双程形状记忆效应训练方法。所述的训练方法包括如下步骤：(1)将近等原子比富镍镍钛合金条固溶后进行减薄处理,得到样品条；(2)将步骤(1)所述样品条全部弯曲在半圆柱状约束模具中,将装载样品条的模具进行第一步约束时效处理,温度为450～500℃、时间为1～3h,完毕后立即水淬；然后在相同的模具中进行第二次约束时效处理,温度为250～350℃、时间为10～40h,完毕后立即水淬,即完成训练。本发明训练得到的镍钛双程形状记忆合金材料响应温度区间为40.9～60.2℃,形状回复率提升至96.4％,可广泛应用于工作场合为室温以上的智能器件。(The invention discloses a near-equal atomic ratio nickel-rich nickel-titanium alloy two-way shape memory effect training method. The training method comprises the following steps: (1) carrying out thinning treatment after solid solution on the nickel-rich nickel-titanium alloy strip with the nearly equal atomic ratio to obtain a sample strip; (2) bending all the sample strips in the step (1) in a semi-cylindrical constraint mould, carrying out first-step constraint aging treatment on the mould loaded with the sample strips at the temperature of 450-500 ℃ for 1-3 h, and immediately carrying out water quenching after the first-step constraint aging treatment is finished; and then carrying out secondary constraint aging treatment in the same die at the temperature of 250-350 ℃ for 10-40 h, and immediately carrying out water quenching after the secondary constraint aging treatment is finished, thus finishing the training. The nickel-titanium two-way shape memory alloy material obtained by training has a response temperature range of 40.9-60.2 ℃, the shape recovery rate is improved to 96.4 percent, and the nickel-titanium two-way shape memory alloy material can be widely applied to intelligent devices with the working occasions above room temperature.)

1. A near-equal atomic ratio nickel-rich nickel-titanium alloy two-way shape memory effect training method is characterized by comprising the following steps:

(1) carrying out solid solution treatment on the nickel-rich nickel-titanium alloy strip with nearly equal atomic ratio in a closed inert atmosphere, and carrying out water quenching after the solid solution treatment is finished; performing thickness reduction treatment on the material subjected to water quenching to obtain a sample strip;

(2) bending all the sample strips in the step (1) in a semi-cylindrical constraint mould, carrying out first-step constraint aging treatment on the mould loaded with the sample strips at the temperature of 450-500 ℃ for 1-3 h, and immediately carrying out water quenching after the treatment is finished;

(3) and (3) bending the sample strip subjected to water quenching in the step (2) in the same constraint mould again, carrying out second constraint aging treatment on the mould loaded with the sample strip at the temperature of 250-350 ℃ for 10-40 h, and immediately carrying out water quenching after the second constraint aging treatment, so as to finish the training of the near-equiatomic ratio nickel-rich nickel-titanium alloy two-way shape memory effect.

2. The near-equiatomic ratio nickel-rich nickel-titanium alloy two-way shape memory effect training method as claimed in claim 1, wherein the thickness of the sample strip in the step (1) is measured by a vernier caliper, the thickness of the sample strip is recorded as t, and the thickness is calculated according to a formulaIs calculated to obtain wherein_maxIs the maximum strain value of the sample strip, 0 <_maxLess than or equal to 2 percent; and R is the curvature radius of the arc-shaped groove of the semi-cylindrical constraint mould in the step (2).

3. The near-equiatomic ratio nickel-rich nickel-titanium alloy two-way shape memory effect training method according to claim 1 or 2, wherein in the near-equiatomic ratio nickel-rich nickel-titanium alloy strip of step (1), the ratio of nickel atoms: the number ratio of titanium atoms is 50.8-51: 49.2-49.

4. The near-equiatomic ratio nickel-rich nickel-titanium alloy two-way shape memory effect training method according to claim 3, wherein in the near-equiatomic ratio nickel-rich nickel-titanium alloy strip of step (1), the ratio of nickel atoms: the number ratio of titanium atoms was 51:49.

