A high-entropy alloy for low temperature and a preparation method and application thereof

Abstract

The application provides a high-entropy alloy for low temperature, a preparation method and application thereof. The high-entropy alloy comprises a base alloy, an N element and an auxiliary element; the base alloy is Co a Cr b Fe c Ni d Mn e The auxiliary element is Ti and / or Ta; the high-entropy alloy comprises any one of (Ni, Co, Fe)3Ti precipitated phases, (Ni, Co, Fe)3Ta precipitated phases or (Ni, Co, Fe)3(Ti, Ta) precipitated phases or a combination of at least two; and the average grain size of the high-entropy alloy is 0.1-15 mu m. The preparation method comprises the following steps: melting raw materials of the high-entropy alloy and suction casting into a water-cooled copper mold to obtain a cast high-entropy alloy material, heat treating and cold rolling to obtain a high-entropy alloy plate, and cold rolling with a reduction of 75-90%; and annealing the high-entropy alloy plate to obtain the high-entropy alloy for low temperature. The application can solve the technical bottleneck that the yield strength of the existing low-temperature structural material is low in a low-temperature environment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-entropy alloys, and particularly relates to a high-entropy alloy for low temperature, a preparation method and application thereof. BACKGROUND

[0002] The austenitic stainless steel material has excellent low-temperature yield strength, plasticity, non-magneticity and weldability, and the fracture toughness thereof does not decrease significantly with the decrease of temperature, and can be used as a low-temperature structural material of a large high-field superconducting magnet such as a magnetic confinement nuclear fusion, an accelerator and an MRI. The austenitic stainless steel has been used as a sheath material of a cable-in-conduit conductor (CICC) and a longitudinal field TF coil box structural material of a superconducting high-field magnet of a magnetic confinement nuclear fusion. The next generation of magnetic confinement nuclear fusion requires that the structural material has a liquid helium temperature yield strength greater than 1300 MPa.

[0003] In recent years, a new type of high-entropy alloy has become a potential high-performance low-temperature structural material due to excellent low-temperature toughness and yield strength ratio. In particular, the high-entropy alloy with an FCC (face-centered cubic) structure has the characteristics of being more tough at a lower temperature because of the generation of nanotwins during low-temperature deformation to prevent local destructive deformation, and is therefore recognized as an ideal structural material below 20K. At present, the research on the high-entropy alloy with an FCC structure is based on fine-grain strengthening treatment or precipitation strengthening mechanism, and the principle is to improve the strength of the alloy by hindering the movement of dislocations. However, in the extremely low temperature region, due to the decrease of atomic activity and the difficulty of dislocation movement and proliferation, the main deformation mechanism of the alloy will change to twinning mechanism, which will inevitably greatly reduce the effect of the above two strengthening measures.

[0004] Therefore, it is urgent to develop a high-N precipitation strengthened high-strength and tough low-temperature high-entropy alloy material and a preparation technology thereof for the 4K temperature region. SUMMARY

[0005] In view of the deficiencies in the prior art, the purpose of the present application is to provide a high-entropy alloy for low temperature, a preparation method and application thereof, and a high-N precipitation strengthened high-strength and tough low-temperature high-entropy alloy material and a preparation method thereof for the 4K temperature region are developed, and the performance is expected to meet the demand of the low-temperature mechanical properties of the conductor sheath material for the CFTER engineering reactor.

[0006] To achieve this purpose, the technical scheme adopted by the present application is as follows:

[0007] In a first aspect, the present application provides a high-entropy alloy for low temperature, which comprises a base alloy, an N element and an auxiliary element. The base alloy is Co a Cr b Fe c Ni d Mn eHigh-entropy alloy. The auxiliary element is Ti and / or Ta. The high-entropy alloy has a precipitate phase, the precipitate phase includes any one of (Ni, Co, Fe)3Ti precipitate phase, (Ni, Co, Fe)3Ta precipitate phase or (Ni, Co, Fe)3(Ti,Ta) precipitate phase or a combination of at least two, and the average grain size of the high-entropy alloy is 0.1-15 μm.

