2500MPa-grade ultrahigh-strength high-entropy alloy and preparation method thereof

Abstract

The invention provides a 2500MPa-grade ultrahigh-strength high-entropy alloy and a preparation method thereof.The 2500MPa-grade ultrahigh-strength high-entropy alloy is prepared from, by mole, 39%-44% of Co, 27%-38% of Ni, 14%-22% of Cr, 2.5%-4.5% of Ti, 2.5%-4.5% of Al and 1%-3% of Mo, and Ti / Al is larger than or equal to 1 and smaller than or equal to 1.5; the preparation method comprises the steps that S1, all metal elements are taken for burdening, and an as-cast alloy ingot is obtained; s2, the alloy ingot is subjected to heat treatment and then quenched, and a solid solution state alloy ingot is obtained; s3, after deformation is applied to the solid solution state alloy ingot, heat treatment is conducted, and a first recrystallization alloy ingot is obtained; and S4, after deformation is applied to the first recrystallization alloy ingot, heat treatment is conducted, and the 2500MPa-grade ultrahigh-strength high-entropy alloy is obtained. The obtained high-entropy alloy has high strength and toughness, and the comprehensive mechanical property of the high-entropy alloy is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-entropy alloy preparation, and particularly relates to a 2500 MPa grade ultra-high strength high-entropy alloy and a preparation method thereof. Background Art

[0002] With the development of modern industrial technologies, people have increasingly higher requirements for the mechanical properties of structural materials. Among them, metal structural materials with ultra-high strength and high toughness at room temperature play an irreplaceable role. Traditional alloys are mainly composed of one alloying element, and alloying elements are added to regulate the alloy structure and properties. High-entropy alloys are solid-solution alloys formed by five or more near-equimolar alloying elements, which have characteristics such as high mixing entropy, slow atomic diffusion, and high lattice distortion. They can easily obtain solid solutions and nanostructures with high thermal stability, and exhibit excellent properties such as high hardness, high strength, high-temperature oxidation resistance, wear resistance, and corrosion resistance, showing great application potential. Therefore, high-entropy alloys have become high-performance metal materials with important application potential. In the existing high-entropy alloy systems, the yield strength of face-centered cubic structure high-entropy alloys is generally low. Although various strengthening and toughening mechanisms have been applied to this high-entropy alloy system in the latest research, it is very difficult for the mechanical properties of this high-entropy alloy to exceed 2 GPa. At the same time, the elongation of face-centered cubic structure high-entropy alloys with a strength exceeding 2.5 GPa is lower than 10%, which restricts the development and application of ultra-high strength high-entropy alloys.

[0003] Existing high-entropy alloy strengthening and toughening methods usually consider introducing high-density defects through large deformation, and then enhancing the alloy strength through defect strengthening. However, this method will seriously damage the toughness of the alloy. Therefore, heat treatment is needed to reduce the defect density and at the same time make the alloy undergo recrystallization behavior to restore the deformation ability. Therefore, after large deformation, how to effectively control the degree of recrystallization is the key to achieving strengthening and toughening. In addition, there are many methods for introducing large deformation, such as high-pressure torsion and equal-channel angular pressing, etc. However, these methods all have strict requirements and are not suitable for popularization. At the same time, after recrystallization, researchers also consider introducing precipitation phases to further improve the strength of high-entropy alloys. The key to precipitation strengthening is to effectively control the precipitation behavior so that the volume fraction of the precipitation phase is the largest while maintaining a small size. Since the precipitation behavior is also a thermally activated process and the volume fraction of the precipitation phase is different at different temperatures, the regulation is difficult. In terms of thermo-mechanical processes, the traditional process first introduces large deformation, then recrystallization heat treatment, and then precipitation heat treatment. The process is very complex. Therefore, how to effectively simplify the heat treatment process is also a current technical bottleneck.

