CN110923508A - NiTiHfSc high-temperature shape memory alloy and preparation method thereof - Google Patents

Abstract

The invention provides a NiTiHfSc high-temperature shape memory alloy and a preparation method thereof. Firstly, weighing Ti, Ni, Hf and Sc; secondly, smelting the raw materials into ingots in a non-consumable vacuum arc furnace; thirdly, placing the cast ingot into a vacuum furnace for homogenization treatment; fourthly, carrying out solid solution treatment on the cast ingot in a vacuum furnace to obtain Ti with a chemical formula_{x‑ a}Ni_yHf_zSc_aThe high temperature shape memory alloy of (1), wherein x + y + z is 100, y is 50 to 51, z is 15 to 25, a is 0 to 1.5, and the rest is x. The invention solves the problems of poor processing performance, low shape recovery rate and poor phase change thermal cycle stability of the existing TiNiHf alloy. The invention has simple process, higher phase-change temperature of the obtained product, good phase-change thermal cycle stability and good shape memory effect, and is a shape memory alloy with application prospect. The method is used for preparing the shape memory alloy.

Description

NiTiHfSc high-temperature shape memory alloy and preparation method thereof

Technical Field

The invention relates to a shape memory alloy, in particular to a high-temperature shape memory alloy. The invention also relates to a preparation method of the shape memory alloy.

Background

The shape memory alloy is a metal intelligent material integrating sensing and driving. The martensite phase transition temperature of the traditional shape memory alloy, such as TiNi binary alloy, is lower than 100 ℃, and the requirement of high-temperature occasions, such as fire alarms, automobiles, nuclear reactors and the like, can not be met. Heretofore, the TiNi-based high-temperature shape memory alloy mainly includes ti (nix) (X ═ Pd, Pt, Au) alloy and ni (tix) (X ═ Hf, Zr) alloy. The ti (nix) (X ═ Pd, Pt, Au) alloy contains a large amount of noble metal elements, which results in an expensive alloy and failure to achieve practical engineering applications. Zr is less effective than Hf in increasing the martensitic transformation temperature of the alloy, and the shape recovery characteristics of the NiTiZr alloy are inferior to that of the NiTiHf alloy. Therefore, the NiTiHf alloy is a high-temperature shape memory alloy with great development prospect. However, the thermal cycle stability of the martensitic transformation of the NiTiHf high-temperature shape memory alloy is poor, for example, the martensitic transformation temperature of the NiTiHf alloy is reduced by 14-25 ℃ after 10 thermal cycles. In addition, the low critical slip stress of NiTiHf high temperature shape memory alloys results in poor shape recovery characteristics of the alloys. NiTiHf high-temperature shape memory alloy is high in brittleness, so that the critical sliding stress of the alloy is difficult to improve in a plastic processing mode. Aging can also increase the critical slip stress of the alloy, but is only applicable to Ni-rich NiTiHf alloys. The Ni-rich NiTiHf alloy still has poor workability. Alloying is another effective means for improving the critical sliding stress of the NiTiHf high-temperature shape memory alloy. For example, Pd is added into NiTiHf alloy to raise the yield strength of the alloy. However, Pd is expensive. The poor shape recovery characteristics of NiTiHf alloy greatly restrict the practical engineering application of the alloy. Therefore, the need for other alloy elements to prepare the high temperature shape memory alloy with high strength, high shape recovery and excellent cold and hot processing ability is still needed.

Disclosure of Invention

The invention aims to provide the NiTiHfSc high-temperature shape memory alloy with good phase change thermal cycling stability and high shape recovery rate. The invention also aims to provide a preparation method of the NiTiHfSc high-temperature shape memory alloy.

The purpose of the invention is realized as follows:

the chemical formula of the NiTiHfSc high-temperature shape memory alloy is Ti_x-aNi_yHf_zSc_aWherein x + y + z is 100, y is 50-51, z is 15-25, a is 0-1.5, and the rest is x.

The preparation method of the NiTiHfSc high-temperature shape memory alloy comprises the following steps:

step one, according to the mass ratio of Ti: ni: hf: weighing Ti, Ni, Hf and Sc according to the proportion of y to z to a, wherein x + y + z is 100, y is 50-51, z is 15-25, and a is 0-1.5;

step two, putting the raw materials weighed in the step one into a non-consumable vacuum arc furnace, and vacuumizing to ensure that the vacuum degree of the back bottom reaches 2 multiplied by 10^-2～2×10^-3Pa, then introducing high-purity argon to the pressure in the furnace of 300-500Pa, smelting the raw materials into a button-shaped ingot by using a high-temperature electric arc, then overturning, and repeatedly smelting for 6-8 times;

step three, putting the button-shaped cast ingot obtained in the step two into a vacuum furnace, and vacuumizing to ensure that the vacuum degree reaches 4 multiplied by 10^-2Pa, keeping the temperature at 900-1100 ℃ for 3h to obtain Ti_x-aNi_yHf_zSc_aHigh temperature shape memory alloys.