[0008] The present application is a face-centered cubic structure Co a Cr b Fe c Ni d Mn e The high-entropy alloy is the matrix, which provides sufficient low-temperature toughness and plasticity; at the same time, by adding N element and Ti, Ta and the like, a high N matrix and nano γ' precipitate phase are formed, and through the synergistic effect of matrix strengthening, solid solution strengthening and grain boundary strengthening, sufficient low-temperature strength is provided.

[0009] The present application preferably contains Ti and Ta as auxiliary elements, wherein the Ta element can effectively promote the precipitation of the strengthening phase and improve the strengthening effect, and the Ti can effectively reduce the generation of hard and brittle intermetallic compounds and improve the low-temperature toughness.

[0010] The average grain size of the high-entropy alloy is 0.1-15 μm, for example, it can be 0.1 μm, 0.2 μm, 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 3 μm, 3.2 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 6 μm, 7 μm, 8 μm, 10 μm, 12 μm or 15 μm, etc., preferably 0.5-1.5 μm.

[0011] Preferably, the high-entropy alloy does not contain BCC phase and / or hard and brittle intermetallic compounds in the organizational structure.

[0012] Preferably, the Co a Cr b Fe c Ni d Mn eIn the high-entropy alloy, a, b, c, d, and e are (0.001-1.5):(0.9-1.1):1:(0.9-1.1):(0.001-1), wherein a, b, c, d, and e are the number of atoms. For example, a can be 0.001, 0.1, 0.3, 0.5, 0.6, 0.8, 1, 1.1, 1.3, or 1.5, but is not limited to the listed values, and other values not listed in the range are also applicable. For example, b can be 0.9, 0.93, 0.95, 0.97, 0.99, 1.02, 1.04, 1.06, 1.08, or 1.1, but is not limited to the listed values, and other values not listed in the range are also applicable. For example, d can be 0.9, 0.93, 0.95, 0.97, 0.99, 1.02, 1.04, 1.06, 1.08, or 1.1, but is not limited to the listed values, and other values not listed in the range are also applicable. For example, e can be 0.001, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 1, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0013] Preferably, the average grain size of the high-entropy alloy is 0.5-5 μm, for example, 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 3 μm, 3.2 μm, 3.5 μm, 4 μm, 4.5 μm, or 5 μm, preferably 0.5-1.5 μm.

[0014] The average grain size of the high-entropy alloy in the present application is small, which can effectively hinder the movement of dislocations and better improve the low-temperature strength.

[0015] Preferably, the size of the precipitated phase is in the range of 10-50 nm, for example, 10 nm, 12 nm, 14 nm, 15 nm, 18 nm, 20 nm, 22 nm, 25 nm, 28 nm, 30 nm, 32 nm, 35 nm, 38 nm, 40 nm, 45 nm, or 50 nm, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0016] The size of the precipitated phase is controlled in the above range, which can significantly improve the low-temperature performance of the high-entropy alloy.

[0017] Preferably, the mass percentage of N in the high-entropy alloy is 0.02-0.07 wt%, for example, 0.02 wt%, 0.03 wt%, 0.04 wt%, 0.05 wt%, 0.06 wt%, or 0.07 wt%, but not limited to the listed values, and other values not listed in the range are also applicable.

[0018] The present application preferably controls the content of N within the above range, which can avoid the decrease in low-temperature strength and toughness caused by the precipitation of a large amount of nitrides.

[0019] Preferably, the molar ratio of the sum of the auxiliary elements to the elements in the base alloy in the high-entropy alloy is (0.001-0.2):1, for example, 0.001:1, 0.024:1, 0.046:1, 0.068:1, 0.09:1, 0.112:1, 0.134:1, 0.156:1, 0.178:1, or 0.2:1, but not limited to the listed values, and other values not listed in the range are also applicable.