[0004] Chinese invention patent CN 116162842 B discloses a high-strength high-entropy alloy and its preparation method. Using powders of Mn, Fe, Co, and Ni with equal atomic ratios as raw materials, sintering, cryogenic treatment, and annealing treatment are carried out to improve the mechanical properties of the single-phase alloy to 1525 MPa. However, there is a lack of further introduction of precipitation elements to achieve precipitation strengthening and an optimization idea of introducing deformation defect strengthening, resulting in a low strength of the obtained high-entropy alloy. Chinese invention patent CN116162875B discloses a heat treatment method for preparing a high-entropy alloy with compositional inhomogeneity and the prepared high-entropy alloy. The heat treatment process is first high-temperature solution heat treatment and rolling large deformation, then high-temperature crystallization heat treatment, and then low-temperature heat treatment to introduce precipitation phases. Before the low-temperature heat treatment, the second rolling large deformation is not carried out. Direct low-temperature treatment without large deformation will cause the alloy to lack high-density dislocation strengthening, and the strength value of the alloy is still low. In the above-mentioned prior art, in terms of improving the mechanical properties of high-entropy alloys, when introducing precipitation strengthening by heat treatment, less attention is paid to defect strengthening, resulting in limited strengthening effect of the alloy, and the tensile strength fails to exceed 2500 MPa. Summary of the Invention

[0005] Aiming at the deficiency that recrystallization and precipitation phases cannot be regulated simultaneously, the present invention provides a 2500 MPa grade ultra-high strength high-entropy alloy and its preparation method. The obtained high-entropy alloy has both high strength and toughness, improving the comprehensive mechanical properties of the high-entropy alloy.

[0006] The present invention is achieved through the following technical solutions: In the first aspect, the present invention provides a preparation method of a 2500 MPa grade ultra-high strength high-entropy alloy. The 2500 MPa grade ultra-high strength high-entropy alloy, in terms of mole percentage, includes the following metal components: Co 39% - 44%, Ni 27% - 38%, Cr 14% - 22%, Ti 2.5% - 4.5%, Al 2.5% - 4.5%, Mo 1% - 3%, 1 ≤ Ti / Al ≤ 1.5; where Ti / Al represents the molar ratio of Ti and Al; The preparation method includes the following steps: S1, according to the above mole percentage, take each metal element for batching to obtain an as-cast alloy ingot; S2, heat-treat the alloy ingot obtained in S1, and then perform quenching to obtain a solution-state alloy ingot; S3, apply a deformation amount of 60% - 70% to the solution-state alloy ingot obtained in S2 at room temperature, keep it at 1150 - 1200 °C for 5 - 20 min, and then perform quenching to obtain a first recrystallized alloy ingot; S4. After applying a deformation of 80% - 90% to the first recrystallized alloy ingot obtained in S3 at room temperature, hold it at 500 - 700 °C for 4 - 24 h, and then perform quenching to obtain a 2500 MPa grade ultra-high strength high-entropy alloy.

[0007] Preferably, in S1, a vacuum arc melting method is used to prepare a as-cast alloy ingot.

[0008] Preferably, in S2, the heat treatment temperature is 1150 - 1200 °C.

[0009] Preferably, in S2, the heat treatment time is 20 - 24 h.

[0010] Preferably, in S3, a room temperature rolling method is used to apply a deformation of 60% - 70%.

[0011] Preferably, in S4, a room temperature rolling method is used to apply a deformation of 80% - 90%.

[0012] In a second aspect, the present invention also provides a 2500 MPa grade ultra-high strength high-entropy alloy obtained by using the described preparation method.

[0013] Preferably, the room temperature tensile strength of the 2500 MPa grade ultra-high strength high-entropy alloy is 2510 - 2590 MPa.

[0014] Preferably, the room temperature elongation of the 2500 MPa grade ultra-high strength high-entropy alloy is 10.1% - 13.2%.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention conducts solution heat treatment on the as-cast high-entropy alloy sample obtained by melting to obtain a supersaturated solid solution alloy, providing a thermodynamic driving force for the precipitation behavior during the subsequent recrystallization-precipitation symbiotic heat treatment process; at the same time, large deformation in two passes is adopted to introduce distortion energy, and primary recrystallization is achieved by combining high-temperature short-time heat treatment. Low-temperature long-time heat treatment after deformation enables secondary recrystallization and precipitation behavior to occur simultaneously (recrystallization-precipitation symbiosis), realizing fine grain strengthening, introducing precipitation strengthening at the same time, and retaining a relatively high dislocation density. Mechanistically, choosing the low-temperature long-time heat treatment process after deformation can, on the one hand, enhance the deformation energy storage of the alloy through deformation to achieve dislocation strengthening, and on the other hand, the second recrystallization after deformation can restore a certain plasticity of the alloy, while the plasticity of the non-recrystallized alloy is poor. The low temperature is selected because the reduction rate of the dislocation density slows down at low temperatures, and at the same time, a relatively high volume fraction of precipitation phases can be ensured at this temperature, having great potential for precipitation strengthening; choosing a long time can activate the recrystallization behavior of the alloy to restore the plasticity of the alloy, because the recrystallization behavior requires a certain incubation period to proceed and a long time can enable the precipitation process to proceed fully, obtaining a better precipitation strengthening effect. If only recrystallization-precipitation symbiosis is carried out without the aforementioned primary recrystallization process, the fine grain strengthening effect of the alloy is poor, and the strength still cannot reach a relatively high level.

