A diffusion-enhanced (Ti 49 Ni 36 Hf 15 ) 98 X2 cast high-temperature shape memory alloy and preparation method thereof

Abstract

The present invention relates to the technical field of shape memory alloys, and in particular to a dispersion strengthened (Ti 49 Ni 36 Hf 15 ) 98 X2 cast high temperature shape memory alloy and its preparation method. The present invention provides (Ti 49 Ni 36 Hf 15 ) 98 The X2 cast high-temperature memory alloy has the following chemical composition, measured in atomic percentage: Ti 48.02%, Ni 35.28%, Hf 14.70%, and X 2%, where X is one of Te, Ge, Bi, and Sb. The alloy is prepared by placing Ti, Ni, Hf, and X raw materials in a vacuum arc melting furnace and repeatedly melting them to produce an alloy ingot. A dispersed strengthening phase precipitates in the cast memory alloy, combining a high phase transition temperature with excellent mechanical properties. The preparation process of the cast memory alloy is very simple. The alloy only requires arc melting, eliminating the need for heat treatments such as solutionizing, aging, homogenizing, and quenching. It also eliminates the need for mechanical processing such as rolling, drawing, and training. The alloy is easy to operate and has excellent application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of alloy materials and their preparation, and specifically relates to a dispersion-strengthened (Ti 49 Ni 36 Hf 15 ) 98 X2 cast high-temperature shape memory alloy and preparation method thereof. Background Art

[0002] High-temperature shape memory alloys refer to shape memory alloys with a martensitic phase transition temperature above 373K (100°C). Among the high-temperature shape memory alloys reported so far, Ti-Ni-Hf alloys have broad application prospects in the fields of aircraft, automobile engines, energy engineering, power generation systems, etc. due to their low cost and good memory properties. However, when the Hf content is high, the fracture strength and plasticity of this type of alloy decrease, the temperature hysteresis increases, and the recoverable strain becomes smaller. In order to overcome the shortcomings of its poor mechanical properties, researchers have adopted alloying treatment, thermomechanical treatment, aging treatment, powder metallurgy, additive manufacturing and other methods. Among them, the alloying treatment method is convenient and effective and has received widespread attention from researchers. Commonly used alloying treatment elements for Ti-Ni-Hf alloys include Zr, Nb, Ta, Y, Sc, Ag, Sn, Al, Cu, Pd, etc. The addition of these elements can improve the phase transition temperature and mechanical properties of Ti-Ni-Hf to a certain extent. However, there are still the following problems to be solved:

[0003] (1) The cost of some added elements is too high, such as Pd, Ag, Zr, Ta, etc.

[0004] (2) Most alloys require heat treatments such as solid solution, aging, homogenization, and quenching, or mechanical processing such as rolling, drawing, and training, and the production and processing technology is relatively complicated;

[0005] (3) Some added elements will significantly reduce the phase transition temperature of Ti-Ni-Hf;

[0006] (4) Some added elements will reduce the mechanical properties of Ti-Ni-Hf;

[0007] (5) Some added elements have high melting points and are refractory metals, such as Zr (1855°C), Nb (2468°C), Ta (3017°C), and Y (1522°C). The smelting process requires more energy.

[0008] In summary, the existing Ti-Ni-Hf high-temperature shape memory alloys still have various problems to be solved. On the one hand, the preparation process needs to be further simplified, and on the other hand, more optimized alloying elements need to be developed to adjust their mechanical properties. Summary of the Invention

[0009] In view of the problems existing in the prior art, the present invention provides a dispersion-strengthened (Ti 49 Ni 36 Hf 15 ) 98 X2 cast high-temperature shape memory alloy and its preparation method use the latest alloying elements to precipitate nano- or micron-sized dispersion strengthening phases in the cast structure. While ensuring the high phase transition temperature of Ti-Ni-Hf alloys, it improves mechanical properties and reduces alloy costs. Moreover, it only uses the simplest melting and casting method, has good comprehensive performance, and has both high phase transition temperature and good mechanical properties within a special composition range.

