A method for preparing high-strength and tough medium-entropy alloy

Abstract

The present invention relates to the field of metal material technology, and in particular to a method for preparing a high-strength and tough medium-entropy alloy. The composition of the medium-entropy alloy is (FeCoCrNi) 100‑x‑y Ti x Al y , 1≤x≤3, 4≤y≤9, Al and Ti elements are added to the FeCoCrNi medium entropy alloy, and the yield strength and hardness of the alloy are significantly improved by asynchronous cold rolling, deep cold asynchronous rolling and heat treatment. 100‑x‑y Ti x Al y Medium-entropy alloys are based on FCC solid solution and strengthened by L12 phase precipitation. Both the L12 ordered phase and the matrix phase have FCC structures and the interface between the two phases maintains a coherent relationship, ensuring the dispersed precipitation of the L12 phase. This not only improves the strength and toughness of the alloy, but also improves the creep resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal materials, and in particular relates to a method for preparing a high-strength and tough medium-entropy alloy. Background Art

[0002] High entropy alloys are single-phase solid solutions composed of five or more metal elements mixed in equiatomic or non-equiatomic ratios. However, high entropy alloys are brittle at room temperature and have low plasticity (often less than 2%), making them difficult to process. As the number of high entropy alloy components decreases, medium entropy alloys are formed, with structural entropy ranging from R to 1.5R (R is the gas constant 8.314 J·mol -1 ), has excellent properties such as high strength, high hardness, wear resistance, corrosion resistance and high temperature mechanical properties, and will have broad prospects and development potential in various fields in the future.

[0003] The FeCoCrNi medium-entropy alloy is a single-phase disordered solid solution alloy with an FCC crystal structure, exhibiting low yield strength. The excellent mechanical properties of medium-entropy alloys are primarily due to complex deformation mechanisms at the nanoscale. However, a major shortcoming of multi-principal element alloys is their moderate yield strength, which is primarily influenced by solid solution strengthening, making it difficult to produce finer microstructures through large deformations. In the compositional design of high-entropy alloys, the addition of Al and Ti elements easily precipitates a second phase, causing lattice distortion and a phase structure transformation in the alloy, which improves the tensile strength and hardness of the alloy and imparts good corrosion resistance. Summary of the Invention

[0004] The present invention aims to provide a method for preparing a high-strength and tough medium-entropy alloy, significantly improving the yield strength and hardness of the medium-entropy alloy, thereby obtaining an FeCoCrNi-based medium-entropy alloy with even superior performance. The present invention significantly enhances the mechanical properties of the alloy by adding Al and Ti elements to the alloy and combining arc melting, solution treatment and aging treatment, hot rolling, asynchronous cold rolling, deep-cold asynchronous rolling, and annealing.

[0005] In order to achieve the above object, the technical solution of the present invention is as follows:

[0006] A method for preparing a high-strength and tough medium-entropy alloy, wherein the composition of the medium-entropy alloy is (FeCoCrNi) 100-x- y Ti x Al y , 1≤x≤3, 4≤y≤9, the preparation method comprises the following steps:

[0007] Step 1: Using each element as raw material, weigh each metal element according to the molar ratio of Fe, Co, Cr, and Ni being 1:1:1:1;

[0008] Step 2: The alloy melting device is a non-consumable vacuum arc furnace. The raw materials are placed in a water-cooled copper crucible and the alloy melting device is vacuumed to 5.0×10 -3 Pa, and then filled with high-purity argon gas to 5.0×10 4 Pa, and then pumped to 5.0×10 -3 Pa, filled with high-purity argon gas to 2.0×10 4 Pa, and purge it twice with high-purity argon to expel the adsorbed active gases (O2, N2, CO2, etc.), and then evacuate to 5.0×10 -4 Pa, filled with 8.0×10 4 Pa argon was used as the protective gas, and the alloy ingot was melted 6 times. During the 6th melting, pure aluminum and pure titanium blocks were added according to the composition ratio. After the melting was completed, it was cooled in a water-cooled copper crucible for 30 minutes before being taken out to reduce the volatilization of low-melting-point elements.