The invention solves the problems of poor martensite phase transformation thermal cycle stability and poor shape recovery characteristic of the NiTiHf high-temperature shape memory alloy, and high cost or narrow application range of the existing means.

Generally, the addition of Sc to NiTi-based alloys will lower the martensitic transformation temperature. According to the invention, the contents of the NiTiHf alloy component and the Sc element are adjusted, so that the addition of the Sc element can improve the martensitic transformation temperature of the NiTiHf alloy, and the NiTiHf alloy can still be used as a high-temperature shape memory alloy. In addition, Sc element has large chemical activity, and part of Sc element reacts with residual oxygen in the vacuum furnace during smelting to form fine Sc₂O₃The particles can achieve the effect of strengthening the second phase. Meanwhile, part of Sc element is dissolved in the matrix to play a role in solid solution strengthening. Therefore, the Sc element is added into the NiTiHf alloy, and the critical slip stress of the alloy can be improved without reducing the phase transition temperature of the alloy, so that the aim of improving the shape recovery characteristic of the alloy is fulfilled. More importantly, the Sc element can greatly improve the NiTiHf alloy martensite phase transformationThermal cycling stability of (a). The preparation method is simple, and the prepared alloy has good phase-change thermal cycle stability and high shape recovery rate, and is a novel high-temperature shape memory alloy with application prospect.

The method is used for preparing the NiTiHfSc high-temperature shape memory alloy.

Drawings

FIG. 1 is Ti prepared in example one_28.7Ni_50.3Hf₁₅Sc₁Back-scattered electron images of the alloy;

FIG. 2 is Ti prepared in example one_28.7Ni_50.3Hf₁₅Sc₁A DSC curve of the alloy;

FIG. 3 is Ti prepared in example one_28.7Ni_50.3Hf₁₅Sc₁Change of martensite phase transformation after 10 times of alloy thermal cycle

FIGS. 4 a-4 c are Ti prepared in example one_28.7Ni_50.3Hf₁₅Sc₁Image of alloy one-way shape memory effect.

Detailed Description

The chemical formula of the TiNiHfSc shape memory alloy is Ti_x-aNi_yHf_zSc_aWherein x + y + z is 100, y is 50-51, z is 15-25, a is 0-1.5, and the rest is x.

Ti of the invention_x-aNi_yHf_zSc_aThe preparation method of the shape memory alloy comprises the following steps:

weighing Ti, Ni, Hf and Sc according to the mass ratio of (x-a) y: z: a, wherein x + y + z is 100, y is 50-51, z is 15-25, a is 0-1.5, and the balance is x;

secondly, putting the Ni, Ti, Hf and Sc weighed in the step one into a non-consumable vacuum arc furnace, vacuumizing to enable the degree of vacuum of the back bottom to reach 2 x 10^-2～2×10^-3Pa, then introducing high-purity argon until the pressure in the furnace is 300Pa, smelting raw materials of Ni, Ti, Hf and Sc into an ingot by using high-temperature electric arc, then overturning, and repeatedly smelting for 6-8 times;

thirdly, putting the cast ingot obtained in the second step into a vacuum furnace, and pumpingVacuum to make vacuum degree reach 4X 10^-2Pa, keeping the temperature at 960-1200 ℃ for 6-8 h;

fourthly, carrying out hot extrusion on the ingot casting processed in the third step at 850-950 ℃ to obtain a bar material with the diameter of about 2-3 cm, putting the bar material into a vacuum furnace, vacuumizing to enable the vacuum degree to reach 2 x 10^-2Keeping the temperature of the mixture Pa at 800-1000 ℃ for 1-2 h to obtain Ti_x-aNi_yHf_zSc_aHigh temperature shape memory alloys.

The purity of Ni, Ti, Hf and Sc in the first step is not lower than 99.9%.

Ti obtained by the above method_28.7Ni_50.3Hf₁₅Sc₁The high-temperature shape memory alloy has good thermal cycle stability and shape memory effect, and the martensite phase transformation starting temperature is about 217.37 ℃; can completely meet the application requirement of the high-temperature shape memory alloy.

The invention is described in more detail below by way of example.

