CN115927915B - Ti-Ni-Zr shape memory alloy and preparation method thereof - Google Patents

Abstract

The present invention belongs to the technical field of Ti-Ni-based shape memory alloys, and particularly relates to a Ti-Ni-Zr shape memory alloy and a preparation method thereof, which solves the problems of high cost, poor machinability, poor controllability of phase transition temperature, memory characteristics, and mechanical properties of existing Ti-Ni-based shape memory alloys. The alloy is special in that the ratio by atomic percentage is: Ni 50.5% to 50.8%; Zr 0.1% to 1.0%; the rest is Ti. The preparation method is special in that it includes the following steps: Step 1: weigh Ti, Ni and Zr by atomic percentage and mix them evenly to obtain a batch; Step 2: put the batch into a medium-frequency vacuum induction furnace to melt an ingot blank; Step 3: put the ingot blank into a vacuum furnace to evacuate and homogenize at high temperature to obtain a forging blank; Step 4: forge, roll and draw the forging blank to obtain an alloy profile; Step 5: heat treatment to obtain a finished shape memory alloy material.

Description

Ti-Ni-Zr shape memory alloy and preparation method thereof

Technical Field

The invention belongs to the technical field of Ti-Ni based shape memory alloys, and in particular relates to a Ti-Ni-Zr shape memory alloy and a preparation method thereof.

Background technique

Since its discovery, Ti-Ni based shape memory alloys have shown extraordinary application value. With the in-depth research and transformation of results in recent years, a variety of shape memory alloy products have appeared on the market, with applications in aerospace, biomedicine, mechanical electronics, chemical energy and other engineering and civil fields.

Although Ti-Ni shape memory alloy has many advantages, it also has the problems of high raw material cost, difficult processing and its own performance is affected by alloy composition, processing technology, heat treatment process, deformation temperature, etc. In order to improve the performance of Ti-Ni shape memory alloy and reduce the cost, people have conducted research from the aspects of alloy composition, heat treatment process and experimental conditions. Among them, Ti-Ni alloy as the matrix has been widely used to improve its performance by doping the third component and assisting with heat treatment process.

However, some of the existing Ti-Ni-based shape memory alloys doped with a third component have good machinability but high cost; some have low cost but poor machinability; and their phase transition temperature, memory characteristics, and mechanical properties are poorly controllable.

Summary of the invention

The purpose of the present invention is to provide a Ti-Ni-Zr shape memory alloy and a preparation method thereof, so as to solve the technical problems of the existing Ti-Ni based shape memory alloy having high cost, poor machinability, and poor controllability of phase transition temperature, memory characteristics and mechanical properties.

The technical solution adopted by the present invention is a Ti-Ni-Zr shape memory alloy, which is special in that the atomic percentage ratio is:

Ni: 50.5%～50.8%;

Zr: 0.1%～1.0%;

The rest are Ti.

Furthermore, the chemical formula of the alloy is Ti _49.1 Ni _50.8 Zr _0.1 . The Ti _49.1 Ni _50.8 Zr _0.1 shape memory alloy has good hot and cold processing properties, and its martensitic reverse phase transformation end temperature Af after complete annealing is about -17°C; after low-temperature annealing, its tensile strength is 1136MPa to 1489MPa, and its elongation is 11.6% to 13.3%. After high-temperature annealing, its superelastic stress platform is about 500MPa, and its superelastic strain exceeds 7%; its functional characteristic parameters can fully meet the needs of practical applications.

The present invention also provides a method for preparing the above-mentioned Ti-Ni-Zr shape memory alloy, which is special in that it comprises the following steps:

Step 1: weigh Ti, Ni and Zr raw materials according to the atomic percentage ratio, and mix the weighed raw materials evenly to obtain an alloy ingredient;

Step 2: placing the alloy ingredients obtained in step 1 into a medium frequency vacuum induction furnace to smelt a Ti-Ni-Zr alloy ingot;

Step 3: Place the Ti-Ni-Zr alloy ingot obtained by smelting in step 2 into a vacuum furnace, evacuate the furnace, and make the vacuum degree less than 1×10 ^-2 Pa; then carry out high temperature homogenization treatment at 850°C to 1050°C for 6h to 12h; finally, remove the surface oxide scale and riser by machining to obtain the Ti-Ni-Zr alloy forging billet;

Step 4: Forging the Ti-Ni-Zr alloy forging blank obtained in step 3, or forging first and then rolling, or forging, rolling and drawing in sequence, to obtain a Ti-Ni-Zr shape memory alloy profile;

Step 5: The Ti-Ni-Zr shape memory alloy profile obtained in step 4 is subjected to annealing treatment at 350°C to 700°C, or solution treatment at 750°C to 850°C, or solution treatment at 750°C to 850°C and then aging treatment at 300°C to 600°C to obtain a finished Ti-Ni-Zr shape memory alloy material. The preparation of the Ti-Ni-Zr shape memory alloy is completed.