[0009] Step 3, taking the ingot obtained in step 2 and forging it, heating it to a temperature of 1200-1250° C., keeping it warm for 60-80 minutes, and forging it at a temperature of 1100-1200° C. to obtain a forging blank;

[0010] Step 4: The forging blank obtained in step 3 is subjected to a two-stage heat treatment process of "solution + aging", wherein the solution heat treatment temperature is 950-1050°C, and the heat preservation is 1-2 hours; the aging heat treatment temperature is 600-800°C, and the heat preservation is 8-12 hours, followed by water quenching; the purpose of the solution heat treatment is to dissolve the FCC / L12 dual-phase structure and the L12 phase precipitated during the cooling process to ensure a single supersaturated FCC solid solution, and the heat preservation is carried out for a period of time to make the composition uniform; the purpose of the aging heat treatment is to allow the L12 phase to disperse and precipitate from the supersaturated FCC solid solution;

[0011] Step 5, the alloy obtained in step 4 is subjected to two-stage hot rolling, wherein the first stage starts at a rolling temperature of 1050-1100° C., is hot-rolled through 5 passes to a thickness of 12-14 mm, and then water-cooled, with a final rolling temperature of 850-900° C.; the second stage is kept at 1150-1200° C. for 40-60 minutes, starts at a rolling temperature of 1000-1050° C., is hot-rolled through 4 passes to a thickness of 2-4 mm, and then water-cooled to room temperature, with a final rolling temperature of 850-900° C.;

[0012] Step 6: annealing the hot-rolled plate obtained in step 5 by heating the plate to 1000-1100° C. at a heating rate of 10° C. / min, keeping the plate in vacuum for 10-15 hours, and then quenching the plate in water.

[0013] Step 7, pickling the hot-rolled plate obtained in step 6 and then performing three asynchronous cold rolling at room temperature, with the speed ratio of the rollers being 1.15 to 1.25;

[0014] Step 8: Place the cold-rolled sheet obtained in step 7 into a vacuum tube furnace for annealing, heating to 1000-1100° C. at a heating rate of 10° C. / min, keeping the temperature in vacuum for 10-15 hours, and then quenching with water;

[0015] Step 9, pickling the annealed plate obtained in step 8 and then performing cryogenic asynchronous rolling, using a four-roll cold rolling mill to perform single-pass cryogenic asynchronous rolling with a reduction rate of 40% to 50%, a roll speed ratio of 1.2 to 1.4, and a plate thickness of 0.4 to 1.6 mm;

[0016] Step 10: The rolled plate obtained in step 9 is subjected to a final annealing heat treatment in a vacuum tube furnace at a heating temperature of 600-700° C. for 60-80 minutes, with argon protection throughout the process, and water-cooled to room temperature to obtain the medium-entropy alloy.

[0017] Furthermore, in step 2, the raw materials are placed into a water-cooled copper crucible in order from low to high melting points to ensure that the high melting point materials are completely melted.

[0018] Furthermore, in step 3, the thickness of the forging blank is 30 to 40 mm.

[0019] Furthermore, in step 7, during the asynchronous cold rolling process, the lower roll is a slow roll, and the roll speed is always kept constant; the upper roll is a fast roll, and the upper roll speed is adjusted according to the speed ratio; the pass reduction rate of the first and last passes is 10% to 20%, the rolling force is 150 to 200 kN, and the lower roll speed is 0.5 to 0.7 m / s; the pass reduction rate of the middle pass is 20% to 30%, the rolling force is 200 to 300 kN, and the lower roll speed is 0.8 to 1.0 m / s.

[0020] Furthermore, in step 7, the hot-rolled plate is pickled with a hydrochloric acid solution having a mass concentration of 6% to 8%, the pickling temperature is 50 to 70° C., and the pickling time is 20 to 30 minutes to remove surface iron oxide scale.

[0021] Furthermore, in step 9, before deep cold asynchronous rolling, the rolling rollers are turned on and rotated at zero load, and the upper and lower working rollers of the rolling mill are cooled by using a nitrogen cooling spray gun of the rolling mill to achieve a surface temperature of the rolling rollers of -180 to -100°C, and then the rolled plate is quickly taken out for deep cold asynchronous rolling; during the deep cold asynchronous rolling process, the upper roller is a slow roller, and the roller speed is always kept constant, and the lower roller is a fast roller, and the roller speed of the lower roller is adjusted according to the speed ratio. The roller speed of the upper roller is 1.1 to 1.3 m / s, the roller speed of the lower roller is 1.32 to 1.82 m / s, and the rolling force is 400 to 500 kN.

