A high-entropy alloy with a three-dimensional network-distributed gradient grain structure and its preparation method

Abstract

This invention discloses a high-entropy alloy with a three-dimensional network-distributed gradient grain structure. The high-entropy alloy is made from several high-entropy alloy powders with gradually increasing grain size from the surface to the interior as basic units, and adjacent high-entropy alloy powders are metallurgically bonded together. This invention also discloses a method for preparing the high-entropy alloy with a three-dimensional network-distributed gradient grain structure, which includes the following steps: 1. High-speed ball milling of the initial high-entropy alloy powder; 2. Vacuum drying; 3. High-pressure primary sintering; 4. Low-pressure, rapid secondary sintering. This invention obtains a high-entropy alloy with a three-dimensional network-distributed gradient grain structure by metallurgically bonding high-entropy alloy powders with gradually increasing grain size from the surface to the interior. This significantly improves the yield strength and uniform plasticity of the high-entropy alloy and exhibits isotropic mechanical properties, making it suitable for the field of high-entropy alloy preparation technology.

Description

Technical Field

[0001] This invention belongs to the field of high-entropy alloy preparation technology, and in particular relates to a high-entropy alloy with a three-dimensional network-distributed gradient grain structure and its preparation method. Background Technology

[0002] With the continuous innovation and application of high-end equipment and major national projects, the development of metallic materials with excellent comprehensive mechanical properties has become an urgent task. Traditional alloys, limited by a single main element, face bottlenecks in performance improvement. High-entropy alloys, composed of multiple main elements, can overcome compositional design limitations and utilize the synergistic effect of multiple elements, providing a new direction for the development of high-performance metallic materials. Compared to traditional alloys, high-entropy alloys generally exhibit higher strength and plasticity combinations, work hardening, and fracture toughness. However, the yield strength of these high-entropy alloys is generally below 200MPa~300MPa, greatly restricting their practical applications.

[0003] In the strategies for strengthening the composition optimization and structure control of high-entropy alloys, grain refinement has advantages such as low cost, broad applicability, and significant improvement effect. According to the classic Hall-Petch relationship, when the micron-sized grains are refined to ultrafine or nanocrystalline, the high-density grain boundaries can increase the yield strength of high-entropy alloys by 10 times or more. However, the reduced dislocation storage space and accelerated dislocation recovery rate lead to a severe decrease in uniform plasticity, less than 3%. How to overcome the strength-plasticity inversion dilemma faced by high-entropy alloys is currently a research hotspot.

[0004] Inspired by biomaterials in nature (such as bamboo and bone), gradient-structured metallic materials, fabricated by constructing micro-components in a multi-scale spatial gradient order, have attracted widespread attention in the academic community due to their ability to maintain excellent uniform plasticity while significantly improving yield strength. Gradient structure design can fully leverage the advantages of high strength in hard components, high plasticity in soft components, and the strain gradient synergy, coupling, and reinforcement mechanisms caused by asynchronous plastic deformation between components, thereby improving the overall mechanical properties of metallic materials.

[0005] Currently, various types of gradient nanocrystalline structures, gradient nanotwin structures, and gradient nanophase structures have been developed. For example, Hamed Shahmir et al. studied Co... 20 Cr 20 Fe 20 Mn 20 Ni 20 The alloy underwent equal-channel angular extrusion, introducing high-density dislocations and other lattice defects through severe plastic deformation, and refining the grain size to 130 nm. This effectively improved the yield strength and tensile strength of the nanocrystalline alloy, but the uniform elongation was only 2%. MN Hasan et al. from the University of Sydney, Australia, used rotational accelerated shot peening to treat Co... 20 Cr20 Fe 20 Mn 20 Ni 20 Gradient nanocrystals and deformed twin heterostructures distributed throughout the thickness direction were prepared in the alloy, with the outermost grain size being 110 nm and the core grain size being 8 μm. The yield strength and tensile strength of the sample were effectively improved, but the uniform elongation was 15%.