Furthermore, in order to reduce the impurities in the prepared Ti-Ni-Zr shape memory alloy material, the purity of the Ti, Ni and Zr raw materials described in step 1 is: Ti≥99.9wt.%, Ni≥99.99wt.%, Zr≥99.9wt.%.

Furthermore, in order to improve the purity and uniformity of the Ti-Ni-Zr alloy ingot obtained by smelting, when the alloy ingredients obtained in step one are placed in a medium frequency vacuum induction furnace for smelting in step two, the vacuum degree is less than 1×10 ^-3 Pa, the smelting temperature is controlled at 1250°C to 1360°C, the smelting time is controlled at 15min to 25min, and the crucible used is a water-cooled copper crucible with a crucible diameter of 100mm to 300mm.

Furthermore, the forging temperature in step 4 is controlled at 750°C to 900°C.

Furthermore, the rolling temperature in step 4 is controlled at 750°C to 900°C.

The forging and rolling temperatures in step 4 are controlled at 750°C to 900°C. The temperature is controlled within such a range because: if the temperature is too high, some coarse precipitation phases will be formed inside the material, and the oxidation of the material will be aggravated, which will eventually reduce the forging and rolling properties of the material, and increase the impurity elements in the alloy, which is not conducive to the control of the alloy composition; if the temperature is too low, the material strength will be too high and the machinability will be insufficient. At the same time, the alloy is sensitive to cracks, and if the temperature is too low, the material will crack during forging and rolling.

Furthermore, the rolling in step 4 is hot rolling, or hot rolling followed by crystallization annealing and then cold rolling.

Furthermore, the drawing in step 4 is hot drawing, or first hot drawing and then cold drawing;

The hot drawing temperature is controlled at 600° C. to 850° C.;

In the cold drawing, an intermediate annealing treatment at 650° C. to 800° C. is required when the total deformation reaches 40% to 55%.

In this way, the drawing method can be selected according to the required finished product size specifications. For example, when the required finished product diameter is 4mm to 6mm, a separate hot drawing method can be selected; when the required finished product diameter is 0.5mm to 2mm, a hot drawing method can be selected first, and then a cold drawing method can be selected; cold drawing can improve the performance of the material, and improve the hardness, tensile strength, superelasticity, and memory properties of the material. The reason why the hot drawing temperature should be controlled within a temperature range of 600℃ to 850℃ is that at 600℃ to 850℃, the material is in a recrystallization annealing state, the material has better plasticity, good processability, and is easy to deform, which is conducive to drawing. The reason why an intermediate annealing treatment at 650℃~800℃ is required when the total deformation reaches 40%~55% during cold drawing is that when the total deformation reaches 40%~55%, the material is too hard and difficult to draw. An intermediate annealing treatment at 650℃~800℃ can soften the material and facilitate drawing. If an intermediate annealing treatment at 650℃~800℃ is carried out when the total deformation is too small, the drawing efficiency will be too low.

Furthermore, the heating equipment used in the forging, rolling and drawing process in step 4 is a resistance furnace. In this way, it can be avoided that when using a gas furnace for heating, impurities containing carbon, hydrogen, oxygen and other elements generated by the combustion of gas enter the material at high temperature. If these impurities enter, the impurities in the material will increase, the alloy composition will change, and the alloy performance will deteriorate.

