High-temperature shape memory alloy with two-way effect and preparation method thereof

Abstract

The invention provides a high-temperature shape memory alloy with a two-way effect and a preparation method of the high-temperature shape memory alloy, and relates to the field of shape memory alloys. The high-temperature shape memory alloy is NiTiHfNb high-temperature shape memory alloy, the chemical formula of the high-temperature shape memory alloy is (NiaTi100-a-bHfb) 100-cNbc, the value of a ranges from 45 to 49.9, the value of b ranges from 15.1 to 20, and the value of c ranges from 5 to 14.9; during preparation, the NiTiHfNb high-temperature shape memory alloy is obtained by sequentially smelting, hot forging, hot rolling, cold rolling or drawing and heat treatment after corresponding metals are weighed according to the chemical components, and the heat treatment conditions are that the temperature is 400-900 DEG C, and the time is 10 minutes to 120 hours. According to the invention, the quaternary shape memory alloy is prepared by introducing a fourth alloy element Nb, the material not only presents a higher phase transition temperature, but also the toughness and machinability of the material can be effectively improved by regulating and controlling the form and distribution of the Nb phase through heat treatment.

Description

Technical Field

[0001] The invention relates to the technical field of shape memory alloys, and in particular to a high-temperature shape memory alloy with a two-way effect and a preparation method thereof. Background Art

[0002] Shape memory alloys are widely used in industrial intelligence, aerospace, automotive industry, medical equipment and other fields due to their excellent characteristics such as shape memory effect, superelasticity, and integrated sensing and driving. They are used as pipe fittings, unlocking structures, drivers, interventional stents, artificial joints and dental orthopedic wires, etc., and have high commercial value.

[0003] With the widespread application of shape memory alloys in the market, more and more work scenarios consider using shape memory alloys as core components, such as high-temperature work scenarios. At present, the phase transition temperature of the most widely used NiTi shape memory alloy on the market is lower than 100°C, which makes the application scenarios of NiTi shape memory alloys limited to low-temperature environments, such as biomedical implants and drivers, and not suitable for high-temperature work scenarios. High-temperature shape memory alloys have good mechanical properties, corrosion resistance and high-temperature stability, and the application breakthrough of shape memory alloys in high-temperature work scenarios has been achieved. At present, high-temperature shape memory alloys with martensitic phase transition temperatures exceeding 200°C include (Ni-X)Ti series (X=Pt, Pb, Au), Ni(Ti-X) series alloys (X=Hf, Zr), NiAl series alloys and CuAl series alloys, among which NiAl series and CuAl series high-temperature shape memory alloys are not stable enough, and their memory effect will deteriorate sharply with the precipitation of equilibrium phases at high temperatures; NiTiZr and NiTiHf are brittle and difficult to use in practice; although NiTiPd has the best comprehensive performance, the expensive price of Pd element seriously limits its practical use.

[0004] However, with the increasingly stringent operating environment requirements in high-temperature working scenarios, high-temperature shape memory alloys are required to have a higher phase transition temperature. The phase transition temperature of traditional ternary shape memory alloys is limited, and the processing performance of the alloy system is not ideal. Summary of the invention

[0005] The present invention aims to provide a high-temperature shape memory alloy with a two-way effect and a preparation method thereof, and proposes a TiNiNbHf quaternary shape memory alloy. By introducing a fourth alloying element Nb, the high-temperature shape memory alloy system exhibits a higher phase transition temperature, and the toughness and machinability of the material can be effectively improved by regulating the morphology and distribution of the Nb phase through heat treatment.

[0006] To achieve the above object, the present invention proposes the following technical solutions: In the first aspect, a high temperature shape memory alloy with a two-way effect is proposed, wherein the high temperature shape memory alloy is a NiTiHfNb high temperature shape memory alloy, and the chemical formula is: (Ni a Ti 100-a-b Hf b ) 100-c Nb c , wherein the value range of a is 45-49.9, the value range of b is 15.1-20, and the value range of c is 5-14.9; the NiTiHfNb high temperature shape memory alloy is microscopically composed of a matrix NiTiHf(Nb) phase and a short rod-shaped or spherical β-Nb phase, and the β-Nb phase is dispersed in the matrix NiTiHf(Nb) phase.

[0007] Furthermore, the chemical formula of the NiTiHfNb high temperature shape memory alloy is: (Ni 49.5 Ti 35 Hf 15.5 ) 88 Nb 12 .

[0008] Furthermore, the NiTiHfNb high temperature shape memory alloy is made by weighing raw materials according to atomic percentage, and is successively smelted, hot forged, hot rolled, cold rolled or drawn, and heat treated at a temperature of 400-900 o C, time 10min-120h.