[0022] Furthermore, in step 9, the annealed sheet is pickled with a hydrochloric acid solution having a mass concentration of 6% to 8% at a pickling temperature of 50 to 70° C. for 20 to 30 minutes to remove surface iron oxide scale.

[0023] The "asynchronous rolling" described in the present invention is carried out on a commercially available reversible asynchronous cold rolling mill. The asynchronous rolling is carried out on a reversible asynchronous cold rolling mill, where the two work rolls have the same diameter and the asynchronous rolling conditions are achieved by the difference in the rotational speed of the upper and lower work rolls.

[0024] The beneficial effects of the present invention are:

[0025] (FeCoNiCr) prepared by the present invention 100-x-y Ti x Al y Medium-entropy alloys are based on an FCC solid solution and are strengthened by L12 phase precipitation. Both the L12 ordered phase and the matrix phase have an FCC structure, and the interface between the two phases maintains a coherent relationship, ensuring the dispersed precipitation of the L12 phase. This not only enhances the alloy's strength and toughness, but also improves its creep resistance. L12-phase-strengthened medium-entropy alloys break the limitations of a single principal element based on nickel. The multi-principal element FCC / L12 dual-phase structure provided by the present invention exhibits excellent high-temperature comprehensive performance. Heat-resistant materials above 650°C are only nickel-based or nickel-cobalt-based high-temperature alloys. Medium-entropy heat-resistant alloys with operating temperatures above 650°C and high-melting-point heat-resistant alloys that break through the melting point limitations of nickel-based alloys have important practical research significance.

[0026] The present invention adopts an asynchronous cold rolling process, which changes the linear speed of the two sides of the plate during rolling, utilizes strong "rolling" deformation to increase the cumulative strain of the deformed austenite, and improves the yield strength and plasticity of the medium-entropy alloy by promoting recrystallization grain refinement. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The macroscopic morphology of the alloy plate after cryogenic asynchronous rolling in Example 3;

[0028] Figure 2 The metallographic structures of the surface layer and the center layer of the alloy plate after asynchronous cold rolling in Example 3 are shown in Figure 3. a is the metallographic structure of the upper surface layer, and b is the metallographic structure of the center layer.

[0029] Figure 3 FeCoCrNi and (FeCoCrNi) obtained in Example 3 92 Tensile engineering stress-strain curve of Ti3Al5 alloy. DETAILED DESCRIPTION

[0030] The following examples may enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0031] Example 1

[0032] The composition of medium entropy alloy is (FeCoCrNi) 92Ti3Al5, the preparation method comprises the following steps:

[0033] Step 1: Using each element as raw material, weigh each metal element according to the molar percentage of each element in the entropy alloy FeCoCrNi (Fe:Co:Cr:Ni=1:1:1:1), and then weigh and mix the ingredients according to the mass ratio converted by calculation;

[0034] Step 2: The alloy melting device is preferably a non-consumable vacuum arc furnace. To ensure that the high melting point material is completely melted, the materials are discharged in order from low to high melting points and placed in a water-cooled copper crucible. The material with the highest melting point is placed at the top. In order to discharge the adsorbed active gases (O2, N2, CO2, etc.), high-purity argon is used to purge it twice. The specific operation is: vacuum to 5.0×10 -3 Pa, and then filled with high-purity argon gas to 5.0×10 4 Pa, and then pumped to 5.0×10 -3 Pa, filled with high-purity argon gas to 2.0×10 4 Pa, and finally vacuumed to 5.0×10 -4 Pa, filled with 8.0×10 4 Pa argon was used as the protective gas; to ensure uniform alloy smelting, the alloy ingot was smelted 6 times, and pure aluminum and pure titanium blocks were added according to the composition ratio during the 6th smelting. After the smelting was completed, in order to reduce the volatilization of low-melting-point elements, it was cooled in a water-cooled copper crucible for 30 minutes before being taken out;