The beneficial effects of the present invention are:

(1) The Ti-Ni-Zr shape memory alloy of the present invention has an atomic percentage ratio of: Ni: 50.5% to 50.8%; Zr: 0.1% to 1.0%; the rest is Ti. It can be seen from the atomic percentage ratio that the Ti-Ni-Zr shape memory alloy of the present invention belongs to a Ni-rich Ti-Ni shape memory alloy. The Ni-rich Ti-Ni shape memory alloy has better memory properties than the Ni-poor Ti-Ni shape memory alloy and the Ti-Ni shape memory alloy with a nearly equal atomic ratio, and its properties are easier to control; the Ni-poor Ti-Ni alloy does not have Ni-rich precipitates such as Ti ₃ Ni ₄ after heat treatment, so the heat treatment has little effect on its microstructure and phase transformation behavior, and thus the potential for improving its performance through heat treatment is not great; while the Ni-rich Ti-Ni alloy can precipitate a Ti ₃ Ni ₄ phase coherent with the matrix in the microstructure after heat treatment, and the appearance of this phase is beneficial to improving the strength of the alloy on the one hand, and on the other hand, it can reduce the Ni content in the matrix, thereby affecting the phase transformation temperature and deformation behavior of the alloy. Therefore, if you want to obtain a ternary shape memory alloy with adjustable phase transition temperature, memory characteristics and mechanical properties, it is more appropriate to add a third component to the Ni-rich Ti-Ni alloy. The present invention adds Zr to the Ni-rich Ti-Ni alloy. During the preparation process, the Ti-Ni-Zr shape memory alloy profile obtained after the alloy is subjected to plastic processing can be matched with heat treatment of different systems to regulate the phase transition temperature, memory behavior and tensile strength of the alloy; at the same time, Zr is cheap, and the cold and hot processing performance of the alloy of a specific component is good. After adding a small amount of Zr to the Ni-rich Ti-Ni alloy, the phase transition temperature of the alloy first decreases and then increases, and the strength, elongation, shape memory recovery rate and other properties are improved; therefore, the Ti-Ni-Zr shape memory alloy of the present invention has a low preparation cost, good processability and good memory characteristics; therefore, the present invention solves the technical problems of the existing Ti-Ni-based shape memory alloy having high cost, poor processability, poor controllability of phase transition temperature, memory characteristics and mechanical properties. The Ti-Ni-Zr shape memory alloy of the present invention is a Ti-Ni-based shape memory alloy with great application prospects.

(2) The chemical formula of the Ti-Ni-Zr shape memory alloy of the present invention is preferably Ti _49.1 Ni _50.8 Zr _0.1 . The Ti _49.1 Ni _50.8 Zr _0.1 shape memory alloy has good hot and cold processing properties, and its martensitic reverse transformation end temperature Af after complete annealing is about -17°C; after low-temperature annealing, its tensile strength is 1136MPa to 1489MPa, and its elongation is 11.6% to 13.3%. After high-temperature annealing, its superelastic stress platform is about 500MPa, and its superelastic strain exceeds 7%; its functional characteristic parameters can fully meet the needs of practical applications.

(3) The Ti-Ni-Zr shape memory alloy is prepared by the preparation method of the Ti-Ni-Zr shape memory alloy of the present invention, and the process is simple; the prepared Ti-Ni-Zr shape memory alloy has good plastic processing ability and good memory characteristics, and its maximum superelastic strain exceeds 7%; in the preparation process, the Ti-Ni-Zr shape memory alloy profile obtained by plastic processing (forging in step 4, or forging first and then rolling, or forging, rolling and drawing in sequence) of the alloy is combined with different systems of heat treatment (annealing treatment at 350°C to 700°C in step 5, or solution treatment at 750°C to 850°C, or solution treatment at 750°C to 850°C and then aging treatment at 300°C to 600°C) to adjust the phase transition temperature, superelasticity, memory effect, mechanical properties and microstructure of the final Ti-Ni-Zr shape memory alloy material product.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a microstructure photograph of a Ti _49.1 Ni _50.8 Zr _0.1 shape memory alloy prepared in Example 1 of the present invention; other preparation conditions of (a), (b), (c), and (d) in FIG. 1 are the same, except that the annealing temperature in step 5 is different, wherein:

(a) Annealing temperature is 400°C;

(b) Annealing temperature is 500°C;

(c) annealing temperature is 600°C;

(d) Annealing temperature is 700°C;

FIG2 is a tensile strength and elongation curve of the Ti _49.1 Ni _50.8 Zr _0.1 shape memory alloy prepared in Example 1 of the present invention;

3 is a superelasticity and memory effect curve of the Ti _49.1 Ni _50.8 Zr _0.1 shape memory alloy prepared in Example 1 of the present invention;