[0009] In a second aspect, a method for preparing the high temperature shape memory alloy having a two-way effect as described above is provided, comprising the following steps: 1) According to chemical composition (Ni a Ti 100-a-b Hf b ) 100-c Nb c Weigh Ni, Ti, Hf and Nb as raw materials respectively, wherein the value range of a is 45-49.9, the value range of b is 15.1-20, and the value range of c is 5-14.9; 2) Melting the raw materials to obtain NiTiHfNb alloy ingots; optionally, the melting parameters are a temperature not less than 1500°C and a vacuum degree better than 4×10 -2 Pa, refining time is not less than 20min.

[0010] 3) hot forging the NiTiHfNb alloy ingot to obtain a hot forged NiTiHfNb alloy ingot; wherein the hot forging process parameters are: hot forging temperature 750-1100° C., heat preservation time 3-72 hours; 4) hot rolling or cold rolling the hot forged NiTiHfNb alloy ingot to obtain a hot rolled or cold rolled NiTiHfNb alloy ingot; wherein the process parameters of the hot rolling are: the rolling temperature is 800°C-1050°C; the process parameters of the cold rolling are: multiple annealing treatments and at least one vacuum solution treatment during the cold rolling process; the annealing treatment temperature is 750°C-660°C, and the temperature is kept for 20-30 minutes; the vacuum solution treatment temperature is 850-900°C, and the temperature is kept for 1-2 hours; 5) Drawing the hot-rolled or cold-rolled NiTiHfNb alloy ingot to obtain a drawn NiTiHfNb alloy wire; wherein the drawing process can be performed multiple times, and the drawing and post-drawing annealing processes can be performed according to the prior art.

[0011] 6) heat treating the hot-rolled, cold-rolled or drawn NiTiHfNb alloy wire to obtain a NiTiHfNb high-temperature shape memory alloy; wherein the process parameters of the heat treatment are: a heat treatment temperature of 400-900° C. and a heat treatment time of 10 min-120 h.

[0012] Furthermore, in the NiTiHfNb alloy ingot obtained by smelting in step 2), the β-Nb phase exists in a network form in the matrix NiTiHf(Nb) phase, and the area proportion of the β-Nb phase in the matrix NiTiHf(Nb) phase is 15-45%.

[0013] Furthermore, the network morphology of the β-Nb phase of the NiTiHfNb alloy ingot obtained in step 2) is gradually broken during hot forging, hot rolling or cold rolling, and drawing, and is elongated along the main processing direction.

[0014] Furthermore, in the step 6), the β-Nb phase of the drawn NiTiHfNb alloy wire is transformed into a short rod or spherical shape during the heat treatment process.

[0015] Furthermore, the NiTiHfNb alloy wire after hot rolling, cold rolling or drawing is heat treated at a temperature of 750° C. for 18-24 hours.

[0016] In a third aspect, the present invention proposes the application of the above-mentioned high-temperature shape memory alloy with two-way effect in high-temperature working scenarios.

[0017] It can be seen from the above technical solutions that the technical solutions of the present invention have the following beneficial effects: The invention discloses a high temperature shape memory alloy with a two-way effect and a preparation method thereof. The high temperature shape memory alloy is a NiTiHfNb high temperature shape memory alloy, and the chemical formula is: (Ni a Ti 100-a-b Hf b )100-c Nb c , wherein the value range of a is 45-49.9, the value range of b is 15.1-20, and the value range of c is 5-14.9; during preparation, the corresponding metal is weighed according to the chemical composition and then smelted, hot forged, hot rolled, cold rolled or drawn in sequence, and heat treated to obtain NiTiHfNb high temperature shape memory alloy, and the process parameters of heat treatment are: heat treatment temperature 400-900℃, heat treatment time 10min-120h. The present invention proposes to prepare a quaternary shape memory alloy by introducing a fourth alloy element Nb, which not only presents a higher phase transition temperature, but also can effectively improve the toughness and machinability of the material by regulating the morphology and distribution of the Nb phase through heat treatment.

[0018] The present invention aims to solve the technical problems that the phase transition temperature of traditional ternary shape memory alloys is limited and the processing performance of the alloy system is not ideal; the short rod-shaped or spherical β-Nb phase obtained by heat treatment makes the NiTiHfNb high-temperature shape memory alloy have a wide phase transition strain range, and the interface effect between the short rod-shaped or spherical β-Nb phase in nano form and the matrix NiTiHf (Nb) phase is conducive to the storage of prestress.