[0020] It is worth noting that both Ta and Ti are extremely strong body-centered cubic structure stabilizing elements, and excessive addition will cause the generation of BCC phase and hard brittle intermetallic compounds, resulting in low-temperature strength and toughness of the material, and a low amount of auxiliary elements will not be able to achieve the strengthening effect.

[0021] Preferably, the molar ratio of Ta and Ti in the high-entropy alloy is (0.05-0.15):1, for example, 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.1:1, 0.11:1, 0.12:1, 0.13:1, 0.14:1, or 0.15:1, but not limited to the listed values, and other values not listed in the range are also applicable.

[0022] The present application preferably controls the molar ratio of Ta and Ti within the above range, which can further improve the low-temperature performance of the high-entropy alloy.

[0023] Preferably, the yield strength of the high-entropy alloy at 77K is greater than 1.3 GPa, for example, 1.31 GPa, 1.34 GPa, 1.36 GPa, 1.38 GPa, 1.4 GPa, 1.42 GPa, 1.44 GPa, 1.46 GPa, 1.48 GPa, or 1.5 GPa, but not limited to the listed values, and other values not listed in the range are also applicable; the elongation is greater than 20%, for example, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 32%, 33%, 35%, 38%, 40%, etc.

[0024] Preferably, the high-entropy alloy has a tensile strength greater than 1.6 GPa at 77 K, for example, it can be 1.61 GPa, 1.66 GPa, 1.7 GPa, 1.74 GPa, 1.79 GPa, 1.83 GPa, 1.87 GPa, 1.92 GPa, 1.96 GPa or 2.0 GPa, etc., but not limited to the listed values, other unlisted values within the range are also applicable.

[0025] Preferably, the high-entropy alloy has a yield strength greater than 1.5 GPa at 4.2 K, for example, it can be 1.51 GPa, 1.57 GPa, 1.62 GPa, 1.68 GPa, 1.73 GPa, 1.79 GPa, 1.84 GPa, 1.9 GPa, 1.95 GPa or 2.0 GPa, etc., but not limited to the listed values, other unlisted values within the range are also applicable.

[0026] Preferably, the high-entropy alloy has a tensile strength greater than 1.8 GPa at 4.2 K, for example, it can be 1.81 GPa, 1.86 GPa, 1.9 GPa, 1.94 GPa, 1.99 GPa, 2.03 GPa, 2.07 GPa, 2.12 GPa, 2.16 GPa or 2.2 GPa, etc., but not limited to the listed values, other unlisted values within the range are also applicable.

[0027] In a second aspect, the present application provides a preparation method of the high-entropy alloy for low temperature in the first aspect, the preparation method comprises:

[0028] (1) Melting and suction casting the raw materials of the high-entropy alloy into a water-cooled copper mold to obtain a cast high-entropy alloy material.

[0029] (2) The high-entropy alloy material in step (1) is subjected to heat treatment and cold rolling to obtain a high-entropy alloy plate, wherein the cold rolling reduction is 75-90%.

[0030] (3) The high-entropy alloy plate in step (2) is subjected to annealing treatment to obtain the high-entropy alloy for low temperature.

[0031] In the present application, the cold rolling reduction is 75-90%, generally, the cold rolling temperature is room temperature (10-35℃, in an unheated or cooled state), cold rolling is carried out at this temperature, and the reduction is controlled within the above range, which can generate a large amount of distortion energy in the material, and cooperate with the subsequent annealing treatment, so that recrystallization can be quickly realized, the number of recrystallization nuclei is large, and the growth process is mutually restricted, forming a high-entropy alloy product with small grain size.

[0032] The heat treatment, the cold rolling and the annealing treatment in the present application must be carried out in sequence, wherein the heat treatment is used for homogenization treatment to make the structure and the composition uniform, and the cold rolling and the annealing treatment are used for recrystallization to form a fine matrix and promote the precipitation of precipitates.

[0033] The cold rolling reduction in the present application is 75-90%, for example, can be 75%, 77%, 79%, 80%, 82%, 84%, 85%, 87%, 89% or 90%, etc., but is not limited to the listed values, and other unlisted values in the range are also applicable.