[0006] However, the mechanical properties of the gradient-structured high-entropy alloys prepared in the aforementioned studies exhibit significant anisotropy, with the gradient distribution characteristics limited to a single direction, lacking the ability to control the two-dimensional degrees of freedom across scales within a plane. Therefore, developing new preparation techniques to obtain cross-scale gradient structures and significantly improve the comprehensive mechanical properties of high-entropy alloys is a critical issue that urgently needs to be addressed. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a high-entropy alloy with a three-dimensional network-distributed gradient grain structure. This high-entropy alloy is made using high-entropy alloy powder with gradually increasing grain size from the surface inwards as the basic unit, achieving metallurgical bonding between adjacent high-entropy alloy powders to obtain a high-entropy alloy with a three-dimensional network-distributed gradient grain structure. This solves the problem that the gradient distribution characteristics of existing gradient-structured high-entropy alloys are limited to a single direction, resulting in a mismatch between strength and plasticity.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is: a high-entropy alloy with a three-dimensional network-distributed gradient grain structure, characterized in that the high-entropy alloy is made of several high-entropy alloy powders with grain sizes gradually increasing from the surface to the inside as basic units, and adjacent high-entropy alloy powders are metallurgically bonded; the grains on the surfaces of adjacent high-entropy alloy powders are interconnected to form a high-entropy alloy with a three-dimensional network-distributed gradient grain structure.

[0009] The above-mentioned high-entropy alloy with a three-dimensional network-distributed gradient grain structure is characterized in that the three-dimensional network-distributed gradient grain structure in the high-entropy alloy accounts for 50% to 100% of the total volume of the high-entropy alloy.

[0010] The above-mentioned high-entropy alloy with a three-dimensional network-distributed gradient grain structure is characterized in that the grain size on the surface of the basic unit is no greater than 500 nm.

[0011] This invention, by preferably using nanocrystals or ultrafine crystals with a grain size of no more than 500 nm on the surface of the basic unit, can significantly enhance the gradient effect of high-entropy alloy powder, thereby greatly improving the strength and plasticity of high-entropy alloy.

[0012] The above-mentioned high-entropy alloy with a three-dimensional network-distributed gradient grain structure is characterized in that the high-entropy alloy has a single-phase face-centered cubic crystal structure.

[0013] This invention selects a high-entropy alloy with a single-phase face-centered cubic crystal structure. The face-centered cubic structure is relatively stable, has low stacking fault energy, can suppress dislocation recovery, and has strong dislocation storage capacity. It can effectively refine the grain size to nanocrystals or ultrafine grains through deformation.

[0014] Meanwhile, this invention also discloses a method for preparing a high-entropy alloy with a three-dimensional network-distributed gradient grain structure, characterized in that the preparation method includes the following steps:

[0015] Step 1: Mix the initial high-entropy alloy powder with the liquid process control agent and ball mill it in an inert atmosphere. The ball milling speed is 400 rpm to 500 rpm and the ball milling time is 12 h to 24 h.

[0016] Step 2: Vacuum dry the high-entropy alloy powder after ball milling in Step 1 to obtain ball-milled alloy powder;

[0017] Step 3: Perform a first sintering on the ball milled alloy powder obtained in Step 2 to obtain a bulk high-entropy alloy material; the first sintering method is as follows: heat to 5℃~100℃ below the recrystallization temperature of the ball milled alloy powder, hold at the temperature, and then cool down; the pressure of the first sintering is 200MPa~400MPa.

[0018] Step 4: Perform secondary sintering on the bulk high-entropy alloy material obtained in Step 3 to obtain a high-entropy alloy with a three-dimensional network-distributed gradient grain structure; the secondary sintering method is as follows: heat to 5℃~100℃ above the recrystallization temperature of the ball-milled alloy powder and then directly cool down; the pressure of secondary sintering is 30MPa~50MPa.

[0019] This invention, by increasing the ball milling speed and shortening the ball milling time, can increase the strain rate and strain experienced by the initial high-entropy alloy powder, thereby increasing the defect accumulation rate and improving grain refinement efficiency. On the other hand, it can amplify the gradient distribution characteristics of the microstructure, avoiding structural homogenization and allowing the gradient grain structure to permeate the entire powder rather than being confined to a specific region. Furthermore, by increasing the ball milling speed within the range of 400 rpm to 500 rpm, the structural gradient in the gradient grain structure can be increased, enabling the preparation of nanocrystalline or ultrafine grain structures on the surface of the high-entropy alloy powder. Extending the ball milling time within the range of 12 h to 24 h can increase the volume fraction of the high-entropy alloy powder with the gradient grain structure.