[0019] It should be appreciated that all combinations of the foregoing concepts, as well as additional concepts described in greater detail below, may be considered to be part of the inventive subject matter of the present disclosure, provided such concepts are not mutually inconsistent.

[0020] The foregoing and other aspects, embodiments and features of the present invention can be more fully understood from the following description in conjunction with the accompanying drawings. Other additional aspects of the present invention, such as the features and / or beneficial effects of the exemplary embodiments, will be apparent from the following description or learned from the practice of the specific embodiments according to the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings are not drawn to scale according to actual reference objects. In the accompanying drawings, each identical or nearly identical component shown in various figures may be represented by the same reference numeral. For the sake of clarity, not every component is labeled in each figure. Now, embodiments of various aspects of the present invention will be described by way of example and with reference to the accompanying drawings, in which: Figure 1 This is a microscopic scanning electron microscope image of the NiTiHfNb high temperature shape memory alloy prepared in Example 1; Figure 2 This is a stress-strain curve of the NiTiHfNb high temperature shape memory alloy obtained in Example 1; Figure 3 This is a two-way strain effect diagram of the NiTiHfNb high temperature shape memory alloy prepared in Example 1; Figure 4This is a microscopic scanning electron microscope image of the NiTiHfNb high temperature shape memory alloy prepared in Comparative Example 1; Figure 5 This is a microscopic scanning electron microscope image of the NiTiHfNb high temperature shape memory alloy prepared in Comparative Example 2. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein should be the common meaning understood by people with general skills in the field to which the present invention belongs.

[0023] The words "first", "second" and similar words used in the patent application specification and claims of the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, unless the context clearly indicates otherwise, the singular form of "a", "an" or "the" and other similar words do not indicate a quantitative limitation, but indicate the existence of at least one. "Include" or "comprise" and other similar words mean that the elements or objects appearing before "include" or "comprise" cover the features, wholes, steps, operations, elements and / or components listed after "include" or "comprise", and do not exclude the existence or addition of one or more other features, wholes, steps, operations, elements, components and / or their collections. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0024] Based on the limited phase transition temperature of traditional ternary shape memory alloys, and the less than ideal toughness and machinability of the alloys, they fail to meet the application standards in increasingly demanding high-temperature working scenarios; the present invention aims to propose a high-temperature shape memory alloy with a two-way effect and a preparation method thereof, and obtain a TiNiNbHf quaternary shape memory alloy by introducing a fourth metal element, and regulating the micromorphology of the second phase formed by the introduction of the fourth metal element and its proportion in the matrix, so as to adjust the phase transition temperature and machinability of the quaternary shape memory alloy to meet the application requirements of current high-temperature working scenarios.

[0025] Specifically, the high temperature shape memory alloy with two-way effect disclosed in the present invention is a NiTiHfNb high temperature shape memory alloy, and the chemical formula is: (Ni aTi 100-a-b Hf b ) 100-c Nb c , wherein a is in the range of 45-49.9, b is in the range of 15.1-20, and c is in the range of 5-14.9; the NiTiHfNb high temperature shape memory alloy is microscopically composed of a matrix NiTiHf(Nb) phase and a short rod-shaped or spherical β-Nb phase, and the β-Nb phase is dispersed in the matrix NiTiHf(Nb) phase; preferably, the high temperature shape memory alloy is a NiTiHfNb high temperature shape memory alloy with the chemical formula: (Ni 49.5 Ti 35 Hf 15.5 ) 88 Nb 12 .

[0026] The preparation of NiTiHfNb high temperature shape memory alloy includes the following steps: 1) a Ti 100-a- b Hf b ) 100-c Nb c Weigh Ni, Ti, Hf and Nb as raw materials respectively, wherein a is in the range of 45-49.9, b is in the range of 15.1-20, and c is in the range of 5-14.9; 2) smelting the raw materials to obtain a NiTiHfNb alloy ingot, wherein the β-Nb phase in the NiTiHfNb alloy ingot exists in a network form in a matrix NiTiHf(Nb) phase, and the area proportion of the β-Nb phase in the matrix NiTiHf(Nb) phase is 15-45%; 3) hot forging the NiTiHfNb alloy ingot to obtain a hot forged NiTiHfNb alloy ingot; 4) hot rolling or cold rolling the hot forged NiTiHfNb alloy ingot to obtain a hot rolled or cold rolled NiTiHfNb alloy ingot; 5) The hot-rolled or cold-rolled NiTiHfNb alloy ingot is drawn to obtain a drawn NiTiHfNb alloy wire; 6) the hot-rolled, cold-rolled or drawn NiTiHfNb alloy wire is heat-treated, and the β-Nb phase is converted into a short rod or a sphere during the heat treatment process, and finally a NiTiHfNb high-temperature shape memory alloy is obtained; wherein the process parameters of the heat treatment are: a heat treatment temperature of 400-900°C and a heat treatment time of 10min-120h.