[0034] Preferably, the smelting in step (1) is vacuum arc smelting.

[0035] Preferably, the smelting is repeated at least 5 times, for example, can be 5 times, 6 times, 7 times, 8 times, 9 times, 10 times, 11 times or 12 times, etc.

[0036] The smelting of each alloy raw material is repeated 5 times to ensure the uniformity of the chemical composition and the microstructure, so that each alloy raw material is melted into an alloy liquid in a low-loss and highly uniform mixed state, and then the alloy liquid is naturally cooled in the vacuum smelting furnace to achieve the goal of slow forming.

[0037] Preferably, the smelting is carried out in an argon atmosphere.

[0038] Preferably, the heat treatment in step (2) is carried out in a vacuum environment.

[0039] Preferably, the vacuum degree of the heat treatment is ≤10 -5 Pa, for example, can be 10 -5 Pa, 0.9×10 -5 Pa, 0.8×10 -5 Pa, 0.7×10 -5 Pa, 0.6×10 -5 Pa, 0.5×10 -5 Pa, 0.4×10 -5 Pa, 0.3×10 -5 Pa, 0.2×10 -5 Pa or 0.1×10 -5 Pa, etc.

[0040] Preferably, the temperature of the heat treatment is 600-800℃, for example, can be 600℃, 620℃, 645℃, 660℃, 680℃, 710℃, 730℃, 750℃, 770℃ or 800℃, etc., but is not limited to the listed values, and other unlisted values in the range are also applicable.

[0041] Preferably, the heat treatment time is 6-10h, for example, it can be 6h, 6.5h, 6.9h, 7.4h, 7.8h, 8.3h, 8.7h, 9.2h, 9.6h or 10h, etc., but not limited to the listed values, other values in the range are also applicable.

[0042] The application preferably controls the heat treatment temperature in the above range, which can avoid excessive grain growth, thereby improving the low temperature strength and toughness of the high-entropy alloy.

[0043] Preferably, the annealing temperature in step (3) is 650-750℃, for example, it can be 650℃, 662℃, 673℃, 684℃, 695℃, 706℃, 717℃, 728℃, 739℃ or 750℃, etc., but not limited to the listed values, other values in the range are also applicable.

[0044] The application preferably controls the annealing temperature in the above range, which can improve the precipitation of precipitates, avoid the coarsening of precipitates, and effectively avoid element segregation, thereby improving the microstructure stability and low temperature strength of the high-entropy alloy at low temperature.

[0045] Preferably, the annealing time is 6-10h, for example, it can be 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h or 10h, etc., but not limited to the listed values, other values in the range are also applicable.

[0046] In a third aspect, the application provides a high-entropy alloy for low temperature in the first aspect in aerospace, nuclear fusion or accelerator.

[0047] Compared with the prior art, the application has at least the following beneficial effects:

[0048] (1) The high-entropy alloy for low temperature provided by the application has high tensile strength and yield strength at low temperature, and can be well applied in the fields of aerospace, nuclear fusion or accelerator, etc.

[0049] (2) The preparation method of the high-entropy alloy for low temperature provided by the application combines component selection and process, which can reduce the grain size of the high-entropy alloy, thereby improving the tensile strength and yield strength at low temperature. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1 is the metallographic structure diagram of the high-entropy alloy for low temperature in Example 1 of the application.

[0051] Figure 2 is the TEM diagram of the high-entropy alloy for low temperature in Example 1 of the application. DETAILED DESCRIPTION

[0052] In order to facilitate the understanding of the present application, the present application is illustrated by the following examples. It should be understood by those skilled in the art that the examples are only for the purpose of understanding the present application and should not be regarded as specific limitations of the present application.

