阅读说明：本技术 一种高Ni纳米晶NiTi形状记忆合金型材及其制备方法 (high-Ni nanocrystalline NiTi shape memory alloy profile and preparation method thereof ) 是由 郝世杰 黄诗涵 孙震 崔立山 田昀 黎昱 于 2020-06-10 设计创作，主要内容包括：本发明提供了一种高Ni纳米晶NiTi形状记忆合金型材及其制备方法。在该型材中,高Ni纳米晶NiTi形状记忆合金的化学式为Ni<Sub>a</Sub>Ti<Sub>100-a</Sub>,51.2≤a≤55。本发明提供的上述型材的制备方法包括如下步骤：使Ni、Ti原材料依次经过熔炼、均匀化退火、热锻成型、塑性加工处理,制得型材初坯；对所述型材初坯进行高温固溶处理、低温时效处理、冷变形处理、晶化退火处理,得到所述高Ni纳米晶NiTi形状记忆合金型材。本发明的高Ni纳米晶NiTi记忆合金型材中存在晶界富Ni而晶内贫Ni的成分非均匀现象。此外,该高Ni纳米晶NiTi记忆合金型材能够在-190℃至120℃的温度范围内具有良好的超弹特性。(The invention provides a high-Ni nanocrystalline NiTi shape memory alloy section and a preparation method thereof. In the section bar, the chemical formula of the high Ni nanocrystalline NiTi shape memory alloy is Ni a Ti 100‑a And a is more than or equal to 51.2 and less than or equal to 55. The preparation method of the profile provided by the invention comprises the following steps: sequentially carrying out smelting, homogenizing annealing, hot forging forming and plastic processing on Ni and Ti raw materials to obtain a profile blank; and carrying out high-temperature solid solution treatment, low-temperature aging treatment, cold deformation treatment and crystallization annealing treatment on the profile primary blank to obtain the high-Ni nanocrystalline NiTi shape memory alloy profile. The high Ni nanocrystalline NiTi memory alloy section bar of the invention has the crystal boundary rich Ni and the crystal interior poor NiThe composition of (2) is non-uniform. In addition, the high Ni nanocrystalline NiTi memory alloy section bar can have good super-elastic characteristics in the temperature range of-190 ℃ to 120 ℃.)

1. A high Ni nanocrystalline NiTi shape memory alloy section bar, wherein, the chemical formula of the high Ni nanocrystalline NiTi shape memory alloy is Ni_aTi_100-a，51.2≤a≤55。

2. The high Ni nanocrystalline NiTi shape memory alloy profile of claim 1, wherein the high Ni nanocrystalline NiTi shape memory alloy consists of uniform NiTi nanocrystals.

3. The high Ni nanocrystalline NiTi shape memory alloy profile of claim 2, wherein the nanocrystalline grains have an average diameter of 5-50 nm.

4. The high Ni nanocrystalline NiTi shape memory alloy profile of claim 2 or 3, wherein grain boundaries of the nanocrystals are Ni-rich and Ni-poor intragranular.

5. The high Ni nanocrystalline NiTi shape memory alloy profile of any one of claims 1-4, wherein the profile is a wire, a plate or a bar.

6. The method for preparing a high Ni nanocrystalline NiTi shape memory alloy profile as claimed in any one of claims 1 to 5, which comprises the steps of:

sequentially carrying out smelting, homogenizing annealing, hot forging forming and plastic processing on Ni and Ti raw materials to obtain a profile blank;

and carrying out high-temperature solid solution treatment, low-temperature aging treatment, cold deformation treatment and crystallization annealing treatment on the profile primary blank to obtain the high-Ni nanocrystalline NiTi shape memory alloy profile.

7. The preparation method according to claim 6, wherein the temperature of the high-temperature solution treatment is 750-1200 ℃, and the holding time is 10 minutes-10 hours; preferably, the temperature of the high-temperature solution treatment is 800-1000 ℃, and the heat preservation time is 10-30 minutes.

8. The preparation method according to claim 6 or 7, wherein the temperature of the low-temperature aging treatment is 300-700 ℃, and the holding time is 1 minute-10 hours; preferably, the temperature of the low-temperature aging treatment is 450-550 ℃, and the heat preservation time is 5-20 minutes.

9. The production method according to any one of claims 6 to 8, wherein the cold deformation treatment has a deformation amount of 40% to 200%.