[0016] Due to the adoption of two-pass large-deformation room-temperature rolling and heat treatment processes at appropriate temperatures in the preparation method of the present invention, the alloy has a high density of dislocations, a high density of precipitation phases, and sub-micron recrystallized grains. The former two provide a high contribution of dislocation strengthening and precipitation strengthening, enabling the alloy to have a high yield strength. The latter can coordinate deformation to provide a high strain hardening ability, resulting in a high fracture strength (greater than 2500 MPa) and good toughness (greater than 10%). Moreover, the present invention uses Ti, Al, and Mo as the main alloying elements, where the contents of Ti and Al each reach 2.5 at% - 4.5 at%, and at the same time, the molar ratio of Ti and Al elements needs to satisfy the ratio 1 ≤ Ti / Al ≤ 1.5, enabling the alloy to have a good precipitation strengthening effect. At the same time, the content of precipitation phases enables the alloy to undergo large deformation to store high distortion energy and does not generate cracks. In addition, the content of Mo element reaches 1 at% - 3 at%. The grain boundary migration is affected by the solute drag effect, and the recrystallization behavior of the cold-deformed supersaturated solid solution alloy is inhibited, resulting in an obvious fine grain strengthening effect and retaining a high density of dislocations. At the same time, the Mo element itself has a certain solid solution strengthening effect. Therefore, the present invention solves the problem of low strength of face-centered cubic high-entropy alloys and manufactures a face-centered cubic high-entropy alloy with ultra-high strength and high toughness that takes into account strength and plasticity. Compared with the rolled alloy, it solves the problem that the strength and plasticity of high-entropy alloys cannot be improved simultaneously through simple heat treatment. The obtained ultra-high strength and high toughness high-entropy alloy has obvious advantages as a metal structural material (such as aircraft landing gears, vehicle bumpers, etc.) in extreme environments. In addition, the present invention realizes the comprehensive action of dislocation strengthening, precipitation strengthening, and fine grain strengthening in high-entropy alloys through simple room-temperature rolling deformation and heat treatment in an atmospheric environment. The process is simple, the cost is low, and the operability is strong, providing a simple, fast, and practical method for improving the mechanical properties of alloys. Description of the Drawings

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0018] Figure 1 Tensile property curves of the high-entropy alloys of Example 1, Comparative Example 1, and Comparative Example 2; Figure 2 Tensile property curves of the high-entropy alloys of Example 1, Comparative Example 3, and Comparative Example 4; Figure 3 Tensile property curves of the high-entropy alloys of Example 1, Comparative Example 5, and Comparative Example 6; Figure 4Tensile property curve of the high-entropy alloy of Example 2; Figure 5 Among them, (a) and (b) are microstructural pictures of the recrystallization-precipitation co-existing high-entropy alloy of Example 2. Specific implementation manners

[0019] The following uses specific specific examples to illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0020] It should be noted that the process equipment or devices not specifically specified in the following examples all adopt conventional equipment or devices in the art.

[0021] It should be noted that the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device including a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices. Moreover, unless otherwise specified, the numbers of each method step are only convenient tools for identifying each method step, rather than limiting the arrangement order of each method step or the scope in which the present invention can be implemented. The change or adjustment of their relative relationships, without substantially changing the technical content, should also be regarded as the scope in which the present invention can be implemented.