FIG4 is a phase change behavior curve of the Ti 49.1 Ni 50.8 Zr 0.1 shape memory alloy prepared by changing the heat treatment system in step 5 of Example 1 of the present invention from annealing at ₃₅₀ °C to 700°C to first solutionizing at 800°C for 1h, water cooling, and then aging at 300°C _{to 600} °C for 1h to 50h, while other preparation steps remain unchanged; other preparation conditions in (e) and (f) of FIG4 are the same, only the temperature of aging treatment in step 5 is different, wherein:

(e) Aging treatment temperature is 400°C;

(f) Aging treatment temperature is 500°C;

FIG5 is a mechanical property curve of the Ti _48.5 Ni _50.5 Zr ₁ shape memory alloy prepared in Example 2 of the present invention;

FIG. 6 is a superelastic characteristic curve of the Ti _48.8 Ni _50.7 Zr _0.5 shape memory alloy prepared in Example 3 of the present invention.

Detailed ways

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

The invention discloses a Ti-Ni-Zr shape memory alloy, which comprises the following atomic percentage ratios: Ni: 50.5%-50.8%; Zr: 0.1%-1.0%; and the rest being Ti.

The Ti-Ni-Zr shape memory alloy of the present invention has a preferred chemical formula of Ti _49.1 Ni _50.8 Zr _0.1 . The Ti _49.1 Ni _50.8 Zr _0.1 shape memory alloy has good hot and cold processing properties, and its martensitic reverse phase transformation end temperature Af after complete annealing is about -17°C; its tensile strength after low-temperature annealing is 1136MPa-1489MPa, and its elongation is 11.6%-13.3%, and its superelastic stress platform after high-temperature annealing is about 500MPa, and its superelastic strain exceeds 7%; its functional characteristic parameters can fully meet the needs of practical applications.

The present invention also provides a method for preparing the above Ti-Ni-Zr shape memory alloy, comprising the following steps:

Step 1: weigh Ti, Ni and Zr raw materials according to the above atomic percentage ratio, and mix the weighed raw materials evenly to obtain an alloy ingredient;

Step 2: placing the alloy ingredients obtained in step 1 into a medium frequency vacuum induction furnace to smelt a Ti-Ni-Zr alloy ingot;

Step 3: Place the Ti-Ni-Zr alloy ingot obtained by smelting in step 2 into a vacuum furnace, evacuate the furnace, and make the vacuum degree less than 1×10 ^-2 Pa; then carry out high temperature homogenization treatment at 850°C to 1050°C for 6h to 12h; finally, remove the surface oxide scale and riser by machining to obtain the Ti-Ni-Zr alloy forging billet;

Step 4: Forging the Ti-Ni-Zr alloy forging blank obtained in step 3, or forging first and then rolling, or forging, rolling and drawing in sequence, to obtain a Ti-Ni-Zr shape memory alloy profile;

Step 5: The Ti-Ni-Zr shape memory alloy profile obtained in step 4 is subjected to annealing treatment at 350°C to 700°C, or solution treatment at 750°C to 850°C, or solution treatment at 750°C to 850°C and then aging treatment at 300°C to 600°C to obtain a finished Ti-Ni-Zr shape memory alloy material. The preparation of the Ti-Ni-Zr shape memory alloy is completed.

In order to reduce the impurities in the prepared Ti-Ni-Zr shape memory alloy material, preferably, the purity of the Ti, Ni and Zr raw materials mentioned above in step 1 is: Ti≥99.9wt.%, Ni≥99.99wt.%, Zr≥99.9wt.%.

In order to improve the purity and uniformity of the Ti-Ni-Zr alloy ingot obtained by smelting, when the alloy ingredients obtained in step 1 are placed in a medium frequency vacuum induction furnace for smelting in the above step 2, preferably the vacuum degree is less than 1×10 ^-3 Pa, the smelting temperature is controlled at 1250°C to 1360°C, the smelting time is controlled at 15min to 25min, and the crucible used is a water-cooled copper crucible with a crucible diameter of 100mm to 300mm.

Preferably, the forging temperature in the above step 4 is controlled at 750°C to 900°C. The rolling temperature in the above step 4 is controlled at 750°C to 900°C. The rolling is hot rolling, or hot rolling followed by re-crystallization annealing and then cold rolling. The reason why the forging and rolling temperatures in step 4 are controlled within the range of 750°C to 900°C is that: if the temperature is too high, some coarse precipitates will be formed inside the material, and the oxidation of the material will also be aggravated, which will eventually reduce the forging and rolling properties of the material, and increase the impurity elements of the alloy, which is not conducive to the control of the alloy composition; if the temperature is too low, the material strength will be too large and the machinability will be insufficient. At the same time, the alloy is sensitive to cracks, and if the temperature is too low, the material will be forged and rolled.