The first embodiment is as follows:

this example is a Ti_28.7Ni_50.3Hf₁₅Sc₁The preparation method of the shape memory alloy comprises the following steps:

firstly, according to the mass ratio of 28.7: 50.3: 15: 1, weighing Ni, Ti, Hf and Sc with the purity of 99.9 percent;

secondly, putting the Ni, Ti, Hf and Sc weighed in the step one into a non-consumable vacuum arc furnace, vacuumizing to enable the degree of vacuum of the back bottom to reach 2 x 10^-3Pa, then filling high-purity argon with the purity of 99.9 percent until the pressure in the furnace is 300Pa, and smelting the raw materials of Ni, Ti, Hf and Sc into cast ingots by utilizing high-temperature electric arcs;

thirdly, putting the button-shaped cast ingot obtained in the second step into a vacuum furnace, and vacuumizing to ensure that the vacuum degree reaches 2 multiplied by 10^-2Pa, keeping the temperature at 980 ℃ for 8h for homogenization treatment to obtain Ti_28.7Ni_50.3Hf₁₅Sc₁A high temperature shape memory alloy;

ti prepared from example one by spark erosion cutting_28.7Ni_50.3Hf₁₅Sc₁Cutting a cuboid with a length of 20mm, a width of 20mm and a thickness of 1.3mm from the high-temperature shape memory alloy, grinding the cut trace on the surface with sand paper, polishing to obtain a backscattered electron image, and observing the sample, wherein FIG. 1 is the backscattered electron image of the sample, wherein the white contrast phase is Hf-rich phase, and the black contrast phase is Sc₂O₃The gray contrast phase is the matrix.

Ti prepared from example one by spark erosion cutting_28.7Ni_50.3Hf₁₅Sc₁A rectangular parallelepiped of 3mm in length, 1.5mm in width and about 30mg in weight was cut out of the high temperature shape memory alloy, the surface of the cut was polished with sandpaper, and the phase change behavior was measured on a Perkin-Elmer Diamond DSC, and FIG. 2 is a DSC curve of the sample showing the martensite phase transition onset temperature (M)_s) The temperature was 217.37 ℃. It can be seen that the phase transition temperature is higher than Ti_29.7Ni_50.3Hf₁₅High temperature shape memory alloy (163.73 deg.C). FIG. 3 shows a sample of Ti_28.7Ni_50.3Hf₁₅Sc₁The martensite phase transformation temperature of the alloy is reduced by 8.15 ℃ in 10 times of thermal cycles after the alloy is subjected to the martensite phase transformation change for 10 times of thermal cycles. The martensite phase transformation thermal cycle stability of the visible sample is superior to that of Ti_29.7Ni_50.3Hf₁₅And (3) alloying.

Ti prepared from example one by spark erosion cutting_28.7Ni_50.3Hf₁₅Sc₁Cutting 35mm long strip of 0.5mm thickness from the high temperature shape memory alloy, grinding surface cutting trace with sand paper, bending the strip by bending mold with 6% deformation, and heating to 350 deg.C. FIGS. 4 a-4 c are prepared Ti_28.7Ni_50.3Hf₁₅Sc₁The one-way shape memory effect picture of the alloy is heated and then the deformation is completely recovered.

Claims (2)

1. A NiTiHfSc high-temperature shape memory alloy is characterized in that: has a chemical formula of Ti_x-aNi_yHf_zSc_aWherein x + y + z is 100, y is 50-51, z is 15-25, a is 0-1.5, and the rest is x.

2. The method for preparing the NiTiHfSc high temperature shape memory alloy according to claim 1, comprising the steps of:

step one, according to the mass ratio of Ti: ni: hf: weighing Ti, Ni, Hf and Sc according to the proportion of y to z to a, wherein x + y + z is 100, y is 50-51, z is 15-25, and a is 0-1.5;

step two, putting the raw materials weighed in the step one into a non-consumable vacuum arc furnace, and vacuumizing to ensure that the vacuum degree of the back bottom reaches 2 multiplied by 10^-2～2×10^-3Pa, then introducing high-purity argon to the pressure in the furnace of 300-500Pa, smelting the raw materials into a button-shaped ingot by using a high-temperature electric arc, then overturning, and repeatedly smelting for 6-8 times;

step three, putting the button-shaped cast ingot obtained in the step two into a vacuum furnace, and vacuumizing to ensure that the vacuum degree reaches 4 multiplied by 10^-2Pa, keeping the temperature at 900-1100 ℃ for 3h to obtain Ti_x-aNi_yHf_zSc_aHigh temperature shape memory alloys.

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