[0022] Considering that when the contents of Al and Ti are relatively low, the content of the L1 2 precipitation phase during the heat treatment process of the alloy is low, resulting in a reduced contribution of precipitation strengthening to the strength of the high-entropy alloy and a low tensile strength of the high-entropy alloy; while when the contents of Al and Ti are excessive, hard and brittle phases such as NiAl and η will be generated, making the workability of the high-entropy alloy poor, and the high-entropy alloy is prone to cracking and being scrapped during the thermomechanical treatment process, affecting the processing performance of the high-entropy alloy. In addition, under large deformation amounts, the recrystallization and grain growth behaviors of the high-entropy alloy during the heat treatment process are extremely likely to occur, weakening the grain refinement effect and making the contribution effect of fine grain strengthening to the alloy strength unstable; at the same time, grain boundary migration also causes obvious coarsening behavior of the precipitation phase, reducing the precipitation strengthening effect indirectly.

[0023] The present invention takes the simultaneous regulation of Ti, Al, and Mo elements as a breakthrough point, designs an ultra-high-strength high-entropy alloy based on Ni, Co, and Cr elements as the matrix, and through processes such as solution treatment, cold rolling, recrystallization treatment, secondary cold rolling, and recrystallization-precipitation co-existing heat treatment, obtains a high-entropy alloy with high-strength comprehensive mechanical properties.

[0024] Specifically, for the 2500 MPa grade ultra-high strength high-entropy alloy of the present invention, in terms of mole percentage, it includes the following metal components: Co 39% - 44%, Ni 27% - 38%, Cr 14% - 22%, Ti 2.5% - 4.5%, Al 2.5% - 4.5%, Mo 1% - 3%; 1 ≤ Ti / Al ≤ 1.5; where Ti / Al represents the molar ratio of Ti and Al.

[0025] The preparation method of the 2500 MPa grade ultra-high strength high-entropy alloy includes the following steps: S1, according to the above mole percentage, take each metal element for batching, and prepare to obtain an as-cast alloy ingot; S2, heat-treat the alloy ingot obtained in S1, and then perform quenching to obtain a solution-treated alloy ingot; S3, at room temperature, apply a deformation amount of 60% - 70% to the solution-treated alloy ingot obtained in S2, hold it at 1150 - 1200 °C for 5 - 20 min, and then perform quenching to obtain a first recrystallized alloy ingot; S4, at room temperature, apply a deformation amount of 80% - 90% to the first recrystallized alloy ingot obtained in S3, hold it at 500 - 700 °C for 4 - 24 h, and then perform quenching to obtain a 2500 MPa grade ultra-high strength high-entropy alloy.

[0026] In order to ensure that the high-entropy alloy has good strength and workability, the present invention first selects appropriate Al and Ti contents to make as much L1 2 precipitation phase generated in the high-entropy alloy, but the content is not too high to avoid the generation of harmful phases and maintain the good workability of the high-entropy alloy; then regulate the content of Mo element in the alloy. Through the solute drag migration interface effect, slow down the recrystallization behavior and grain growth behavior during the heat treatment process, maintain a good fine-grained strengthening effect, and at the same time can effectively control the reduction rate of the defect density, so that the dislocation strengthening effect can maintain a good effect during the heat treatment process. The addition of Mo element content is also beneficial to the improvement of the solution strengthening effect and the improvement of the comprehensive mechanical properties of the alloy.

[0027] In addition to the above main elements, the alloy proposed by the present invention also has other alloying elements, which play different roles. In terms of mole percentage, the ultra-high strength high-entropy alloy provided by the present invention includes Co 39 - 44%. In the present invention, the Co element can reduce the stacking fault energy of the system, increase the mixing entropy of the system at the same time, and improve the strain hardening ability to maintain phase stability. The ultra-high strength high-entropy alloy provided by the present invention includes Ni 27 - 38%. The Ni element has a face-centered cubic structure, can increase the mixing entropy of the system, and maintain the stability of the face-centered cubic phase of the alloy. The ultra-high strength high-entropy alloy provided by the present invention includes Cr 14 - 22%. The Cr element can increase the mixing entropy of the system and improve the heat resistance and corrosion resistance of the alloy.

[0028] More importantly, the preparation method of the present invention firstly performs solution heat treatment on the melted high entropy alloy cast sample to obtain a supersaturated solid solution alloy, which provides a thermodynamic driving force for the precipitation behavior in the subsequent recrystallization-precipitation symbiotic heat treatment process; then, two large deformations are used to introduce distortion energy, and high temperature and short time heat treatment are combined to realize the primary recrystallization, and low temperature and long time heat treatment are used to realize the secondary recrystallization and precipitation symbiotic behavior, thereby realizing fine grain strengthening, introducing precipitation strengthening, and retaining a relatively high dislocation density.