[0027] The high temperature shape memory alloy with two-way effect and the preparation method thereof disclosed in the present invention are further specifically introduced below in conjunction with the specific embodiments described in the accompanying drawings.

[0028] Example 1 The preparation process of a high temperature shape memory alloy with two-way effect is as follows: 1) According to the chemical composition (Ni 49.5 Ti 35 Hf 15.5 ) 88 Nb 12 1) Weigh Ni, Ti, Hf and Nb as raw materials respectively; 2) Melt the raw materials to obtain NiTiHfNb alloy material; 3) Hot forge the NiTiHfNb alloy ingot to obtain the hot forged NiTiHfNb alloy material, and cool the hot forged product naturally in the air; 4) Hot roll or cold roll the hot forged NiTiHfNb alloy ingot to obtain the hot rolled or cold rolled NiTiHfNb alloy material, and cool the hot rolled or cold rolled product naturally in the air; 5) Draw the hot rolled or cold rolled NiTiHfNb alloy ingot to obtain the drawn NiTiHfNb alloy wire, and cool the drawn product in a drawing coolant; 6) Heat treat the hot rolled, cold rolled or drawn NiTiHfNb alloy wire to obtain a NiTiHfNb high temperature shape memory alloy, and cool the product in an annealing furnace; wherein the process parameters of the heat treatment are: heat treatment temperature 750°C, heat treatment time 24h.

[0029] The SEM image of the NiTiHfNb high temperature shape memory alloy prepared in this embodiment is as follows: Figure 1 As shown, image analysis software was used to analyze the proportion of each phase in the image, and the area proportion of the β-Nb phase was 30%.

[0030] The difference between Example 2-5 and Example 1 is that the chemical composition of the prepared NiTiHfNb high temperature shape memory alloy is different, as shown in Table 1 below.

[0031] Table 1 Alloy composition and area ratio of β-Nb phase in each example

[0032] Comparative Examples 1 and 2 are based on Example 1, and the difference from Example 1 is that the heat treatment time is different, as shown in Table 1; In addition, the SEM images of the NiTiHfNb high temperature shape memory alloys prepared in Comparative Examples 1 and 2 are shown in Table 4 and Figure 5 As shown in the figure; when the heat treatment temperature is lower than 400℃, the spheroidization power of β-Nb phase is insufficient, and no obvious spheroidization can be observed in the product scanning electron microscope image; when the heat treatment temperature is higher than 900℃, the β-Nb phase disappears; when the heat treatment time is shorter than 10min, as shown in the figure Figure 4 The β-Nb phase spheroidization has not started; Figure 5 As shown in the figure, when the heat treatment time is longer than 120h, the wire will be oxidized and the material will be damaged.

[0033] The martensitic phase transition temperatures (Ms) of the alloys prepared in Examples 1-5, Comparative Example 1, and Comparative Example 2 were measured respectively, as shown in Table 2. Under the premise that the alloy has a high phase transition temperature, the present invention further introduces an internal stress field into the prepared NiTiHfNb high temperature shape memory alloy by pre-stretching, and performs a two-way effect test on this basis. Specifically, the stress-strain curve and two-way effect test data of the NiTiHfNb high temperature shape memory alloy prepared in Example 1 are collected, and the results are as follows: Figure 2 and Figure 3 As shown. The test conditions for introducing the internal stress field by pre-stretching are as follows: set the pre-strain amount to 10%-28%, the original gauge length of the product to 100mm, the chuck spacing of the testing machine to 100mm±0.5mm, the stretching rate not exceeding 20mm / min, and the test temperature to 18-25℃; the test conditions for the two-way strain are as follows: load 10-400MPa, electric pulse drive, and record the change of the two-way strain value with the number of cycles.