5. The near-equiatomic ratio nickel-rich nickel-titanium alloy two-way shape memory effect training method according to claim 1 or 2, characterized in that the temperature of the solution treatment in the step (1) is 800-950 ℃, and the time of the solution treatment is 1-10 h.

6. The near-equiatomic ratio nickel-rich nickel-titanium alloy two-way shape memory effect training method as claimed in claim 3, wherein the thickness of the sample strip in step (1) is 0.5-0.7 mm; the curvature radius of an arc-shaped groove of the semi-cylindrical constraint mould in the step (2) is 15-35 mm; and (2) the inert atmosphere in the step (1) is argon.

7. The near-equiatomic ratio nickel-rich nickel-titanium alloy two-way shape memory effect training method according to claim 1, wherein the near-equiatomic ratio nickel-rich nickel-titanium alloy strip in the step (1) is prepared by a rapid solidification process.

8. The near-equiatomic ratio nickel-rich nickel-titanium alloy two-way shape memory effect training method as claimed in claim 7, wherein the rapid solidification process in step (1) is performed by: after vacuum arc melting, suction casting the molten alloy into a water-cooled oxygen-free copper mold; the corresponding dimension of the alloy strip is 50-100 mm multiplied by 8-10 mm multiplied by 0.5-1.5 mm.

9. The near-equiatomic ratio nickel-rich nickel-titanium alloy two-way shape memory effect training method according to claim 1, wherein the thinning treatment in step (1) uses a stainless steel mold, which is ensured to have a flat surface and to have good contact with the surface of the sample during adhesion, and the sample cannot tilt during thinning, so as to ensure that the thickness of the middle part of the sample meets the design requirement.

10. The training method for the near-equiatomic ratio nickel-rich nickel-titanium alloy two-way shape memory effect according to claim 1, wherein the installation orientation of the sample strip in the constraining mold in the step (3) is consistent with the installation orientation of the sample strip in the semi-cylindrical constraining mold in the step (2) so as to keep the tensile and compressive stress side of the sample strip unchanged.

Technical Field

The invention belongs to the field of heat treatment processes, and particularly relates to a near-equal atomic ratio nickel-rich nickel-titanium alloy two-way shape memory effect training method.

Background

The nickel-titanium alloy as a typical functional material has shape memory effect and superelasticity, has excellent biocompatibility, wear resistance, corrosion resistance and high damping property, and is widely applied to the fields of daily life, aerospace, biomedical treatment, mechanical engineering and the like. The material can spontaneously generate deformation during temperature rise and fall by utilizing the two-way shape memory effect, and further can be used as various drivers, actuators, sensors and the like, and has important application value. This property must be achieved through process "training" approaches, which typically include once-through excessive deformation of martensite, thermal cycling, and constrained aging. Wherein the matrix produces a relatively stable coherent precipitated phase N due to the efficiency of confinement_i4Ti₃Therefore, a stable coherent stress field is introduced into the matrix to influence the thermo-elastic martensite phase transformation of the material, so that the nickel-titanium alloy strip with remarkable two-way shape memory effect and high fatigue stability can be prepared.

The traditional constrained aging process is to constrain Ni-rich nickel-titanium alloy strips or alloy wires into a ring shape by using a mold, then heat the mold and a sample to a certain temperature, usually 300-550 ℃, then keep the temperature for a period of time at the temperature, and immediately quench the material after the temperature is finished, so that the material keeps the tissue form at a high temperature. We generally refer to this aging approach as primary constraint aging. Although good two-way shape memory recovery can be obtained by the aging process, the aging process needs to be carried out at a higher temperature for about 100 hours, and is a relatively time-consuming and energy-consuming process. In addition, higher temperature aging results in lower equilibrium R transition temperatures for the samples, typically below room temperature. This results in the sample not being able to actively deform with temperature above room temperature, i.e. the service conditions become severe.

In view of the situation that the current constrained aging process is time-consuming and energy-consuming and inefficient, and cannot process nickel-titanium alloy which can reach ideal service conditions, an efficient aging process is urgently to be invented to solve the problems.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide a near-equal atomic ratio nickel-rich nickel-titanium alloy two-way shape memory effect training method.