[0010] In order to achieve the above object, the present invention adopts the following technical solutions:

[0011] A diffusion-enhanced (Ti 49 Ni 36 Hf 15 ) 98 The invention relates to an X2 cast high-temperature shape memory alloy, wherein the alloy comprises the following chemical components in atomic percentage: Ti 48-50%, Ni 35-37%, Hf 14-16%, and X 0-2%, wherein the alloy element X is one of Te, Ge, Bi, and Sb.

[0012] Preferably, the alloy comprises the following chemical composition in atomic percentage: Ti 48.02%, Ni 35.28%, Hf 14.70%, X 2%, and the alloying element X is one of Te, Ge, Bi, and Sb.

[0013] A diffusion-enhanced (Ti 49 Ni 36 Hf 15 ) 98 X2 cast high-temperature shape memory alloy and preparation method thereof, the method comprises the following preparation steps: raw materials Ti, Ni, Hf, X are mixed according to atomic percentage, placed in a vacuum arc melting furnace, vacuumed and filled with argon to prevent oxidation during the alloy melting process, each pass is kept in a molten state for more than 60 seconds and repeatedly melted for more than 5 times to make the alloy components uniformly mixed, and obtain dispersion-strengthened (Ti 49 Ni 36 Hf 15 ) 98 X2 cast high temperature shape memory alloy.

[0014] Preferably, in the preparation step, the vacuum degree of the vacuum arc melting furnace is less than 10 -3 Pa, melting current is 180-310A.

[0015] Preferably, in the preparation step, after argon is filled, the pressure in the smelting furnace is -0.04-0.06 MPa, an arc is struck, and the current is increased to 250-300 A.

[0016] Further preferably, in the step 2), when X=Te, the smelting current is 210-270A, Ti and Ni are placed at the bottom of the crucible, Hf is placed in the middle layer, Te is placed on the upper layer of the raw materials, and the cast (Ti 49 Ni 36 Hf 15 ) 98 The phase transition temperature of Te2 shape memory alloy is 199.2-245.8℃ and it has a compressive strength of 1498.6MPa.

[0017] Further preferably, in the step 2), when X=Ge, the smelting current is 250-310A, Ti and Ni are placed at the bottom of the crucible, Hf is placed on the upper layer, Ge is placed in the middle layer of the raw materials, and the cast (Ti 49 Ni 36 Hf 15 ) 98 The phase transition temperature of Ge2 shape memory alloy is 170.2-225.7℃ and it has a compressive strength of 1523.2MPa.

[0018] Further preferably, in the step 2), when X=Sb, the smelting current is 230-290A, Ti and Ni are placed at the bottom of the crucible, Hf is placed in the middle layer, and Sb is placed on the upper layer of the raw materials. 49 Ni 36 Hf 15 ) 98 The phase transition temperature of Sb2 memory alloy is 191.3-238.1℃ and it has a compressive strength of 1399.4MPa.

[0019] Further preferably, in the step 2), when X=Bi, the smelting current is 180-240A, Ti and Ni are placed on the bottom of the crucible, Hf is placed in the middle layer, and Bi is placed on the upper layer of the raw materials. 49 Ni 36 Hf 15 ) 98 The phase transition temperature of Bi2 shape memory alloy is 208.9-252.4℃ and it has a compressive strength of 1463.6MPa.

[0020] Further preferably, in the step 2), before each smelting of the alloy, pure Ti metal is first smelted and kept in liquid state for 1-2 minutes to consume the residual oxygen in the furnace.

[0021] Preferably, in the preparation step, the dispersion strengthened (Ti 49 Ni36 Hf 15 ) 98 X2 cast high-temperature shape memory alloy only needs to be arc melted, without the need for heat treatment such as solid solution, aging, homogenization, quenching, etc., nor does it require mechanical processing such as rolling, drawing, and training.

[0022] The present invention has the following beneficial effects:

[0023] 1) The present invention selects the novel alloying elements Te, Ge, Sb, and Bi to alloy the Ti-Ni-Hf alloy. Because the alloying elements of the present invention have low solubility in the base alloy, all four elements form fine, nano- or micron-sized dispersion-strengthened phases within the alloy. This improves the mechanical properties of the Ti-Ni-Hf high-temperature shape memory alloy while maintaining a relatively high phase transition temperature.