Preferably, the drawing in the above step 4 is hot drawing, or hot drawing first and then cold drawing; the hot drawing temperature is controlled at 600℃～850℃; in cold drawing, an intermediate annealing treatment at 650℃～800℃ is required when the total deformation reaches 40%～55%. In this way, the drawing method can be selected according to the required finished product size specifications. For example, when the required finished product diameter is 4mm～6mm, a separate hot drawing method can be selected; when the required finished product diameter is 0.5mm～2mm, a hot drawing method can be selected first and then cold drawing; cold drawing can improve the performance of the material, so that the material hardness, tensile strength, superelasticity and memory properties are all improved. The reason why the hot drawing temperature is controlled within a temperature range of 600℃～850℃ is that at 600℃～850℃, the material is in a recrystallization annealing state, the material has good plasticity, good processability, easy deformation, and is conducive to drawing. The reason why an intermediate annealing treatment at 650℃~800℃ is required when the total deformation reaches 40%~55% during cold drawing is that when the total deformation reaches 40%~55%, the material is too hard and difficult to draw. An intermediate annealing treatment at 650℃~800℃ can soften the material and facilitate drawing. If an intermediate annealing treatment at 650℃~800℃ is carried out when the total deformation is too small, the drawing efficiency will be too low.

The heating equipment used in the forging, rolling and drawing process in the above step 4 is preferably a resistance furnace. In this way, it can be avoided that when using a gas furnace for heating, impurities containing carbon, hydrogen, oxygen and other elements generated by the combustion of gas enter the material at high temperature. If these impurities enter, the impurities in the material will increase, the alloy composition will change, and the alloy performance will deteriorate.

Embodiment 1:

A method for preparing a Ti _49.1 Ni _50.8 Zr _0.1 shape memory alloy wire comprises the following steps:

Step 1: Based on the total weight of 15 kg of Ti _49.1 Ni _50.8 Zr _0.1 shape memory alloy, zirconium with a purity of 99.9 wt.%, nickel with a purity of 99.99 wt.%, and titanium with a purity of 99.9 wt.% are weighed according to a ratio of 0.1 at.% Zr, 50.8 at.% Ni, and 49.1 at.% Ti, wherein the sum of the atomic percentages of Zr, Ni, and Ti is 100%, and the weighed raw materials are evenly mixed to obtain an alloy ingredient;

Step 2: Put the alloy ingredients obtained in step 1 into a medium frequency vacuum induction furnace, evacuate the furnace to a vacuum degree of 0.5×10 ^-3 Pa, and introduce argon gas for protection. Heat the melting temperature to 1360°C, refine for 15 minutes, and cool to obtain a Ti _49.1 Ni _50.8 Zr _0.1 alloy ingot blank; the weight of the alloy ingot blank is about 15kg;

Step 3: placing the Ti _49.1 Ni _50.8 Zr _0.1 alloy ingot obtained by smelting in step 2 into a vacuum furnace, evacuating the furnace to a vacuum degree of 0.2×10 ^-2 Pa, and then maintaining the furnace at 900°C for 10 hours for high temperature homogenization treatment. After the maintenance time is up, the furnace is cooled, and after being taken out of the furnace, the surface oxide scale, defects and risers are removed by machining to obtain a Ti _49.1 Ni _50.8 Zr _0.1 alloy forging billet;

Step 4: heating the Ti _49.1 Ni _50.8 Zr _0.1 alloy forging billet obtained in step 3 to 850°C, keeping it warm for 4 hours, forging it first and then rolling it into an alloy wire billet with a diameter of 9 mm; hot drawing the alloy wire billet with a diameter of 9 mm, the hot drawing temperature is 700°C, and the deformation amount per pass is controlled at 10% to 20%, until it is drawn to a diameter of 3 mm, and then cold drawing is performed. During the cold drawing, an intermediate annealing treatment at 700°C is performed when the total deformation amount reaches 40% to 55%, and finally processed into a Ti _49.1 Ni _50.8 Zr _0.1 shape memory alloy wire profile with a diameter of 1 mm;

Step 5: annealing the Ti _49.1 Ni _50.8 Zr _0.1 shape memory alloy wire profile obtained in step 4 at 350°C-700°C for 20 minutes, and cooling in the furnace to obtain a finished Ti _49.1 Ni _50.8 Zr _0.1 shape memory alloy wire, and the preparation of the Ti _49.1 Ni _50.8 Zr _0.1 shape memory alloy is completed.