[0053] Example 1

[0054] The present example provides a high-entropy alloy for low temperature, which comprises a base alloy, an N element and an auxiliary element; the base alloy is Co a Cr b Fe c Ni d Mn e high-entropy alloy; the atomic ratio of a:b:c:d:e is 1:1:1:1:1; the auxiliary element is Ti and Ta (the molar ratio of Ta and Ti is 0.08:1); the molar ratio of the auxiliary element to the sum of the elements in the base alloy in the high-entropy alloy is 0.054:1, i.e. the high-entropy alloy is CoCrFeNiMnTi 0.25 Ta 0.02 , and wherein the mass percentage of the N element is 0.05wt%.

[0055] The present example also provides a preparation method of the high-entropy alloy for low temperature, which comprises:

[0056] (1) under an argon atmosphere, vacuum arc melting raw materials of the high-entropy alloy (adding chromium nitride to introduce nitrogen element) for at least 10 times and suction casting into a water-cooled copper mold to obtain a cast high-entropy alloy material;

[0057] (2) heat treating the high-entropy alloy material in step (1) at a vacuum degree of ≤10 -5 Pa and 700℃ for 8h, and then cold rolling, wherein the cold rolling reduction is 80% to obtain a high-entropy alloy plate;

[0058] (3) annealing the high-entropy alloy plate in step (2) at 700℃ for 9h to obtain the high-entropy alloy for low temperature.

[0059] The microstructure diagram of the high-entropy alloy obtained by the present example is shown in Figure 1 From Figure 1 it can be seen that the high-entropy alloy prepared in the present example has small grain size; the TEM diagram is shown in Figure 2 From Figure 2 it can be seen that the high-entropy alloy prepared in the present example has nanometer precipitates.

[0060] Example 2

[0061] The present example provides a high-entropy alloy for low temperature, which comprises a base alloy, an N element and an auxiliary element; the base alloy is Coa Cr b Fe c Ni d Mn e high-entropy alloy; the atomic ratio of a:b:c:d:e is 1.2:1:1:1:0.8; the auxiliary elements are Ta and Ti (the molar ratio of Ta and Ti is 0.083:1); the molar ratio of the auxiliary elements in the high-entropy alloy to the sum of the elements in the base alloy is 0.032:1, i.e., the high-entropy alloy is Co 1.2 CrFeNiMn 0.8 Ti 0.15 Ta 0.01 , and the mass percentage of the N element is 0.02wt%.

[0062] The embodiment also provides a preparation method of the low-temperature high-entropy alloy, and the preparation method comprises the following steps:

[0063] (1) under an argon atmosphere, vacuum arc melting raw materials of a high-entropy alloy (adding chromium nitride to introduce a nitrogen element) for at least 10 times, and suction casting into a water-cooled copper mold to obtain a cast high-entropy alloy material;

[0064] (2) the high-entropy alloy material in step (1) is subjected to heat treatment at a vacuum degree of ≤10 -5 Pa and 600℃ for 10h, and then cold rolling, wherein the cold rolling reduction is 75%, to obtain a high-entropy alloy plate;

[0065] (3) the high-entropy alloy plate in step (2) is subjected to annealing treatment at 750℃ for 6h to obtain the low-temperature high-entropy alloy.

[0066] Embodiment 3

[0067] The embodiment provides a low-temperature high-entropy alloy, which comprises a base alloy, an N element and auxiliary elements; the base alloy is Co a Cr b Fe c Ni d Mn e high-entropy alloy; the atomic ratio of a:b:c:d:e is 0.9:1:1:1:0.9; the auxiliary elements are Ta and Ti (the molar ratio of Ta and Ti is 0.15:1); the molar ratio of the auxiliary elements in the high-entropy alloy to the sum of the elements in the base alloy is 0.048:1, i.e., the high-entropy alloy is Co 0.9 CrFeNiMn 0.9 Ti 0.2 Ta 0.0 3, and the mass percentage of the N element is 0.07wt%.