[0035] Step 3: Forging the ingot obtained in step 2 at a heating temperature of 1200° C. for 80 min, a forging temperature of 1100° C., and forging to a thickness of 40 mm;

[0036] Step 4: The forging blank obtained in step 3 is subjected to a two-stage heat treatment process of "solution + aging", that is, after solution heat treatment at 950°C for 2 hours, the sample is encapsulated in a vacuum quartz tube, subjected to aging heat treatment at 600°C for 12 hours, and then water quenched; the purpose of the solution heat treatment is to dissolve the FCC / L12 dual-phase structure and the L12 phase precipitated during the cooling process to ensure a single supersaturated FCC solid solution, and the heat is maintained for a period of time to make the composition uniform; the purpose of the aging heat treatment is to allow the L12 phase to disperse and precipitate from the supersaturated FCC solid solution;

[0037] Step 5, the alloy obtained in step 4 is subjected to two-stage hot rolling, wherein the first stage starts at a rolling temperature of 1050°C, is hot-rolled to 14 mm through 5 passes, and then water-cooled, and the final rolling temperature is 850°C. In the second stage, the alloy is kept at 1150°C for 60 minutes, starts at a rolling temperature of 1000°C, is hot-rolled to 4 mm through 4 passes, and then water-cooled to room temperature, and the final rolling temperature is 850°C.

[0038] Step 6: Take the hot-rolled plate obtained in step 5, place it in a vacuum tube furnace for annealing, heat it to 1000° C. at a heating rate of 10° C. / min, keep it in vacuum for 15 hours, and then quench it with water;

[0039] Step 7: After pickling, the hot-rolled plate obtained in step 6 is subjected to three asynchronous cold rolling passes at room temperature. The cold rolling process parameters are as follows: the speed ratio of the rollers is 1.15, the lower roller is a slow roller, and the roller speed is always kept constant; the upper roller is a fast roller, and the upper roller speed is adjusted according to the speed ratio; the pass reduction rate of the first and last passes is 10%, the rolling force is 150 kN, and the lower roller speed is 0.5 m / s; the pass reduction rate of the middle pass is 20%, the rolling force is 200 kN, and the lower roller speed is 0.8 m / s;

[0040] Step 8: The cold-rolled sheet obtained in step 7 is placed in a vacuum tube furnace for annealing, heated to 1000° C. at a heating rate of 10° C. / min, kept in vacuum for 15 h, and then water-quenched;

[0041] Step 9: Take the annealed plate obtained in step 8 and pickle it for cryogenic asynchronous rolling. Use a four-roll cold rolling mill to perform single-pass cryogenic asynchronous rolling with a reduction rate of 40%, and the final thickness is 1.6 mm. Before the cryogenic asynchronous rolling, turn on the rollers, rotate at zero load, and use the nitrogen cooling spray gun of the rolling mill to cool the upper and lower working rollers of the rolling mill. After the roller surface temperature reaches -100°C, quickly take out the rolled plate for cryogenic asynchronous rolling; change the roller speed. At this time, the upper roller is a slow roller, and the roller speed is always kept constant. The lower roller is a fast roller. The roller speed of the lower roller is adjusted according to the speed ratio. The speed ratio of the rollers is 1.2, the upper roller speed is 1.1 m / s, the lower roller speed is 1.32 m / s, and the rolling force is 400 kN.

[0042] Step 10: take the rolled plate obtained in step 9 and perform final annealing heat treatment in a vacuum tube furnace at a heating temperature of 600° C. for 80 minutes, with argon protection throughout the process, and water-cool to room temperature.

[0043] Example 2

[0044] The composition of medium entropy alloy is (FeCoCrNi) 92 Ti3Al5, the preparation method comprises the following steps:

[0045] Step 1 and step 2 are the same as in Example 1;

[0046] Step 3: Forging the ingot obtained in step 2 at a heating temperature of 1230° C. for 70 min and a forging temperature of 1150° C. until the ingot is forged to a thickness of 35 mm.