The finished product of the Ti _49.1 Ni _50.8 Zr _0.1 shape memory alloy material prepared in Example 1 was used as a sample for microstructure observation, mechanical property and memory property test. Figure 1 is a microstructure photo of the sample. From (a), (b), (c) and (d) in Figure 1, it can be seen that as the annealing temperature increases, the structure of the alloy changes from fibrous to equiaxed; Figure 2 is a tensile strength and elongation curve of the sample. From Figure 2, it can be seen that as the annealing temperature increases, the tensile strength R _m and elongation δ of the alloy are changing; Figure 3 is a superelasticity and memory effect curve of the sample. From Figure 3, it can be seen that as the annealing temperature increases, the alloy characteristics first change from superelasticity to shape memory effect and then to superelasticity, and the platform stress of the alloy first decreases and then increases.

FIG4 is a phase transformation behavior curve of the Ti 49.1 Ni 50.8 Zr 0.1 shape memory alloy prepared by changing the heat treatment system in step 5 of the above embodiment 1 from annealing at 350°C to 700°C to first performing solution treatment at 800°C for 1h, water cooling, and then performing aging at 300 _° C _{to 600} °C for 1h to 50h, while other preparation steps remain unchanged; other preparation conditions in (e) and (f) in FIG4 are the same, only the aging treatment temperature in step 5 is different, wherein: (e) the aging treatment temperature is 400°C; (f) the aging treatment temperature is 500°C; after aging for 1h to 50h, the phase transformation behavior is tested on a NETZSCH DSC, and FIG4 is a phase transformation behavior curve, wherein M in FIG4 represents martensite, R represents R phase, R' represents R reverse phase transformation, and A represents austenite; it can be seen from FIG4 that the phase transformation behavior and phase transformation temperature of the alloy change continuously with the increase of aging temperature and the extension of aging time. Compared with the heat treatment system of only solution treatment, the heat treatment system of first solution treatment and then aging treatment will cause Ni-rich phase to precipitate inside the alloy after aging, and the appearance of this precipitated phase will affect the phase transition temperature, memory characteristics and mechanical properties of the alloy.

In summary, Ti _49.1 Ni _50.8 Zr _0.1 shape memory alloy has good hot and cold workability, and its microstructure, memory behavior (superelasticity and memory effect) and phase transition temperature can be regulated by combining different heat treatment systems after drawing. That is, the alloy is a TiNi-based shape memory alloy with good application prospects.

Embodiment 2:

A method for preparing a Ti _48.5 Ni _50.5 Zr ₁ shape memory alloy wire comprises the following steps:

Step 1: Based on the total weight of 25 kg of Ti _48.5 Ni _50.5 Zr ₁ shape memory alloy, zirconium with a purity of 99.9 wt.%, nickel with a purity of 99.99 wt.%, and titanium with a purity of 99.9 wt.% are weighed according to a ratio of 1 at.% Zr, 50.5 at.% Ni, and 48.5 at.% Ti, wherein the sum of the atomic percentages of Zr, Ni, and Ti is 100%, and the weighed raw materials are uniformly mixed to obtain an alloy ingredient;

Step 2: Place the alloy ingredients obtained in step 1 into a medium frequency vacuum induction furnace, evacuate to a vacuum degree of 0.7×10 ^-3 Pa, and then introduce argon protection. Heat the melting temperature to 1320°C, refine for 25 minutes, and cool to obtain a Ti _48.5 Ni _50.5 Zr ₁ alloy ingot billet, the weight of the alloy ingot billet is about 25Kg;

Step 3: placing the Ti _48.5 Ni _50.5 Zr ₁ alloy ingot obtained by smelting in step 2 into a vacuum furnace, evacuating the furnace to a vacuum degree of 0.4×10 ^-2 Pa, and then maintaining the temperature at 950°C for 6 hours for high temperature homogenization treatment. After the maintenance time is up, the furnace is cooled, and after being taken out of the furnace, the surface oxide scale, defects and risers are removed by machining to obtain a Ti _48.5 Ni _50.5 Zr ₁ alloy forging billet;