[0029] In a preferred embodiment of the present invention, the 2500MPa grade ultra-high strength high entropy alloy includes the following metal components in molar percentage: Co 39%~42%, Ni 29.5%~31%, Cr 17%~20%, Ti 2.5%~4.5%, Al 2.5%~4.5%, Mo 1%~3%; 1≤Ti / Al≤1.5. Within the preferred Ti / Al content ratio range of the present invention, a high entropy alloy with better mechanical properties can be obtained under the same process conditions.

[0030] In a specific embodiment of the present invention, in S1, a vacuum arc melting method is adopted to prepare a cast alloy ingot.

[0031] In a specific embodiment of the present invention, in S2, the heat treatment temperature is 1150-1200° C., and the heat treatment time is 20-24 hours.

[0032] In a specific embodiment of the present invention, in S3, a room temperature rolling method is used to apply a 60% to 70% deformation; in S4, a room temperature rolling method is used to apply a 80% to 90% deformation. The deformation process is simplified by the simple room temperature rolling deformation, which is easy to implement and suitable for promotion.

[0033] The present invention effectively designs the molar percentage content of each metal component, so that the ultra-high strength high entropy alloy composed of the raw materials with the above atomic percentage content has a face-centered cubic matrix structure at room temperature and also contains a large number of nano-scale precipitated phases; the average grain size of the high-strength high-entropy alloy prepared in a preferred embodiment of the present invention is 1 μm, and the average size of the precipitated phase is 15 nm (such as Figure 5 As shown); the obtained high entropy alloy increases the strength of the high entropy alloy synergistically through precipitation strengthening, dislocation strengthening, and heterogeneous deformation; when subjected to tensile stress load at room temperature, dislocation slip, heterogeneous deformation, grain rotation, etc. will occur, and the high entropy alloy maintains good toughness.

[0034] The experimental methods and detection methods described in the following embodiments are conventional methods unless otherwise specified; the reagents and materials are commercially available unless otherwise specified.

[0035] The following is a detailed description through the following examples and comparative examples.

[0036] Example 1 The high-entropy alloy in this example is composed of the following metal components in mole percentages: Co 41 at%, Ni 27 at%, Cr 22 at%, Ti 4.5 at%, Al 4.5 at%, Mo 1 at%; Ti / Al = 1.

[0037] The above high-entropy alloy is prepared according to the following steps: Step 1: According to the above mole percentages, the metal elements in the high-entropy alloy are proportioned to obtain 60 g of metal raw materials, which are placed in a crucible of a vacuum arc furnace. The vacuum is pumped to below 3×10 -3 Pa, and argon is filled to 0.05 MPa, and the gas washing is repeated once. The pre-melted titanium ingot is deoxidized for 3 minutes, and then other metal raw materials are melted. It is flipped and remelted 5 times to ensure uniform composition. The molten alloy is poured into a 12×10×8 mm mold, and the riser is cut off after cooling to obtain an as-cast alloy ingot; Step 2: The above alloy ingot is held at 1200 °C for 24 h, and then quenched to obtain a solution-treated alloy ingot; Step 3: After applying a 60% deformation amount to the solution-treated alloy ingot at room temperature, it is held at 1200 °C for 20 min, and then quenched to obtain a first recrystallized alloy ingot; Step 4: After applying an 80% deformation amount to the first recrystallized alloy ingot at room temperature, it is held at 500 °C for 4 h, and then quenched to obtain the final ultra-high strength, high toughness and high-entropy alloy.

[0038] Comparative Example 1 The high-entropy alloy in this comparative example is composed of the following metal components in mole percentages: Co 40 at%, Ni 30 at%, Cr 22 at%, Ti 3 at%, Al 4 at%, Mo 1 at%; Ti / Al = 0.75.

[0039] The preparation method of the high-entropy alloy in this comparative example is the same as that in Example 1.

[0040] Comparative Example 2 The high-entropy alloy in this comparative example is composed of the following metal components in mole percentages: Co 40 at%, Ni 30 at%, Cr 22 at%, Ti 4.5 at%, Al 2.5 at%, Mo 1 at%; Ti / Al = 1.8.