[0024] 2) The present invention offers a convenient preparation process. The alloy only needs to be arc-melted, and the cast alloy can achieve both excellent mechanical properties and a high phase transition temperature. No heat treatments such as solution treatment, aging, homogenization, and quenching are required, nor are any mechanical processing such as rolling, drawing, or annealing necessary.

[0025] 3) The alloy of the present invention is easy to melt and saves energy. Because the alloying elements of the invention have low melting points, the melting points of Bi, Te, Sb, and Ge are 271°C, 452°C, 630°C, and 937°C, respectively, which are much lower than the melting points of common alloying elements such as Zr (1855°C), Nb (2468°C), Ta (3017°C), and Y (1522°C) used in Ti-Ni-Hf alloys. Therefore, the cast shape memory alloy of the present invention is easy to melt, and the melting current is low and the duration is short, thus saving energy.

[0026] 4) The present invention has low cost. 49 Ni 36 Hf 15 ) 98 Based on X2 alloy, the composition and properties of the alloy are optimized by changing the X element to Te, Ge, Sb, Bi, etc. No precious metals are added. Compared with the common alloying elements used for Ti-Ni-Hf, the alloy cost is lower. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Microstructures of the alloys of Examples 1, 2, 3, and 4 of the present invention and Comparative Examples 1, 2, 3, 4, and 5;

[0028] Figure 2 Phase transition temperatures of alloy 5 prepared in Examples 1, 2, 3, and 4 of the present invention and Comparative Example 1;

[0029] Figure 3 Compression curves of alloy 5 prepared in Examples 1, 2, 3, and 4 of the present invention and Comparative Example 1;

[0030] Figure 4 Memory properties of alloy 5 prepared in Examples 1, 2, 3, 4 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0031] The present invention will be further described below with reference to the accompanying drawings.

[0032] Example 1

[0033] High-purity metal Ti, Ni, Hf, and Te were used as raw materials. After being cleaned with alcohol, the alloy 1 was prepared according to the atomic ratio of 48.02% Ti, 35.28% Ni, 14.70% Hf, and 2% Te. The raw materials were placed in a vacuum arc furnace and evacuated to 1×10 -3 Pa, then fill with argon to -0.05MPa and then strike the arc, control the melting current at 210-270A, and place Te on the upper layer during melting. Keep the alloy in a molten state for more than 60 seconds to ensure that all metals are completely melted together. Use a robot to turn the obtained alloy ingot over, and then repeatedly melt it 5 times to make the raw material composition uniform and obtain dispersion strengthened (Ti 49 Ni 36 Hf 15 ) 98 Te2 as-cast high-temperature shape memory alloy.

[0034] The microstructure of the alloy 1 is as follows: Figure 1 As shown in (a), fine dispersion strengthening phases of nanometer and micrometer scale appear in the structure. The phase transformation temperature of the obtained alloy 1 is as follows: Figure 2 As shown in (a), the phase transition peak temperature is 199.6-245.8℃, which belongs to high temperature shape memory alloy. The compression curve of alloy 1 is as follows Figure 3 As shown, the compressive strength is 1498.6MPa. The memory performance test of the obtained alloy 1 is as follows Figure 4 As shown in (a), 4% pre-strain can be fully recovered.

[0035] Example 2

[0036] High-purity metal Ti, Ni, Hf, and Ge were used as raw materials. After being cleaned with alcohol, the alloy 2 was prepared according to the atomic ratio of 48.02% Ti, 35.28% Ni, 14.70% Hf, and 2% Ge. The raw materials were placed in a vacuum arc furnace and evacuated to 1×10 -3Pa, then fill with argon to -0.05MPa and then strike the arc, control the melting current at 250-310A, and place Ge in the middle layer during melting. Keep the alloy in a molten state for more than 60 seconds to ensure that all metals are completely melted together. Use a robot to turn the obtained alloy ingot over, and then repeatedly melt it 5 times to make the raw material composition uniform and obtain dispersion strengthened (Ti 49 Ni 36 Hf 15 ) 98 Ge2 cast high temperature shape memory alloy.