[0047] Step 4: The forging blank obtained in step 3 is subjected to a two-stage heat treatment process of "solution + aging", that is, after solution heat treatment at 1000°C for 1.5 hours, the sample is encapsulated in a vacuum quartz tube, subjected to aging heat treatment at 700°C for 10 hours, and then water quenched; the purpose of the solution heat treatment is to dissolve the FCC / L12 dual-phase structure and the L12 phase precipitated during the cooling process to ensure a single supersaturated FCC solid solution, and the heat is maintained for a period of time to make the composition uniform; the purpose of the aging heat treatment is to allow the L12 phase to disperse and precipitate from the supersaturated FCC solid solution;

[0048] Step 5, the alloy obtained in step 4 is subjected to two-stage hot rolling, wherein the first stage starts at a rolling temperature of 1070°C, is hot-rolled to 13 mm through 5 passes, and then water-cooled, and the final rolling temperature is 870°C. The second stage is kept at 1170°C for 50 minutes, starts at a rolling temperature of 1030°C, is hot-rolled to 3 mm through 4 passes, and then water-cooled to room temperature, and the final rolling temperature is 870°C.

[0049] Step 6: Take the hot-rolled plate obtained in step 5 and place it in a vacuum tube furnace for annealing treatment, heating it to 1050° C. at a heating rate of 10° C. / min, keeping it in vacuum for 12 hours, and then quenching it with water;

[0050] Step 7: After pickling, the hot-rolled plate obtained in step 6 is subjected to three asynchronous cold rolling passes at room temperature. The cold rolling process parameters are as follows: the speed ratio of the rollers is 1.2, the lower roller is a slow roller, the roller speed is always kept constant, the upper roller is a fast roller, and the upper roller speed is adjusted according to the speed ratio; the pass reduction rate of the first and last passes is 15%, the rolling force is 170 kN, and the lower roller speed is 0.6 m / s; the pass reduction rate of the middle pass is 25%, the rolling force is 250 kN, and the lower roller speed is 0.9 m / s;

[0051] Step 8: The cold-rolled sheet obtained in step 7 is placed in a vacuum tube furnace for annealing, heated to 1050° C. at a heating rate of 10° C. / min, kept in vacuum for 12 h, and then water quenched;

[0052] Step 9: Take the annealed plate obtained in step 8, pickle it, and then perform deep cold asynchronous rolling. Use a four-roll cold rolling mill to perform single-pass deep cold asynchronous rolling with a reduction rate of 45%, and the final thickness is 0.9 mm. Before the deep cold asynchronous rolling, turn on the rollers, rotate at zero load, and use the nitrogen cooling spray gun of the rolling mill to cool the upper and lower working rollers of the rolling mill. After the roller surface temperature reaches -140°C, quickly take out the rolled plate for deep cold asynchronous rolling; change the roller speed. At this time, the upper roller is a slow roller, and the roller speed is always kept constant. The lower roller is a fast roller. The roller speed of the lower roller is adjusted according to the speed ratio. The speed ratio of the rollers is 1.3, the upper roller speed is 1.2m / s, the lower roller speed is 1.56m / s, and the rolling force is 450kN.

[0053] Step 10: The rolled plate obtained in step 9 is subjected to final annealing heat treatment in a vacuum tube furnace at a heating temperature of 650° C. for 70 minutes, with argon protection throughout the process, and then cooled to room temperature with water.

[0054] Example 3

[0055] The composition of medium entropy alloy is (FeCoCrNi) 92 Ti3Al5, the preparation method comprises the following steps:

[0056] Step 1 and step 2 are the same as in Example 1;

[0057] Step 3: Forging the ingot obtained in step 2 at a heating temperature of 1250° C. for 60 min, a forging temperature of 1200° C., and forging to 30 mm;

[0058] Step 4: Take the forging blank obtained in step 3 and perform a two-stage heat treatment process of "solution + aging", that is, after solution heat treatment at 1050℃ for 1h, seal the sample in a vacuum quartz tube, perform aging heat treatment at 800℃ for 8h, and then water quench; the purpose of solution heat treatment is to dissolve the FCC / L12 dual-phase structure and the L12 phase precipitated during the cooling process, to ensure a single supersaturated FCC solid solution, and keep it warm for a period of time to make the composition uniform. The purpose of aging heat treatment is to allow the L12 phase to disperse and precipitate from the supersaturated FCC solid solution;

[0059] Step 5, the alloy obtained in step 4 is subjected to two-stage hot rolling, wherein the first stage starts at a rolling temperature of 1100°C, is hot-rolled to 12 mm through 5 passes, and then water-cooled, and the final rolling temperature is 900°C. The second stage is kept at 1200°C for 40 minutes, starts at a rolling temperature of 1050°C, is hot-rolled to 2 mm through 4 passes, and then water-cooled to room temperature, and the final rolling temperature is 900°C.