[0068] The embodiment also provides a preparation method of the high-entropy alloy for low temperature, and the preparation method comprises the following steps:

[0069] (1) under an argon atmosphere, vacuum arc melting raw materials of the high-entropy alloy (adding chromium nitride to introduce nitrogen elements) for at least 10 times, and suction casting into a water-cooled copper mold to obtain a cast high-entropy alloy material;

[0070] (2) the high-entropy alloy material in step (1) is heated at 800 DEG C for 6 hours under a vacuum degree of ≤10 -5 Pa, and then cold-rolled, wherein the cold-rolling reduction is 90%, to obtain a high-entropy alloy plate;

[0071] (3) the high-entropy alloy plate in step (2) is annealed at 650 DEG C for 10 hours to obtain the high-entropy alloy for low temperature.

[0072] Embodiment 4

[0073] The embodiment provides a high-entropy alloy for low temperature, which is the same as that in embodiment 1 except that no Ti element is added and the Ti element is replaced by a Ta element.

[0074] Embodiment 5

[0075] The embodiment provides a high-entropy alloy for low temperature, which is the same as that in embodiment 1 except that no Ta element is added and the Ta element is replaced by a Ti element.

[0076] Embodiment 6

[0077] The embodiment provides a high-entropy alloy for low temperature, which is the same as that in embodiment 1 except that the mass percentage content of N element in the high-entropy alloy is 0.1 wt%.

[0078] Embodiment 7

[0079] The embodiment provides a high-entropy alloy for low temperature, which is the same as that in embodiment 1 except that the molar ratio of the sum of auxiliary elements and elements in the base alloy is 0.3:1.

[0080] Embodiment 8

[0081] The embodiment provides a high-entropy alloy for low temperature, which is the same as that in embodiment 1 except that the annealing temperature is 850 DEG C.

[0082] Embodiment 9

[0083] This embodiment provides a high-entropy alloy for low temperature, which is the same as that of embodiment 1 except that the temperature of annealing treatment is 500℃, which is not repeated here.

[0084] Example 10

[0085] This embodiment provides a high-entropy alloy for low temperature, which is the same as that of embodiment 1 except that the temperature of annealing treatment is 800℃, which is not repeated here.

[0086] Comparative Example 1

[0087] This comparative example provides a high-entropy alloy, which is the same as that of embodiment 1 except that no N element is added, which is not repeated here.

[0088] Comparative Example 2

[0089] This comparative example provides a high-entropy alloy, which is the same as that of embodiment 1 except that Ti and Ta elements are all replaced by Al element, which is not repeated here.

[0090] Comparative Example 3

[0091] This comparative example provides a high-entropy alloy, which is the same as that of embodiment 1 except that no Ti and Ta elements are added, which is not repeated here.

[0092] Comparative Example 4

[0093] This comparative example provides a high-entropy alloy, which is the same as that of embodiment 1 except that CrFeNiMn alloy (molar ratio of 1:1:1:1) is used, which is not repeated here.

[0094] Test method: The average grain size of the alloy is tested by scanning electron microscope electron backscatter diffraction technology, the size range of the precipitated phase in the alloy is tested by transmission electron microscopy technology, the tensile strength and yield strength of the alloy at 77K are tested by GB / T 228.3 metal material tensile test part 3: low temperature test method, and the tensile strength and yield strength of the alloy at 4.2K are tested by GBT 228.4-2019 metal material tensile test part 4: liquid helium test method.

[0095] The test results of the above examples and comparative examples are shown in Table 1.

[0096] Table 1

[0097]

[0098] The " / " in Table 1 represents no relevant data or relevant phase. The γ' refers to the presence of at least one of a (Ni, Co, Fe) 3 Ti precipitate phase, a (Ni, Co, Fe) 3 Ta precipitate phase, or a (Ni, Co, Fe) 3 (Ti, Ta) precipitate phase.

[0099] The following points can be seen from Table 1:

[0100] (1) As can be seen from Examples 1-3, the high-entropy alloy for low temperature provided by the application has a tensile strength of 1.65 GPa or more at 77 K, a yield strength of 1.33 GPa or more, a tensile strength of 1.84 GPa or more at 4.2 K, and a yield strength of 1.56 GPa or more, which has a broad application prospect in aerospace, nuclear fusion or accelerators.