[0037] The microstructure of alloy 2 is as follows: Figure 1 As shown in (b), a micron-sized fine dispersion strengthening phase appears in the structure. The phase transition temperature of the obtained alloy 2 is as follows Figure 2 As shown in (b), the phase transition peak temperature is 170.2-225.7℃, which belongs to high temperature shape memory alloy. The compression curve of alloy 2 is as follows Figure 3 As shown, the compressive strength is 1399.4MPa. The memory performance test of the obtained alloy 2 is as follows Figure 4 As shown in (b), 4% pre-strain can recover 3.9%.

[0038] Example 3

[0039] High-purity metal Ti, Ni, Hf, and Sb were used as raw materials. After being cleaned with alcohol, the alloy 3 was prepared according to the atomic ratio of 48.02% Ti, 35.28% Ni, 14.70% Hf, and 2% Sb. The raw materials were placed in a vacuum arc furnace and evacuated to 1×10 -3 Pa, then fill with argon to -0.05MPa and then strike the arc, control the melting current at 230-290A, and place Sb on the upper layer during melting. Keep the alloy in a molten state for more than 60 seconds to ensure that all metals are completely melted together. Use a robot to turn the obtained alloy ingot over, and then repeatedly melt it 5 times to make the raw material composition uniform and obtain dispersion strengthened (Ti 49 Ni 36 Hf 15 ) 98 Sb2 cast high temperature shape memory alloy.

[0040] The microstructure of alloy 3 is as follows: Figure 1 As shown in (c), micron-sized fine dispersion strengthening phases appear in the structure. The phase transition temperature of the obtained alloy 3 is as follows: Figure 2 As shown in (c), the phase transition peak temperature is 191.3-238.1℃, which belongs to high temperature shape memory alloy. The compression curve of alloy 3 is as follows Figure 3 As shown in Figure 2, the compressive strength is 1463.6 MPa. The memory performance test of the obtained alloy 3 is as follows: Figure 4 As shown in (c), 4% pre-strain can be fully recovered.

[0041] Example 4

[0042] High-purity metal Ti, Ni, Hf, and Bi were used as raw materials. After being cleaned with alcohol, the alloy 4 was prepared according to the atomic ratio of 48.02% Ti, 35.28% Ni, 14.70% Hf, and 2% Bi. The raw materials were placed in a vacuum arc furnace and evacuated to 1×10 -3 Pa, then fill with argon to -0.05MPa and then strike the arc, control the melting current at 180-240A, and place Bi on the upper layer during melting. Keep the alloy in a molten state for more than 60 seconds to ensure that all metals are completely melted together. Use a robot to turn the obtained alloy ingot over, and then repeat the melting 5 times to make the raw material composition uniform and obtain dispersion strengthened (Ti 49 Ni 36 Hf 15 ) 98 Bi2 cast high temperature shape memory alloy.

[0043] The microstructure of alloy 4 is as follows: Figure 1 As shown in (d), micron-sized fine dispersion strengthening phases appear in the structure. The phase transition temperature of the obtained alloy 4 is as follows: Figure 2 As shown in (d), the phase transition peak temperature is 208.9-252.4℃, which belongs to high temperature shape memory alloy. The compression curve of alloy 4 is as follows Figure 3 As shown, the compressive strength is 1523.2MPa. The memory performance test of the obtained alloy 4 is as follows Figure 4 As shown in (d), 4% pre-strain can be fully recovered.

[0044] Comparative Example 1

[0045] High-purity metal Ti, Ni, and Hf are used as raw materials. After being cleaned with alcohol, the alloy 5 is prepared according to the atomic ratio of 46% Ti, 39% Ni, and 15.0% Hf. The raw materials are placed in a vacuum arc furnace and evacuated to 1×10 -3 Pa, then fill with argon to -0.05MPa and then strike the arc, control the melting current at 260-320A. Keep the alloy in a molten state for more than 60 seconds to ensure that all metals are completely melted together. Use a robot to turn the obtained alloy ingot over, and then repeat the melting 5 times to make the raw material composition uniform, and obtain cast Ti 49 Ni 36 Hf 15 Shape memory alloy. The microstructure of alloy 5 is as follows Figure 1 As shown in (e), there is no fine dispersion strengthening phase in the structure. The phase transformation temperature of the obtained alloy 5 is as follows Figure 2 As shown in (e), the phase transition peak temperature is 213.0-249.9℃, which belongs to high temperature shape memory alloy. The compression curve of alloy 5 is as follows Figure 3As shown in Figure 2, the compressive strength is only 484.6MPa, which is low and cracks occurred during the compression process. The memory performance test of the obtained alloy 5 is shown in Figure 2. Figure 4 As shown in (e), 4% pre-strain can recover 3.8%.