The invention adopts a two-step constraint aging process, greatly improves the efficiency of heat treatment, shortens the aging time and saves the energy consumption while effectively improving the two-way shape memory effect of a sample, and in addition, the process provided by the invention can improve the R phase transition temperature of the nickel-titanium alloy, optimizes the material performance, and can be widely applied to intelligent devices with the working occasion of more than room temperature, especially the field of biological medical treatment.

The purpose of the invention is realized by the following technical scheme:

a near-equal atomic ratio nickel-rich nickel-titanium alloy two-way shape memory effect training method comprises the following steps:

(1) carrying out solid solution treatment on the nickel-rich nickel-titanium alloy strip with nearly equal atomic ratio in a closed inert atmosphere, and carrying out water quenching after the solid solution treatment is finished; performing thickness reduction treatment on the material subjected to water quenching to obtain a sample strip;

(2) bending all the sample strips in the step (1) in a semi-cylindrical constraint mould, enabling the materials to be deformed into an arc shape with corresponding curvature under the constraint action of the mould, carrying out first-step constraint aging treatment on the mould loaded with the sample strips at the temperature of 450-500 ℃ for 1-3 h, and immediately carrying out water quenching after the first-step constraint aging treatment is finished;

(3) and (3) bending the sample strip subjected to water quenching in the step (2) in the same constraint mould again, carrying out second constraint aging treatment on the mould loaded with the sample strip at the temperature of 250-350 ℃ for 10-40 h, and immediately carrying out water quenching after the second constraint aging treatment, so as to finish the training of the near-equiatomic ratio nickel-rich nickel-titanium alloy two-way shape memory effect.

Preferably, the inert atmosphere in step (1) is argon.

Preferably, the temperature of the solution treatment in the step (1) is 800-950 ℃, and the time of the solution treatment is 1-10 h.

Preferably, the thickness of the sample strip in the step (1) is measured by a vernier caliper, and the thickness of the sample strip is recorded as t according to the formulaIs calculated to obtain wherein_maxIs the maximum strain value of the sample strip, 0 <_maxLess than or equal to 2 percent; and R is the curvature radius of the arc-shaped groove of the semi-cylindrical constraint mould in the step (2).

Preferably, the thickness of the sample strip in the step (1) is 0.5-0.7 mm; and (3) the curvature radius of the arc-shaped groove of the semi-cylindrical constraint mould in the step (2) is 15-35 mm.

Preferably, the near-equiatomic ratio nickel-rich nickel-titanium alloy strip in the step (1) is prepared by a rapid solidification process.

Preferably, the rapid solidification process in step (1) is performed in the following manner: after vacuum arc melting, suction casting the molten alloy into a water-cooled oxygen-free copper mold; the corresponding dimension of the alloy strip is 50-100 mm (length) multiplied by 8-10 mm (width) multiplied by 0.5-1.5 mm (thickness).

Preferably, the atomic ratio of nickel atoms in the nickel-rich nickel-titanium alloy strip in the step (1) is approximately equal to the atomic ratio of nickel atoms: the number ratio of titanium atoms is 50.8-51: 49.2-49.

Preferably, the stainless steel die is used for thinning treatment in the step (1), the surface of the die is smooth and is in good contact with the surface of the sample during adhesion, the sample cannot incline in the thinning process, and the thickness of the middle part of the sample is ensured to meet the design requirement.

Preferably, the semi-cylindrical constraint mould in the step (2) is in a mould with multiple cavities, and the mould is positioned and locked by using screws; more preferably 3 arc-shaped recesses, the mould being positioned and locked using 4 screws.

Preferably, the installation orientation of the sample strip in the constraining mold in the step (3) is consistent with the installation orientation of the sample strip in the semi-cylindrical constraining mold in the step (2), so that the tensile and compressive stress side of the sample strip is kept unchanged.