[0020] This invention achieves minimal damage to the microstructure of ball-milled alloy powder by controlling the sintering methods of primary and secondary sintering, thereby significantly increasing the heterogeneity of the gradient structure of the ball-milled alloy powder.

[0021] The above-mentioned method for preparing a three-dimensional network-distributed gradient grain structure high-entropy alloy is characterized in that the initial high-entropy alloy powder in step one has a particle size of 100μm~150μm and the initial high-entropy alloy powder is spherical particles.

[0022] This invention, by selecting initial high-entropy alloy powder with a large particle size and spherical characteristics, can increase the collision frequency between the initial high-entropy alloy powder and stainless steel balls, which is beneficial to the uniform stress and plastic deformation of the initial high-entropy alloy powder.

[0023] The method for preparing a high-entropy alloy with a three-dimensional network-distributed gradient grain structure is characterized in that the ball milling process in step one is performed by milling for 30 minutes and then stopping for 10 minutes, and the liquid process control agent is ethanol or n-heptane.

[0024] The method for preparing a high-entropy alloy with a three-dimensional network-distributed gradient grain structure is characterized in that the vacuum drying temperature in step two is 20℃~30℃.

[0025] The above-mentioned method for preparing a high-entropy alloy with a three-dimensional network-distributed gradient grain structure is characterized in that the heating rate and cooling rate of the first sintering in step three are both 20℃ / min~30℃ / min, and the holding time is 5min~10min.

[0026] The above-mentioned method for preparing a high-entropy alloy with a three-dimensional network-distributed gradient grain structure is characterized in that the heating rate and cooling rate of the secondary sintering in step four are both 750℃ / min~950℃ / min.

[0027] This invention further shortens the secondary sintering time by controlling the heating and cooling rates of the secondary sintering, thereby suppressing excessive grain growth and achieving the goal of preserving the gradient deformation microstructure of the ball-milled alloy powder.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] 1. The high-entropy alloy of the present invention is made by using high-entropy alloy powder with gradually increasing grain size from the surface to the inside as the basic unit, so that adjacent high-entropy alloy powders are metallurgically bonded to obtain a high-entropy alloy with a three-dimensional network distribution of gradient grain structure. This greatly improves the yield strength and uniform plasticity of the high-entropy alloy, and exhibits isotropic mechanical properties. At the same time, the high-entropy alloy has a high proportion of gradient grain structure, which is distributed in all directions in three-dimensional space, and has two-dimensional distribution characteristics in any plane.

[0030] 2. The preparation method of this invention utilizes high-speed mechanical ball milling to induce severe plastic deformation of the initial high-entropy alloy powder under high strain rates and strains, forcing the grain size on the surface of the initial high-entropy alloy powder to refine. As the distance between the internal grains and the surface increases, the strain rate and strain gradually decrease, reaching their lowest values ​​at the core of the high-entropy alloy powder, where the degree of plastic deformation is weakest, essentially maintaining the original fine-grained structure. Ultimately, the ball-milled alloy powder forms a gradient microstructure with grain sizes gradually increasing from the surface to the interior. Then, a first sintering under high pressure and below the recrystallization temperature is performed on the ball-milled alloy powder to improve the density of the bulk high-entropy alloy material and promote defect recovery. A second sintering under low pressure, high speed, and above the recrystallization temperature is performed to improve the interfacial bonding between the powder particles within the high-entropy alloy, inhibit excessive grain growth, and retain the gradient deformation microstructure of the ball-milled alloy powder, thereby preparing a high-entropy alloy with a three-dimensional network-distributed gradient grain structure and good mechanical properties.

[0031] 3. By controlling the ball milling rate and time, this invention enables the ball-milled alloy powder to form a structure with nanocrystalline or ultrafine crystals on the surface and fine crystals in the core. Then, by controlling the temperature, pressure, heating and cooling rates during sintering, the sintering process minimizes the damage to the microstructure of the ball-milled alloy powder in the gradient deformation process. This results in a significantly increased heterogeneity in the prepared three-dimensional network gradient grain structure, further improving the yield strength and uniform plasticity of the high-entropy alloy.