[0046] Comparative Example 2

[0047] High-purity metal Ti, Ni, Hf, and Co were used as raw materials. After being cleaned with alcohol, the alloy 6 was prepared according to the atomic ratio of 48.02% Ti, 35.28% Ni, 14.70% Hf, and 2% Co. The raw materials were placed in a vacuum arc furnace and evacuated to 1×10 -3 Pa, then fill with argon to -0.05MPa and then strike the arc, control the melting current at 290-350A. Keep the alloy in a molten state for more than 60 seconds to ensure that all metals are completely melted together. Use a robot to turn the alloy ingot over, and then repeat the melting 5 times to make the raw material composition uniform, and obtain the cast state (Ti 49 Ni 36 Hf 15 ) 98 Co2 shape memory alloy. Figure 1 As shown in (f), the microstructure of Alloy 6 lacks fine dispersion-strengthened phases. The resulting Alloy 6 exhibits a phase transformation peak temperature of 125.2-182.9°C, making it a high-temperature shape memory alloy. The resulting Alloy 6 exhibits a compressive strength of only 473.9 MPa.

[0048] Comparative Example 3

[0049] High-purity metal Ti, Ni, Hf, and Cr were used as raw materials. After being cleaned with alcohol, the alloy 7 was prepared according to the atomic ratio of 48.02% Ti, 35.28% Ni, 14.70% Hf, and 2% Cr. The raw materials were placed in a vacuum arc furnace and evacuated to 1×10 -3 Pa, then fill with argon to -0.05MPa and then strike the arc, control the melting current at 280-340A. Keep the alloy in a molten state for more than 60 seconds to ensure that all metals are completely melted together. Use a robot to turn the obtained alloy ingot over, and then repeat the melting 5 times to make the raw material composition uniform, and obtain the cast state (Ti 49 Ni 36 Hf 15 ) 98 Cr2 shape memory alloy. The microstructure of the obtained alloy 7 does not contain fine dispersion strengthening phases. Figure 1 As shown in (g), the phase transformation peak temperature of the obtained alloy 7 is 90.2-132.0°C, which does not belong to a high-temperature shape memory alloy. The compressive strength of the obtained alloy 7 is only 447.85 MPa.

[0050] Comparative Example 4

[0051] High-purity metal Ti, Ni, Hf, and Sn are used as raw materials, and after being cleaned with alcohol, the atomic ratio of 48.02% Ti, 35.28% Ni, 14.70% Hf, and 2% Sn is prepared to form Alloy 8. The preparation method of Alloy 8 in this comparative example is the same as that of Example 4.

[0052] The microstructure of the obtained alloy 8 is as follows Figure 1 As shown in (h), there are no fine dispersion-strengthened phases in the microstructure. The resulting Alloy 8 has a phase transformation peak temperature of 207.5-253.2°C, making it a high-temperature shape memory alloy. The resulting Alloy 8 has a compressive strength of 1130.2 MPa.

[0053] Comparative Example 5

[0054] High-purity metal Ti, Ni, Hf, and Mn are used as raw materials, and after washing with alcohol, the atomic ratio of 48.02% Ti, 35.28% Ni, 14.70% Hf, and 2% Mn is prepared to form Alloy 9. The preparation method of Alloy 9 in this comparative example is the same as that of Example 2.

[0055] The microstructure of the obtained alloy 9 is as follows Figure 1 As shown in (i), there are no fine dispersion-strengthened phases in the microstructure. The resulting Alloy 9 has an austenite transformation peak temperature of 135.6°C and a martensite transformation temperature below 50°C, making it not a high-temperature shape memory alloy. The resulting Alloy 9 has a compressive strength of only 900.1 MPa.