Step 4: heating the Ti _48.5 Ni _50.5 Zr ₁ alloy forging billet obtained in step 3 to 800° C., keeping the temperature for 10 hours, forging and then rolling it into an alloy wire billet with a diameter of 9 mm; hot drawing the alloy wire billet with a diameter of 9 mm, the hot drawing temperature is 750° C., and the deformation amount per pass is controlled at 10% to 20%, until it is drawn to a diameter of 3 mm, and then cold drawing is performed. During the cold drawing, an intermediate annealing treatment at 700° C. is performed when the total deformation amount reaches 40% to 55%, and finally processed into a Ti _48.5 Ni _50.5 Zr ₁ shape memory alloy wire profile with a diameter of 0.8 mm;

Step 5: The Ti _48.5 Ni _50.5 Zr ₁ shape memory alloy wire obtained in step 4 is annealed at 650° C. for 20 min, and then cooled in the furnace to obtain a finished Ti _48.5 Ni _50.5 Zr ₁ shape memory alloy wire. The preparation of the Ti _48.5 Ni _50.5 Zr ₁ shape memory alloy is completed.

The finished Ti _48.5 Ni _50.5 Zr ₁ shape memory alloy wire prepared in the above Example 2 was used as a sample to test its mechanical properties. Figure 5 is a mechanical property curve of the Ti _48.5 Ni _50.5 Zr ₁ shape memory alloy prepared in Example 2 of the present invention. It can be seen from Figure 5 that the tensile strength of the Ti _48.5 Ni _50.5 Zr ₁ alloy after recrystallization annealing is 1004 MPa, and the elongation is as high as 30.1%, showing excellent strong plasticity.

Embodiment 3:

A method for preparing a Ti _48.8 Ni _50.7 Zr _0.5 shape memory alloy wire comprises the following steps:

Step 1: Based on the total weight of 20 kg of Ti _48.8 Ni _50.7 Zr _0.5 shape memory alloy, zirconium with a purity of 99.9 wt.%, nickel with a purity of 99.99 wt.%, and titanium with a purity of 99.9 wt.% are weighed according to a ratio of 0.5 at.% Zr, 50.7 at.% Ni, and 48.8 at.% Ti, wherein the sum of the atomic percentages of Zr, Ni, and Ti is 100%, and the weighed raw materials are evenly mixed to obtain an alloy ingredient;

Step 2: Put the alloy ingredients obtained in step 1 into a medium frequency vacuum induction furnace, evacuate to a vacuum degree of 0.9×10 ^-3 Pa, and then introduce argon protection. Heat the melting temperature to 1340°C, refine for 20 minutes, and cool to obtain a Ti _48.8 Ni _50.7 Zr _0.5 alloy ingot billet, the weight of the alloy ingot billet is about 20Kg;

Step 3: placing the Ti _48.8 Ni _50.7 Zr _0.5 alloy ingot obtained by smelting in step 2 into a vacuum furnace, evacuating the furnace to a vacuum degree of 0.4×10 ^-2 Pa, then maintaining the furnace at 940°C for 8 hours for high temperature homogenization treatment, cooling the furnace after the holding time is up, and removing the surface oxide scale, defects and risers by machining after taking out of the furnace to obtain a Ti _48.8 Ni _50.7 Zr _0.5 alloy forging billet;

Step 4: Heat the Ti _48.8 Ni _50.7 Zr _0.5 alloy forging billet obtained in step 3 to 870°C, keep it warm for 7 hours, forge it and then roll it into an alloy wire billet with a diameter of 9 mm; hot draw the alloy wire billet with a diameter of 9 mm, the hot drawing temperature is 810°C, and the deformation amount per pass is controlled at 10% to 20%, until it is drawn to a diameter of 3 mm, and then cold drawing is performed. During the cold drawing, an intermediate annealing treatment at 740°C is required when the total deformation amount reaches 40% to 55%, and finally processed into a Ti _48.8 Ni _50.7 Zr _0.5 shape memory alloy wire profile with a diameter of 0.5 mm.

Step 5: The Ti _48.8 Ni _50.7 Zr _0.5 shape memory alloy wire profile obtained in step 4 is annealed at 450° C. for 20 min, and then cooled in the furnace to obtain a finished Ti _48.8 Ni _50.7 Zr _0.5 shape memory alloy wire. The preparation of the Ti _48.8 Ni _50.7 Zr _0.5 shape memory alloy is completed.