10. The production method according to any one of claims 6 to 9, wherein the temperature of the crystallization annealing treatment is 300 ℃ to 600 ℃, and the treatment time is 1 minute to 5 hours; preferably, the temperature of the crystallization annealing treatment is 350-450 ℃, and the treatment time is 5-20 minutes.

Technical Field

The invention relates to the technical field of metal nano materials, in particular to a preparation method of a high-Ni nanocrystalline NiTi shape memory alloy profile.

Background

The NiTi shape memory alloy is widely applied to the fields of biological medicine, aerospace, automobiles and the like. Especially for deep space (moon, Mars, etc.) detectors, the special requirements for the weight reduction and the service temperature of materials require that the NiTi shape memory alloy has high superelastic stress in a wide temperature range. NiTi shape memory alloys have been reported to fail to meet the above requirements. As is well known, for the super elastic NiTi memory alloy, the content of Ni is increased to quickly reduce A_f(Ni atom content increases by 0.1 mol% per A)_f10 ℃ reduction), and the stable existence temperature range of austenite is remarkably widened. Meanwhile, the stress-induced martensite phase transformation can be prevented by increasing the content of solid-solution Ni atoms, and the superelastic stress is obviously increased. It can be guessed that the NiTi memory alloy (such as Ni) with high Ni content₅₂Ti₄₈at.%) is expected to achieve high superelastic stress over a wide temperature range. Disappointingly, the high Ni-NiTi memory alloys prepared by the conventional method (high temperature solution + quenching) exhibit tensile brittle fracture over a wide temperature range and fail to exhibit tensile superelastic properties. It is speculated that the superelastic properties could be exhibited if the rupture strength of the high Ni-NiTi memory alloy could be increased so that the rupture strength is higher than the superelastic stress. Among them, fine grain strengthening is an effective method for improving the fracture strength.

Research shows that the reported nanocrystalline NiTi memory alloy has ultrahigh yield strength or fracture strength compared with the coarse-crystal NiTi memory alloy. However, the existing preparation of nanocrystalline NiTi shape memory alloys is obtained by large plastic deformation and subsequent low temperature crystallization annealing. For Ni-NiTi memory alloy with high solid solution state, when the atomic percentage of Ni is more than 51%, the plasticity of the alloy is poor, and large plastic deformation processing cannot be carried out, so that nano crystallization cannot be realized by large plastic deformation and a subsequent low-temperature crystallization annealing method. Therefore, how to prepare the high Ni nanocrystalline NiTi shape memory alloy is a problem which is urgently needed to be solved at present.

Disclosure of Invention

Aiming at the problems in the prior art, the invention aims to provide a high-Ni nanocrystalline NiTi shape memory alloy profile and a preparation method thereof.

In order to achieve the above purpose, the invention provides a high Ni nanocrystalline NiTi shape memory alloy section, wherein the chemical formula of the high Ni nanocrystalline NiTi shape memory alloy is Ni_aTi_100-aAnd a is more than or equal to 51.2 and less than or equal to 55. Namely, in the high Ni nanocrystalline NiTi shape memory alloy, the atomic percent content of Ni is a percent, and the atomic percent content of Ti is (100-a)%.

According to a specific embodiment of the present invention, preferably, the high Ni nanocrystalline NiTi shape memory alloy described above consists of uniform NiTi nanocrystals. The average diameter of the crystal grains of the nanocrystals is preferably 5 to 50nm, for example 10 nm.

According to a specific embodiment of the present invention, preferably, in the high Ni nanocrystalline NiTi shape memory alloy profile, the grain boundaries of the nanocrystals are Ni-rich and Ni-poor within the crystal, with distinct compositional non-uniformity characteristics.

According to a particular embodiment of the invention, the profile may be a wire, a plate or a bar or the like.

The invention also provides a preparation method of the high Ni nanocrystalline NiTi shape memory alloy section, which comprises the following steps:

sequentially carrying out smelting, homogenizing annealing, hot forging forming and plastic processing on Ni and Ti raw materials to obtain a profile blank;

and carrying out high-temperature solid solution treatment, low-temperature aging treatment, cold deformation treatment and crystallization annealing treatment on the profile primary blank to obtain the high-Ni nanocrystalline NiTi shape memory alloy profile.

In the preparation method, preferably, the temperature of the high-temperature solution treatment is 750-1200 ℃, and the heat preservation time is 10 minutes-10 hours; more preferably, the temperature of the high-temperature solution treatment is 800-1000 ℃, and the heat preservation time is 10-30 minutes.