The principle of the invention is as follows:

the study shows that Ni₄Ti₃The nucleation and growth process of the precipitated phase is controlled by diffusion type phase change, the nucleation stage is mainly controlled by short-range diffusion of Ni atoms, and the growth process is determined by the long-range diffusion of the Ni atoms. The first step of the two-step ageing is selected at a higher temperature, the purpose of which is to increase the diffusion rate of the Ni atom concentration in the B2 matrix, so that the precipitate phase grows rapidly in a short time. The grown precipitated phases form preferred orientation arrangement in a matrix, and then stable directional coherent stress field is introduced to dominate the variant selection of phase change behavior, so that a normal two-way shape memory effect is formed macroscopically. In addition, the grown precipitated phase also provides an acceptor for subsequent Ni atom diffusion, and the precipitated phase continuously grows, so that the coherent stress field is further increased. The second step of aging adopts low-temperature aging, so that the nucleation rate can be greatly improved. More importantly, the supersaturation degree of Ni atoms in the B2 matrix is increased, so that the diffusion of the Ni atoms in the matrix has two points, and the short-distance diffusion can form new Ni₄Ti₃The separated phase core and the long-range diffusion will enter into the first step of the grown Ni₄Ti₃The inside of the precipitated phase is fully grown, so that the coherent stress field in the matrix is maximized, and the shape memory recovery rate is improved. The low temperature aging of the second step will also result in a reduction in the equilibrium Ni atom concentration of the matrix, thus increasing the R transformation temperature and hence the response temperature of the alloy strip.

The application of the constrained aging shape memory effect training process in the NiTi alloy is still in the initial stage of exploration, two-step constrained aging is not proposed at present, the technical difficulty is to reasonably control the selection of the temperature and time of the two-step aging, for example, the first-step aging temperature is too high, so that Ni can be generated₄Ti₃The precipitated phase is rapidly segregated, and the second step aging time is too short to allow the precipitated phase to grow sufficiently. In other words, Ni needs to be selected and matched through reasonable parameters₄Ti₃The final morphology of the precipitated phase reaches the optimum size, and the two-way shape memory effect can only be optimized.

Compared with the prior art, the invention has the following advantages:

(1) training efficiency has been promoted to the high efficiency. The two-step constraint aging process provided by the invention can effectively shorten the aging time, reduce the aging temperature and reduce the energy consumption from two aspects of time and temperature; in addition, the invention innovatively provides a one-mold multi-cavity constraint mold design, so that the training efficiency is increased in a multiple mode from the aspect of yield.

(2) The training mode is simple, and the training effect is obvious. According to the invention, through a two-step constraint aging training process, the nickel-titanium alloy has a two-way shape memory effect superior to that of a sample in the traditional process, namely, the recovery rate is higher (up to 96.4%); meanwhile, the training mode is simple, and the method is particularly suitable for mass production in engineering application.

(3) The product performance is effectively improved. The invention not only improves the two-way shape memory recovery rate of the nickel-titanium sample strip, but also obviously improves the R phase transition temperature of the material, namely the temperature corresponding to the deformation generated during the temperature reduction is improved, so that the material meets the loose service condition, and can be widely applied to intelligent devices with the temperature above room temperature in a working occasion.

Drawings

FIG. 1 is a schematic view of a multi-cavity confinement mold and a sample strip holding state of the present invention, wherein the top view is a front view and the bottom view is a top view (the top view is a state without a semicircular ring holding sleeve); 1-semicircular ring fixing sleeve, 2-inner hexagonal fixing screw, 3-arc groove, 4-screw blind hole and 5-semicircular column base with groove.

FIG. 2 is a graph of a constrained aging process of example 1 of the present invention.

FIG. 3 shows Ni after two-step aging in example 1₅₁Ti₄₉DSC curve of the alloy bars.

FIG. 4 shows Ni after the two-step aging treatment in example 1₅₁Ti₄₉And (3) bright field image of the alloy strip by a transmission electron microscope.

Detailed Description

The present invention will be further described with reference to the following specific examples and drawings, but the present invention is not limited to these examples.