[0060] Step 6: Take the hot-rolled plate obtained in step 5, place it in a vacuum tube furnace for annealing, heat it to 1100° C. at a heating rate of 10° C. / min, keep it in vacuum for 10 hours, and then quench it in water;

[0061] Step 7: After pickling, the hot-rolled plate obtained in step 6 is subjected to three asynchronous cold rolling passes at room temperature. The cold rolling process parameters are as follows: the speed ratio of the rollers is 1.25, the lower roller is a slow roller, the roller speed is always kept constant, the upper roller is a fast roller, and the upper roller speed is adjusted according to the speed ratio; the pass reduction rate of the first and last passes is 20%, the rolling force is 200 kN, and the lower roller speed is 0.7 m / s; the pass reduction rate of the middle pass is 30%, the rolling force is 300 kN, and the lower roller speed is 1.0 m / s;

[0062] Step 8: The cold-rolled sheet obtained in step 7 is placed in a vacuum tube furnace for annealing, heated to 1100° C. at a heating rate of 10° C. / min, kept in vacuum for 10 h, and then water quenched;

[0063] Step 9, take the annealed plate obtained in step 8 and pickle it and then perform deep cold asynchronous rolling, use a four-roll cold rolling mill to perform single-pass deep cold asynchronous rolling with a reduction rate of 50%, and the final thickness is 0.4mm; before the deep cold asynchronous rolling, turn on the rollers, rotate at zero load, and use the nitrogen cooling spray gun of the rolling mill to cool the upper and lower working rollers of the rolling mill. After the roller surface temperature reaches -180°C, quickly take out the rolled plate for deep cold asynchronous rolling; change the roller speed, at this time the upper roller is a slow roller, the roller speed is always kept constant, the lower roller is a fast roller, and the roller speed of the lower roller is adjusted according to the speed ratio. The speed ratio of the rollers is 1.4, the upper roller speed is 1.3m / s, the lower roller speed is 1.82m / s, and the rolling force is 500kN;

[0064] Step 10: The rolled plate obtained in step 9 is subjected to final annealing heat treatment in a vacuum tube furnace at a heating temperature of 700° C. for 60 min under argon protection during the entire process and then cooled to room temperature with water.

[0065] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. The scope of protection of the present invention shall be determined by the scope defined in the claims. Other variations or modifications may be made based on the above description. Obvious variations or modifications derived therefrom shall remain within the scope of protection of the present invention.