In the preparation method, preferably, the temperature of the low-temperature aging treatment is 300-700 ℃, and the heat preservation time is 1 minute-10 hours; preferably, the temperature of the low-temperature aging treatment is 450-550 ℃, and the heat preservation time is 5-20 minutes.

In the above production method, preferably, the cold deformation amount is 40% to 200%.

In the above preparation method, preferably, the temperature of the crystallization annealing treatment is 300 ℃ to 600 ℃, and the treatment time is 1 minute to 5 hours; preferably, the temperature of the crystallization annealing treatment is 350-450 ℃, and the treatment time is 5-20 minutes.

According to a specific embodiment of the present invention, the above preparation method can be performed according to the following specific steps:

1) is represented by the chemical formula Ni_aTi_100-aA is not less than 51.2 and not more than 55, and Ni and Ti are respectively weighed as raw materials;

2) placing the raw material in a vacuum degree higher than 10^-1Smelting in a smelting furnace under the protection of Pa or inert gas, and then casting to obtain a NiTi binary alloy ingot;

3) homogenizing the cast ingot at the temperature of 900 ℃ and 1000 ℃ in a vacuum environment for 5-50 hours, and cooling;

4) carrying out hot forging molding on the ingot subjected to the homogenization treatment at the temperature of 700-900 ℃;

5) carrying out plastic processing treatment on the NiTi alloy material subjected to hot forging forming to obtain a corresponding profile primary blank;

6) carrying out high-temperature solution treatment on the obtained profile primary blank, wherein the treatment temperature is 750-1200 ℃, the heat preservation time is 10 minutes-10 hours, and the cooling mode can be water quenching or air cooling;

7) carrying out low-temperature aging treatment on the primary blank of the solid-solution-state section, wherein the treatment temperature is 300-700 ℃, the heat preservation time is 1 minute-10 hours, and the cooling mode can be water quenching or air cooling;

8) carrying out large cold deformation treatment on the primary blank of the section subjected to low-temperature aging treatment, wherein the cold deformation is 40-200%;

9) and (3) carrying out crystallization annealing treatment on the section bar primary blank after the large cold deformation treatment, wherein the treatment temperature is 300-600 ℃, and the treatment time is 1 minute-5 hours, so as to obtain the high-Ni nanocrystalline NiTi shape memory alloy section bar.

The invention adopts a mode of high-temperature solid solution and low-temperature aging, can obviously improve the plasticity of the high Ni-NiTi memory alloy with the Ni atom percentage more than 51 percent, allows subsequent large cold deformation processing, and obtains the effect completely different from the prior art, in the prior art, the aging treatment can improve the strength but reduce the plasticity of the NiTi memory alloy with the Ni atom percentage less than 51 percent. And then, carrying out low-temperature crystallization annealing treatment on the amorphous high Ni-NiTi alloy obtained by large cold deformation processing to prepare the high Ni nanocrystalline NiTi shape memory alloy section.

The high Ni nanocrystalline NiTi memory alloy section bar has the phenomenon of nonuniform components with Ni-rich crystal boundary and Ni-poor crystal interior. In addition, the high Ni nanocrystalline NiTi memory alloy section bar can have good super-elastic characteristics in the temperature range of-190 ℃ to 120 ℃.

Drawings

FIG. 1 is a transmission electron microscopy brightfield image of a longitudinal section of a wire subjected to high-temperature solution treatment at 900 ℃ for 10 minutes, provided in example 1 of the present invention.

FIG. 2 is a transmission electron micrograph of a longitudinal section of a wire rod aged at 500 ℃ for 1 hour according to example 1 of the present invention.

FIG. 3 is a transmission electron micrograph of a longitudinal section of a wire subjected to 71% cold drawing deformation according to example 1 of the present invention.

FIG. 4 is a DSC curve of 71% cold-drawn deformed wire provided in example 1 of the present invention.

FIG. 5 is a bright field transmission electron micrograph of a longitudinal section of a wire treated at 390 ℃ for 10 minutes according to example 1 of the present invention.

FIG. 6 shows the three-dimensional atom probe result of the NiTi shape memory alloy with high Ni nano-crystals provided in example 1 of the present invention.

FIG. 7 is a tensile stress-strain curve of the NiTi shape memory alloy with high Ni content and nano-crystalline at different temperatures, which is provided in example 1 of the present invention.

Detailed Description

The technical solutions of the present invention will be described in detail below in order to clearly understand the technical features, objects, and advantages of the present invention, but the present invention is not limited to the practical scope of the present invention.