[0101] (2) As can be seen from Examples 1 and 4-5, in Example 1, Ti and Ta are used as auxiliary elements, not only the yield strength at 77 K and 4.2 K is significantly higher, but also the elongation at break at 77 K is 32%. In Example 4, all Ti elements are replaced by Ta elements, which will cause the generation of hard and brittle intermetallic compounds, resulting in the decrease of low-temperature toughness and elongation of the material, wherein the yield strength at 4.2 K decreases to 1.52 GPa, and the elongation at break at 77 K is only 23%. In Example 5, all Ta elements are replaced by Ti elements, which leads to the decrease of strengthening effect, and the tensile strength and yield strength at 77 K and 4.2 K are significantly decreased. Therefore, it is shown that the application preferably contains Ti and Ta as auxiliary elements, which can further improve the strength and plasticity of high-entropy alloy at low temperature.

[0102] (3) As can be seen from Examples 1 and 6, in Example 6, the addition of nitrogen element is too much, which will cause a large amount of nitride to precipitate, thereby reducing the low-temperature strength and toughness of the high-entropy alloy, and the elongation at break at 77 K is only 22%.

[0103] (4) As can be seen from Examples 1 and 7, in Example 7, the molar ratio of the sum of auxiliary elements to the elements in the base alloy is too high, which leads to the appearance of BCC phase and hard and brittle intermetallic compounds, thereby reducing the low-temperature strength and toughness of the high-entropy alloy, and the elongation at break at 77 K is only 15%, which is significantly decreased compared with 32% in Example 1.

[0104] (5) From the combination of Example 1 and Examples 8-9, it can be seen that the temperature of annealing treatment in Example 8 is 850℃, which causes the precipitated phase to be unable to be fully precipitated, and is easy to cause the precipitated phase to be coarsened and the grain size of the high-entropy alloy itself to be large, thereby reducing the low-temperature strength of the material, the temperature of annealing treatment in Example 9 is 500℃, which causes the segregation of elements and reduces the microstructure stability and low-temperature strength of the material; thus, it is shown that the present application preferably controls the temperature of annealing treatment in a reasonable range, which can significantly improve the low-temperature strength of the high-entropy alloy.

[0105] (6) From the combination of Example 1 and Example 10, it can be seen that the temperature of heat treatment in Example 10 is 800℃, which is too high, causing the grains to excessively grow, which is not conducive to the later cold rolling + annealing treatment, and it is difficult to obtain the desired fine-grained structure, causing the strength and toughness of the high-entropy alloy at low temperature to be reduced, and the elongation at break at 77K is only 24%; thus, it is shown that the present application preferably controls the temperature of heat treatment in a reasonable range, which can significantly improve the low-temperature strength and toughness of the high-entropy alloy.

[0106] (7) In Comparative Example 1, no N element is added, and in Example 1, the addition of the nitrogen element will increase the solid solution strengthening effect of the material, effectively hinder the dislocation movement, and realize the synergistic improvement of high strength and high toughness of the material; in Comparative Example 2, all the auxiliary elements are replaced by Al elements, which causes the low-temperature strength to be significantly reduced compared with Example 1, indicating that the present application selects Ti and Ta as auxiliary elements, which can better improve the low-temperature strength and toughness of the high-entropy alloy; in Comparative Example 3, no Ti and Ta elements are added, which causes the missing of the precipitated phase enhancement effect, and finally the low-temperature strength is significantly lower than that of Example 1; in Comparative Example 4, it does not have 5 elements, and is not a high-entropy alloy, and the low-temperature strength is significantly reduced.