The finished Ti _48.8 Ni _50.7 Zr _0.5 shape memory alloy wire prepared in the above Example 3 was used as a sample to test its superelastic properties. FIG6 is a superelastic characteristic curve of the Ti _48.8 Ni _50.7 Zr _0.5 shape memory alloy prepared in Example 3 of the present invention. It can be seen from FIG6 that the superelastic yield platform of the Ti _48.8 Ni _50.7 Zr _0.5 alloy after low-temperature annealing is as high as 612 MPa, the superelastic strain is as high as 8%, and the superelastic residual strain is only 0.1%. The alloy exhibits excellent superelastic properties.

It can be seen from the above three embodiments that the Ti-Ni-Zr (50.5at.% to 50.8at.% Ni, 0.1at.% to 1.0at.% Zr, and the rest Ti) shape memory alloy has good hot and cold workability, and its microstructure, memory behavior (superelasticity and memory effect), and phase transition temperature can be regulated by drawing and combining different heat treatment systems to obtain a Ti-Ni-Zr shape memory alloy with excellent performance, that is, the alloy is a TiNi-based shape memory alloy with good application prospects.

Claims (6)

1. A Ti-Ni-Zr shape memory alloy, characterized in that the atomic percentage ratio is: Ni: 50.5%~50.8%; Zr: 0.1%~1.0%; The rest are Ti; The preparation method of the Ti-Ni-Zr shape memory alloy comprises the following steps: Step 1: weigh Ti, Ni and Zr raw materials according to the atomic percentage ratio, and mix the weighed raw materials evenly to obtain an alloy ingredient; Step 2: placing the alloy ingredients obtained in step 1 into a medium frequency vacuum induction furnace to smelt a Ti-Ni-Zr alloy ingot; Step 3: Place the Ti-Ni-Zr alloy ingot obtained by smelting in step 2 into a vacuum furnace, evacuate the furnace, and make the vacuum degree less than 1×10 ^-2 Pa; then carry out high temperature homogenization treatment at 850°C to 1050°C for 6h to 12h; finally, remove the surface oxide scale and riser by machining to obtain the Ti-Ni-Zr alloy forging billet; Step 4: Forging the Ti-Ni-Zr alloy forging blank obtained in step 3, or forging first and then rolling, or forging, rolling and drawing in sequence, to obtain a Ti-Ni-Zr shape memory alloy profile; Step 5: performing annealing treatment at 350°C to 700°C on the Ti-Ni-Zr shape memory alloy profile obtained in step 4, or performing solid solution treatment at 750°C to 850°C, or first performing solid solution treatment at 750°C to 850°C and then performing aging treatment at 300°C to 600°C to obtain a finished Ti-Ni-Zr shape memory alloy material, and the preparation of the Ti-Ni-Zr shape memory alloy is completed; In step 2, when the alloy ingredients obtained in step 1 are placed in a medium frequency vacuum induction furnace for smelting, the vacuum degree is less than 1×10 ^-3 Pa, the smelting temperature is controlled at 1250° C. to 1360° C., the smelting time is controlled at 15 min to 25 min, and the crucible used is a water-cooled copper crucible with a crucible diameter of 100 mm to 300 mm; The drawing in step 4 is hot drawing, or first hot drawing and then cold drawing; The hot drawing temperature is controlled at 600°C to 850°C; In the cold drawing, an intermediate annealing treatment at 650° C. to 800° C. is required when the total deformation reaches 40% to 55%. 2. The Ti-Ni-Zr shape memory alloy according to claim 1, characterized in that the purity of the Ti, Ni and Zr raw materials described in step 1 is: Ti ≥ 99.9wt.%, Ni ≥ 99.99wt.%, and Zr ≥ 99.9wt.%. 3. The Ti-Ni-Zr shape memory alloy according to claim 1, characterized in that the forging temperature in step 4 is controlled at 750°C to 900°C. 4. The Ti-Ni-Zr shape memory alloy according to claim 1, characterized in that the rolling temperature in step 4 is controlled at 750°C to 900°C. 5. The Ti-Ni-Zr shape memory alloy according to claim 1, characterized in that: the rolling in step 4 is hot rolling, or hot rolling followed by crystallization annealing and then cold rolling. 6. The Ti-Ni-Zr shape memory alloy according to any one of claims 1 to 5, characterized in that the heating equipment used in the forging, rolling and drawing processes in step 4 is a resistance furnace.