[0041] The preparation method of the high-entropy alloy in this comparative example is the same as that in Example 1.

[0042] Comparative Example 3 The composition of the high-entropy alloy in this comparative example is the same as that in Example 1. Steps 1 to 3 of the preparation method are the same as those in Example 1. The difference lies only in Step 4: The first recrystallized alloy ingot is held at 500 °C for 4 h, followed by quenching to obtain the final high-entropy alloy.

[0043] Comparative Example 4 The composition of the high-entropy alloy in this comparative example is the same as that in Example 1. Steps 1 to 2 of the preparation method are the same as those in Example 1. The difference lies only in that Step 3 is omitted, and Step 4 is: After applying a deformation amount of 80% to the solution-treated alloy ingot, it is held at 500 °C for 4 h, followed by quenching to obtain the final high-entropy alloy.

[0044] Comparative Example 5 The composition of the high-entropy alloy in this comparative example is the same as that in Example 1. Steps 1 to 3 of the preparation method are the same as those in Example 1. The difference lies only in that Step 4 is omitted, and the final high-entropy alloy is directly obtained through Steps 1 to 3.

[0045] Comparative Example 6 The composition of the high-entropy alloy in this comparative example is the same as that in Example 1. Steps 1 to 2 of the preparation method are the same as those in Example 1. The difference lies only in that the annealing temperature in Step 3 is reduced. After applying a deformation amount of 60% to the solution-treated alloy ingot at room temperature, it is held at 800 °C for 20 min, followed by quenching to obtain the first recrystallized alloy ingot; and Step 4 remains unchanged to obtain the final high-entropy alloy.

[0046] The room-temperature tensile mechanical properties of Example 1 are compared with those of Comparative Example 1 and Comparative Example 2 as Figure 1 shown. The high-entropy alloy of Example 1 was subjected to a tensile test at room temperature, and its yield strength and tensile strength (i.e., fracture strength) were 2260 MPa and 2530 MPa, respectively, and the elongation was 11.9%. The high-entropy alloy of Comparative Example 1 was subjected to a tensile test at room temperature, and its yield strength and tensile strength were 1800 MPa and 2030 MPa, respectively, which were significantly lower than those of the high-entropy alloy of Example 1. The high-entropy alloy of Comparative Example 2 was subjected to a tensile test at room temperature, and fracture occurred before the end of the elastic section, and there were no accurate yield strength and tensile strength measurement values.

[0047] The above comparative examples illustrate the importance of the molar ratio of Ti and Al. In the present invention, the molar ratio of Al and Ti needs to be controlled. In Example 1, the molar ratio of Ti and Al is 1, which is within the ideal precipitation element content range for improving the strength of the high-entropy alloy. In Comparative Example 1, the molar ratio of Ti and Al is 0.75, and the strength decreases; in Comparative Example 2, the molar ratio of Ti and Al is 1.8, which causes harmful phases to form in the high-entropy alloy, significantly increasing the brittleness, and the high-entropy alloy fails prematurely in the elastic section.

[0048] The room-temperature tensile mechanical properties of Example 1 are compared with those of Comparative Example 3 and Comparative Example 4 asFigure 2 As shown, the high-entropy alloy of Example 1 was subjected to a tensile test at room temperature, and its yield strength and tensile strength (i.e., fracture strength) were 2260 MPa and 2530 MPa, respectively. The high-entropy alloy of Comparative Example 3 was subjected to a tensile test at room temperature, and its yield strength and tensile strength were 1370 MPa and 1530 MPa, respectively, which were significantly lower than those of the high-entropy alloy of Example 1. The high-entropy alloy of Comparative Example 4 was subjected to a tensile test at room temperature, and its yield strength and tensile strength were 870 MPa and 1120 MPa, respectively, which were significantly lower than those of the high-entropy alloy of Example 1.

[0049] The above comparative examples respectively illustrate the importance of low-temperature heat treatment and primary recrystallization process after deformation. In Comparative Example 3, direct low-temperature heat treatment was carried out without the introduction of large deformation, lacking the contribution of high-density dislocation strengthening, resulting in lower yield and tensile strengths of the alloy. In Comparative Example 4, there was no primary recrystallization process, lacking the contribution of initial fine-grain strengthening, resulting in a lower defect density in the large-grain-size sample under the same deformation amount. Therefore, the contribution of dislocation strengthening was lower, and the yield and tensile strengths of the alloy were even lower.