[0107] The present application is described in detail by the above examples, but the present application is not limited to the above detailed features, i.e. it does not mean that the present application must rely on the above detailed features to be implemented. Those skilled in the art should understand that any improvement of the present application, equivalent replacement of the technical features selected by the present application, addition of auxiliary technical features, selection of specific modes, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. A high-entropy alloy for cryogenic use, characterized by, The high-entropy alloy comprises a base alloy, an N element, and an auxiliary element; The base alloy is Co a Cr b Fe c Ni d Mn e high-entropy alloy; The auxiliary element is Ti and Ta; The high-entropy alloy has a precipitated phase, the precipitated phase comprises any one of (Ni, Co, Fe)3Ti precipitated phase, (Ni, Co, Fe)3Ta precipitated phase, or (Ni, Co, Fe)3(Ti, Ta) precipitated phase, or a combination of at least two of them, the average grain size of the high-entropy alloy is 0.1-15 μm; the mass percentage of the N element in the high-entropy alloy is 0.02-0.07 wt%. The Co a Cr b Fe c Ni d Mn e The ratio of a, b, c, d, e in the high-entropy alloy is (0.001-1.5):(0.9-1.1):1:(0.9-1.1):(0.001-1), wherein a, b, c, d and e are the number of atoms; the molar ratio of the sum of the auxiliary elements and the elements in the base alloy in the high-entropy alloy is (0.001-0.2):1; the molar ratio of Ta and Ti in the high-entropy alloy is (0.05-0.15):

1. The preparation method of the high-entropy alloy comprises: (1) melting raw materials of the high-entropy alloy and suction casting into a water-cooled copper mold to obtain a cast high-entropy alloy material; (2) the high-entropy alloy material in step (1) is subjected to heat treatment and cold rolling to obtain a high-entropy alloy plate, wherein the cold rolling reduction is 75-90%; (3) the high-entropy alloy plate in step (2) is subjected to annealing treatment to obtain the low-temperature high-entropy alloy.

2. The high-entropy alloy of claim 1, wherein, The average grain size of the high-entropy alloy is 0.5-5 μm.

3. The high-entropy alloy of claim 1 or 2, wherein, The size of the precipitated phase ranges from 10 nm to 50 nm; And / or, the high-entropy alloy does not contain BCC phase and / or hard and brittle intermetallic compounds in the microstructure.

4. The high-entropy alloy of claim 1, wherein, The high-entropy alloy is CoCrFeNiMnTi 0.25 Ta 0.02 .

5. The high-entropy alloy of claim 1, wherein, The yield strength of the high-entropy alloy at 77 K is greater than 1.3 GPa, and the elongation is greater than 20%; And / or, the tensile strength of the high-entropy alloy at 77 K is greater than 1.6 GPa; And / or, the yield strength of the high-entropy alloy at 4.2 K is greater than 1.5 GPa; And / or, the tensile strength of the high-entropy alloy at 4.2 K is greater than 1.8 GPa.

6. A method for producing the high-entropy alloy for low temperature use according to any one of claims 1 to 5, characterized by, The preparation method comprises: (1) melting raw materials of the high-entropy alloy and suction casting into a water-cooled copper mold to obtain a cast high-entropy alloy material; (2) the high-entropy alloy material in step (1) is subjected to heat treatment and cold rolling to obtain a high-entropy alloy plate, wherein the cold rolling reduction is 75-90%; (3) the high-entropy alloy plate in step (2) is subjected to annealing treatment to obtain the low-temperature high-entropy alloy.

7. The preparation method according to claim 6, characterized in that, The melting in step (1) is vacuum arc melting; And / or, the number of times of melting is at least 5 times; And / or, the melting is carried out in an argon atmosphere.

8. The production method according to claim 6 or 7, characterized by, The heat treatment in step (2) is performed in a vacuum environment; wherein the vacuum degree of the heat treatment is ≤ 10 -5 Pa; And / or, the temperature of the heat treatment is 600-800 ℃; And / or, the time of the heat treatment is 6-10 h.

9. The production method according to claim 6 or 7, characterized by, The temperature of the annealing in step (3) is 650-750 ℃; And / or, the time of the annealing is 6-10 h.

10. Use of the low-temperature high-entropy alloy according to any one of claims 1-5 in aerospace, nuclear fusion, or accelerators.

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