[0056] Table 1 Phase transition temperature and strength of alloys of Examples 1-4 and Comparative Examples 1-5

[0057]

[0058] From the data in Table 1, it can be seen that the dispersion strengthened (Ti 49 Ni 36 Hf 15 ) 98 X2 cast high-temperature shape memory alloy combines a high phase transition temperature with excellent mechanical properties. Its martensite transition temperature reaches 170.2-208.9°C, its austenite transition temperature reaches 225.7-252.4°C, and it also has a compressive strength of 1363.6-1523.2MPa.

[0059] The above embodiments are merely preferred technical solutions of the present invention and should not be construed as limiting the present invention. The embodiments and features in the embodiments of this application may be arbitrarily combined with each other unless they conflict. The scope of protection of the present invention shall be the technical solutions described in the claims, including equivalent alternatives to the technical features of the technical solutions described in the claims. Equivalent alternatives and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A diffusion-enhanced (Ti 49 Ni 36 Hf 15 ) 98 X2 cast high temperature shape memory alloy, characterized in that The alloy is composed of the following chemical components in atomic percentage: Ti 48-50%, Ni 35-37%, Hf 14-16%, X 2%, where the alloy element X is one of Te, Ge, Bi, and Sb. The dispersion-strengthened (Ti 49 Ni 36 Hf 15 ) 98 X2 cast high temperature shape memory alloy.

2. According to claim 1, a dispersion-strengthened (Ti 49 Ni 36 Hf 15 ) 98 X2 cast high temperature shape memory alloy, the alloy consisting of the following chemical compositions in atomic percentage: Ti 48.02%, Ni 35.28%, Hf 14.70%, X 2%, alloy element X is one of Te, Ge, Bi, and Sb.

3. A dispersion-strengthened (Ti according to claim 1 49 Ni 36 Hf 15 ) 98 X2 cast high temperature shape memory alloy, characterized in that The dispersion strengthened (Ti 49 Ni 36 Hf 15 ) 98 The martensite transformation temperature of the X2 cast high-temperature shape memory alloy reaches 170.2-208.9°C, the austenite transformation temperature reaches 225.7-252.4°C, and it also has a compressive strength of 1363.6-1523.2 MPa.

4. A dispersion-strengthened (Ti) according to any one of claims 1 to 3 49 Ni 36 Hf 15 ) 98 A method for manufacturing an X2 as-cast high-temperature shape memory alloy, characterized in that: The alloy manufacturing method comprises the following preparation steps: The raw materials Ti, Ni, Hf, and X are mixed according to atomic percentages and placed in a vacuum arc melting furnace. After evacuation, argon is filled in to prevent oxidation during the alloy melting process. Melting in the molten state to mix the alloy components evenly, that is, dispersion strengthening (Ti 49 Ni 36 Hf 15 ) 98 X2 cast high temperature shape memory alloy.

5. The manufacturing method according to claim 4, characterized in that In the method, the vacuum degree of the vacuum arc melting furnace is less than 10 -3 Pa, melting current 180-310 A, each pass in the molten state lasts for more than 60 seconds.

6. The manufacturing method according to claim 4, characterized in that The molten state is maintained for more than 60 seconds and the smelting is repeated for more than 5 times; after filling with argon gas, the pressure in the smelting furnace is (-0.04) ~ (-0.06) MPa.

7. The manufacturing method according to claim 4, characterized in that When X = Te, the melting current is 210-270A, Ti and Ni are placed at the bottom of the crucible, Hf is placed in the middle layer, and Te is placed on the upper layer of the raw materials; When X = Ge, the melting current is 250-310A. During melting, Ti and Ni are placed at the bottom of the crucible, Hf is placed on the upper layer, and Ge is placed in the middle layer of the raw materials.

8. The manufacturing method according to claim 4, characterized in that When X = Sb, the smelting current is 230-290A. During smelting, Ti and Ni are placed on the bottom of the crucible, Hf is placed in the middle layer, and Sb is placed on the upper layer of the raw materials.

9. The manufacturing method according to claim 4, characterized in that When X = Bi, the smelting current is 180-240A. During smelting, Ti and Ni are placed on the bottom of the crucible, Hf is placed in the middle layer, and Bi is placed on the upper layer of the raw materials.

10. The manufacturing method according to claim 4, characterized in that: Before melting the alloy each time, melt pure Ti metal first and keep it in liquid state for 1-2 minutes to consume the residual oxygen in the furnace.

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