[0050] The comparison of the room-temperature tensile mechanical properties between Example 1 and Comparative Examples 5 and 6 is as Figure 3 As shown, the high-entropy alloy of Example 1 was subjected to a tensile test at room temperature, and its yield strength and tensile strength (i.e., fracture strength) were 2260 MPa and 2530 MPa, respectively. The high-entropy alloy of Comparative Example 5 was subjected to a tensile test at room temperature, and its yield strength and tensile strength were 810 MPa and 1298 MPa, respectively, which were significantly lower than those of the high-entropy alloy of Example 1. The high-entropy alloy of Comparative Example 6 was subjected to a tensile test at room temperature, and its yield strength and tensile strength were 2005 MPa and 2135 MPa, respectively, which were significantly lower than those of the high-entropy alloy of Example 1.

[0051] The above comparative examples respectively illustrate the importance of the secondary recrystallization process and the importance of high-temperature annealing in the primary recrystallization process. In Comparative Example 5, the secondary recrystallization process was not carried out, and dislocation strengthening and precipitation strengthening were not introduced. Therefore, the yield and tensile strengths of the alloy were lower. In Comparative Example 6, the annealing temperature in the primary recrystallization process was reduced, and the primary recrystallization behavior of the alloy was not sufficient, reducing the workability of the alloy during secondary deformation. More cracks were introduced during rolling deformation, and finally the alloy failed prematurely due to more cracks during the tensile test.

[0052] Example 2 The high-entropy alloy of this example is composed of the following metal components in mole percentages: Co 39 at%, Ni 31 at%, Cr 20 at%, Ti 4.5 at%, Al 4.5 at%, Mo 1 at%; Ti / Al = 1.

[0053] The above high-entropy alloy is prepared according to the following steps: Step 1: According to the above molar percentages, each metal element in the high-entropy alloy is taken to obtain 60 g of metal raw materials, which are placed in a crucible of a vacuum arc furnace. The vacuum is pumped down to below 3×10 -3 Pa, and argon gas is filled to 0.05 MPa, and the gas washing is repeated once. The pre-melted titanium ingot is deoxidized for 3 minutes, and then the raw materials are melted. The melting is reversed and remelted 6 times to ensure uniform composition. The molten alloy is poured into a 12×10×8 mm mold, and the riser is cut off after cooling to prepare a as-cast alloy ingot; Step 2: The above alloy ingot is held at 1150 °C for 20 h, and then quenched to obtain a solution-treated alloy ingot; Step 3: After applying a 70% deformation amount to the solution-treated alloy ingot at room temperature, it is held at 1150 °C for 5 min, and then quenched to obtain a first recrystallized alloy ingot; Step 4: After applying a further 90% deformation amount to the first recrystallized alloy ingot at room temperature, it is held at 700 °C for 24 h, and then quenched to obtain the final ultra-high strength, high toughness and high-entropy alloy.

[0054] The room temperature tensile mechanical properties of the ultra-high strength, high toughness and high-entropy alloy obtained in Example 2 are as follows Figure 4 shown. The yield strength is 2310 MPa, the tensile strength is 2590 MPa, and the elongation rate remains at 13.2%. The electron micrograph of the ultra-high strength, high toughness and high-entropy alloy in Example 2 is as follows Figure 5 shown. From (a), high-density dislocations and high-density precipitates can be seen, where the size of the nano-precipitates is about 15 nm. From (b), the ultrafine grain structure (sub-micron grain structure) that plays a major role in ultra-high strength and high toughness can be seen, and the average grain size is 1 μm.