Claims

1. A method for preparing a high-strength and tough medium-entropy alloy, characterized in that: The composition of the medium entropy alloy is (FeCoCrNi) 100-x-y Ti x Al y , 1≤x≤3, 4≤y≤9, the preparation method comprises the following steps: Step 1: Using each element as raw material, weigh each metal element according to the molar ratio of Fe, Co, Cr, and Ni being 1:1:1:1; Step 2: The alloy melting device is a non-consumable vacuum arc furnace. The raw materials are placed in a water-cooled copper crucible and the alloy melting device is vacuumed to 5.0×10 -3 Pa, and then filled with high-purity argon gas to 5.0×10 4 Pa, and then pumped to 5.0×10 -3 Pa, filled with high-purity argon gas to 2.0×10 4 Pa, and then evacuate to 5.0×10 -4 Pa, filled with 8.0×10 4 Pa argon was used as the protective gas, and the alloy ingot was melted 6 times. During the 6th melting, pure aluminum and pure titanium blocks were added according to the composition ratio. After the melting was completed, it was cooled in a water-cooled copper crucible for 30 minutes and then taken out; Step 3, taking the ingot obtained in step 2 and forging it, heating it to a temperature of 1200-1250° C., keeping it warm for 60-80 minutes, and forging it at a temperature of 1100-1200° C. to obtain a forging blank; Step 4: subjecting the forging blank obtained in step 3 to a two-stage heat treatment process of "solution + aging", wherein the solution heat treatment temperature is 950-1050°C, and the temperature is kept for 1-2 hours; the aging heat treatment temperature is 600-800°C, and the temperature is kept for 8-12 hours, followed by water quenching; Step 5, the alloy obtained in step 4 is subjected to two-stage hot rolling, wherein the first stage starts at a rolling temperature of 1050-1100° C., is hot-rolled through 5 passes to a thickness of 12-14 mm, and then water-cooled, with a final rolling temperature of 850-900° C.; the second stage is kept at 1150-1200° C. for 40-60 minutes, starts at a rolling temperature of 1000-1050° C., is hot-rolled through 4 passes to a thickness of 2-4 mm, and then water-cooled to room temperature, with a final rolling temperature of 850-900° C.; Step 6: annealing the hot-rolled plate obtained in step 5 by heating the plate to 1000-1100° C. at a heating rate of 10° C. / min, keeping the plate in vacuum for 10-15 hours, and then quenching the plate in water. Step 7, pickling the rolled plate obtained in step 6 and then performing three asynchronous cold rolling at room temperature, with the speed ratio of the rollers being 1.15 to 1.25; Step 8: Place the cold-rolled sheet obtained in step 7 into a vacuum tube furnace for annealing, heating to 1000-1100° C. at a heating rate of 10° C. / min, keeping the temperature in vacuum for 10-15 hours, and then quenching with water; Step 9, pickling the annealed plate obtained in step 8 and then performing cryogenic asynchronous rolling, using a four-roll cold rolling mill to perform single-pass cryogenic asynchronous rolling with a reduction rate of 40% to 50%, a roll speed ratio of 1.2 to 1.4, and a plate thickness of 0.4 to 1.6 mm; Step 10: The rolled plate obtained in step 9 is subjected to a final annealing heat treatment in a vacuum tube furnace at a heating temperature of 600-700° C. for 60-80 minutes, with argon protection throughout the process, and water-cooled to room temperature to obtain the medium-entropy alloy.

2. The preparation method according to claim 1, characterized in that In step 2, the raw materials are placed into a water-cooled copper crucible in order from low to high melting points to ensure that the high-melting-point materials are completely melted.

3. The preparation method according to claim 1, characterized in that In step 3, the thickness of the forging blank is 30 to 40 mm.

4. The preparation method according to claim 1, characterized in that In step 7, during the asynchronous cold rolling process, the lower roll speed is always kept constant, the pass reduction rate of the first and last passes is 10% to 20%, the rolling force is 150 to 200 kN, the lower roll speed is 0.5 to 0.7 m / s, the pass reduction rate of the middle pass is 20% to 30%, the rolling force is 200 to 300 kN, and the lower roll speed is 0.8 to 1.0 m / s.

5. The preparation method according to claim 1, characterized in that In step 7, the hot-rolled plate is pickled with a hydrochloric acid solution having a mass concentration of 6% to 8% at a pickling temperature of 50 to 70° C. for 20 to 30 minutes to remove surface iron oxide scale.

6. The preparation method according to claim 1, characterized in that In step 9, before deep cold asynchronous rolling, the rolling rollers are turned on and rotated at zero load, and the upper and lower working rollers of the rolling mill are cooled by the nitrogen cooling spray gun of the rolling mill to achieve a surface temperature of the rolling rollers of -180 to -100°C, and then the rolled plate is quickly taken out for deep cold asynchronous rolling; during the deep cold asynchronous rolling process, the upper roller speed is always kept constant, the upper roller speed is 1.1 to 1.3 m / s, the lower roller speed is 1.32 to 1.82 m / s, and the rolling force is 400 to 500 kN.

7. The preparation method according to claim 1, characterized in that In step 9, the annealed sheet is pickled with a hydrochloric acid solution having a mass concentration of 6% to 8% at a temperature of 50 to 70° C. for 20 to 30 minutes to remove surface iron oxide.

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