[0034] Table 2 Heat treatment conditions of examples and comparative examples

[0035] Combining Table 2, Table 3 and Figure 1 As shown in the figure, the martensitic phase transition temperature of the NiTiHfNb high temperature shape memory alloy prepared by the present invention can reach 105-120°C. The reason is that the short rod-shaped or spherical β-Nb phase in nano form, which accounts for 30% of the area in the alloy, significantly increases the phase transition temperature of the alloy; although Comparative Example 2 can also obtain a high phase transition temperature, due to the presence of metal oxidation in its microscopic composition, it cannot maintain stability during the 10-cycle double-pass effect test. Figure 2 and Figure 3 As shown, the short rod-shaped or spherical β-Nb phase obtained by heat treatment in Example 1 makes the NiTiHfNb high temperature shape memory alloy have a wide phase transformation strain range, and the interface effect between the short rod-shaped or spherical β-Nb phase in nanoform and the matrix NiTiHf (Nb) phase is conducive to the storage of prestress, and the obtained NiTiHfNb high temperature shape memory alloy can maintain a highly stable two-way strain value within 10 cycles.

[0036] Table 3 Martensitic transformation temperature of the products of the embodiments and comparative examples

[0037] In summary, the NiTiHfNb high-temperature shape memory alloy prepared in the present invention can be stably used in high-temperature working scenarios, such as aerospace, deep space exploration, solar cell arrays, oil mine detection and fire alarm devices.

[0038] Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. A person with ordinary knowledge in the technical field to which the present invention belongs may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be determined by the definition of the claims.

Claims

1. A high temperature shape memory alloy with two-way effect, characterized in that: The high temperature shape memory alloy is NiTiHfNb high temperature shape memory alloy, and the chemical formula is: (Ni a Ti 100-a-b Hf b ) 100-c Nb c , wherein the value range of a is 45-49.9, the value range of b is 15.1-20, and the value range of c is 5-14.9; the NiTiHfNb high temperature shape memory alloy is microscopically composed of a matrix NiTiHf(Nb) phase and a short rod-shaped or spherical β-Nb phase, and the β-Nb phase is dispersed in the matrix NiTiHf(Nb) phase.

2. The high temperature shape memory alloy with two-way effect according to claim 1, characterized in that: The chemical formula of the NiTiHfNb high temperature shape memory alloy is: 49.5 Ti 35 Hf 15.5 ) 88 Nb 12 .

3. The high temperature shape memory alloy with two-way effect according to claim 1, characterized in that: The NiTiHfNb high temperature shape memory alloy is made by weighing raw materials according to atomic percentage, and sequentially undergoing smelting, hot forging, hot rolling or cold rolling, drawing, and heat treatment. The heat treatment temperature is 400-900 o C, time 10min-120h.

4. A method for preparing a high temperature shape memory alloy with a two-way effect as claimed in any one of claims 1 to 3, characterized in that: The following steps are involved: 1) According to chemical composition (Ni a Ti 100-a-b Hf b ) 100-c Nb c Weigh Ni, Ti, Hf and Nb as raw materials respectively, wherein the value range of a is 45-49.9, the value range of b is 15.1-20, and the value range of c is 5-14.9; 2) smelting the raw materials to obtain a NiTiHfNb alloy ingot; 3) hot forging the NiTiHfNb alloy ingot to obtain a hot forged NiTiHfNb alloy material; 4) hot rolling or cold rolling the hot forged NiTiHfNb alloy ingot to obtain a hot rolled or cold rolled NiTiHfNb alloy material; 5) drawing the hot-rolled or cold-rolled NiTiHfNb alloy ingot to obtain a drawn NiTiHfNb alloy wire; 6) The drawn NiTiHfNb alloy wire is heat treated to obtain a NiTiHfNb high temperature shape memory alloy; wherein the process parameters of the heat treatment are: a heat treatment temperature of 400-900° C. and a heat treatment time of 10 min-120 h.

5. The method for preparing a high temperature shape memory alloy with a two-way effect according to claim 4, characterized in that: In the NiTiHfNb alloy ingot obtained by smelting in step 2), the β-Nb phase exists in a network form in the matrix NiTiHf(Nb) phase, and the area proportion of the β-Nb phase is 15-45%.

6. The method for preparing a high temperature shape memory alloy having a two-way effect according to claim 4, characterized in that: The network morphology of the β-Nb phase of the NiTiHfNb alloy ingot obtained in step 2) is gradually broken during hot forging, hot rolling or cold rolling, and drawing, and is elongated along the main processing direction.

7. The method for preparing a high temperature shape memory alloy with a two-way effect according to claim 4, characterized in that: In the step 6), the drawn NiTiHfNb alloy wire is transformed into a short rod or spherical shape during the heat treatment process.

8. The method for preparing a high temperature shape memory alloy with a two-way effect according to claim 4, characterized in that: The NiTiHfNb alloy material after hot rolling, cold rolling or drawing is heat treated at a temperature of 750° C. for 18-24 hours.

9. Application of the high temperature shape memory alloy with two-way effect as claimed in any one of claims 1 to 3 in high temperature working scenarios.

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