[0055] Examples 3-7 The ultra-high strength, high toughness and high-entropy alloys of Examples 3-7 are prepared according to the following steps: Step 1: According to the molar percentages in Table 1, each metal element in the alloy is proportioned to obtain 60 g of metal raw materials, which are placed in a crucible of a vacuum arc furnace. The vacuum is pumped down to below 3×10 -3 Pa, and argon gas is filled to 0.05 MPa, and the gas washing is repeated once. The pre-melted titanium ingot is deoxidized for 3 minutes, and then the raw materials are melted. The melting is reversed and remelted 6 times to ensure uniform composition. The molten alloy is poured into a 12×10×8 mm mold, and the riser is cut off after cooling to prepare a as-cast alloy ingot; Step 2: The above alloy ingot is held at 1200 °C for 24 h, and then quenched to obtain a solution-treated alloy ingot; Step 3: After applying a 70% deformation amount to the solution-treated alloy ingot at room temperature, it is held at 1200 °C for 10 min, and then quenched to obtain a first recrystallized alloy ingot; Step 4: After applying a 90% deformation to the first recrystallized alloy ingot at room temperature, keep it at 600 °C for 12 h, and then perform quenching to obtain the final ultra-high strength, high toughness and high entropy alloy.

[0056] Table 1 Composition and room temperature tensile mechanical property data of ultra-high strength, high toughness and high entropy alloys in Examples 3 - 6

[0057] As can be seen from the above examples, the Al and Ti contents provided by the present invention are respectively 2.5 - 4.5 atomic percentages, and the Ti / Al ratio is required to be between 1 and 1.5. The purpose is to keep the Ti / Al value between 1 and 1.5 to promote the generation of L1 2 coherent precipitation phases and improve the strength of the high entropy alloy. However, the ratio cannot be too high, otherwise the high entropy alloy is prone to embrittlement and its workability is greatly weakened; too low a ratio will cause a significant decrease in the alloy strength. At the same time, 1 - 3 atomic percentages of Mo element are added to the high entropy alloy. Through the solute hindrance effect of large atomic radius, the recrystallization behavior is slowed down, the coarsening of the precipitation phase during interface migration is avoided, and a good solid solution strengthening effect is also provided, thereby improving the comprehensive mechanical properties of the high entropy alloy.

[0058] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a 2500MPa ultra-high strength high entropy alloy, characterized in that: The 2500MPa ultra-high strength high entropy alloy comprises the following metal components in molar percentage: Co 39%-44%, Ni 27%-38%, Cr 14%-22%, Ti2.5%-4.5%, Al 2.5%-4.5%, Mo 1%-3%, 1.0≤Ti / Al≤1.5; wherein Ti / Al represents the molar ratio of Ti to Al; The preparation method comprises the following steps: S1, taking each metal element ingredient according to the above molar percentage to prepare a cast alloy ingot; S2, heat treating the alloy ingot obtained in S1, and then quenching it to obtain a solid solution alloy ingot; S3, after applying 60% to 70% deformation to the solid solution alloy ingot obtained in S2 at room temperature, keeping it at 1150 to 1200°C for 5 to 20 minutes, and then quenching it to obtain the first recrystallized alloy ingot; S4, after applying 80%~90% deformation to the first recrystallized alloy ingot obtained in S3 at room temperature, keeping it at 500~700℃ for 4~24h, and then quenching it to obtain 2500MPa grade ultra-high strength high entropy alloy.

2. The method for preparing a 2500MPa grade ultra-high strength high entropy alloy according to claim 1, characterized in that: In S1, a cast alloy ingot is prepared by a vacuum arc melting method.

3. The method for preparing a 2500MPa ultra-high strength high entropy alloy according to claim 1, characterized in that: In S2, the heat treatment temperature is 1150~1200℃.

4. The method for preparing a 2500MPa ultra-high strength high entropy alloy according to claim 1, characterized in that: In S2, the heat treatment time is 20~24h.

5. The method for preparing a 2500MPa ultra-high strength high entropy alloy according to claim 1, characterized in that: In S3, a room temperature rolling method is used to apply a deformation of 60% to 70%.

6. The method for preparing a 2500MPa ultra-high strength high entropy alloy according to claim 1, characterized in that: In S4, a room temperature rolling method is used to apply 80% to 90% deformation.

7. A 2500MPa grade ultra-high strength high entropy alloy obtained by the preparation method according to any one of claims 1 to 6.

8. The 2500MPa ultra-high strength high entropy alloy according to claim 7, characterized in that: The room temperature tensile strength of the 2500MPa grade ultra-high strength high entropy alloy is 2510~2590MPa.

9. The 2500MPa ultra-high strength high entropy alloy according to claim 7, characterized in that: The room temperature elongation of the 2500MPa grade ultra-high strength high entropy alloy is 10.1% to 13.2%.

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