[0032] 4. By adding a liquid process control agent during the ball milling process, this invention can prevent cold welding between the initial high-entropy alloy powders during the ball milling process; combined with the intermittent ball milling process, it avoids the ball milling jar from overheating due to continuous ball milling, which would cause the initial high-entropy alloy powder to cold weld on the ball milling jar or grinding balls.

[0033] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the internal structure of the high-entropy alloy powder of the present invention.

[0035] Figure 2 This is a schematic diagram of the internal structure of the high-entropy alloy of the present invention.

[0036] Figure 3 This is a metallographic image of the ball-milled alloy powder in Example 1 of the present invention.

[0037] Figure 4 This is a microstructure diagram of the high-entropy alloy prepared in Example 1 of the present invention.

[0038] Figure 5 This is a magnified microstructure of the high-entropy alloy prepared in Example 1 of the present invention.

[0039] Figure 6 The high-entropy alloys prepared in Examples 1 and 2 of this invention and Co 20 Cr 20 Fe 20 Mn 20 Ni 20 Stress-strain curve of the alloy. Detailed Implementation

[0040] Example 1

[0041] like Figure 1 and Figure 2 As shown, the high-entropy alloy in this embodiment is made of several high-entropy alloy powders with gradually increasing grain size from the surface to the core as basic units, and adjacent high-entropy alloy powders are metallurgically bonded; the grains on the surface of the adjacent high-entropy alloy powders are interconnected to form a high-entropy alloy with a three-dimensional network-distributed gradient grain structure; the gradient grain structure in the high-entropy alloy accounts for 100% of the total volume of the high-entropy alloy, and the grain size of the high-entropy alloy powder gradually increases from 400nm on the surface to 4μm in the core.

[0042] The preparation method of this embodiment includes the following steps:

[0043] Step 1: Prepare spherical Co particles with a diameter of 100μm~150μm. 20 Cr 20 Fe 20 Mn 20 Ni 20 Alloy powder and stainless steel balls were loaded into a vacuum ball milling jar at a mass ratio of 1:10, and ethanol was added. After the vacuum ball milling jar was evacuated, it was filled with argon gas and ball milled at 500 rpm for 12 hours in an argon atmosphere. The ball milling process consisted of grinding for 30 minutes and then stopping for 10 minutes.

[0044] Step 2: The high-entropy alloy powder after ball milling in Step 1 is vacuum dried at 20℃~30℃, and then argon gas is introduced to collect the powder, thus obtaining ball-milled alloy powder; the recrystallization temperature of the ball-milled alloy powder is 745℃.

[0045] Step 3: The ball-milled alloy powder obtained in Step 2 is sintered once using a spark plasma sintering device to obtain a bulk high-entropy alloy material. The method of the first sintering is as follows: the temperature is raised to 700°C at a rate of 28°C / min, held for 5 min, and then cooled at a rate of 28°C / min. The pressure of the first sintering is 200 MPa.

[0046] Step 4: Perform secondary sintering on the bulk high-entropy alloy material obtained in Step 3 to obtain a high-entropy alloy with a three-dimensional network-distributed gradient grain structure; the secondary sintering method is as follows: heat up to 750℃ at a rate of 750℃ / min and then cool down directly at a rate of 750℃ / min, and the pressure of the secondary sintering is 50MPa.

[0047] Metallographic analysis was performed on the ball-milled alloy powder obtained in step two of this embodiment, such as... Figure 3 As shown, most of the Co after ball milling 20 Cr 20 Fe 20 Mn 20 Ni 20 The alloy powder remained spherical and no cold welding occurred.

[0048] Microscopic analysis was performed on the high-entropy alloy prepared in this embodiment, such as... Figure 4 and Figure 5 As shown, the grain size of the high-entropy alloy powder in this high-entropy alloy gradually increases from 400 nm at the surface to 4 μm at the core, and the high-entropy alloy powder with a gradient grain structure accounts for 100% of the total volume of the high-entropy alloy. This high-entropy alloy prepared in this embodiment, and the spherical Co particles with a particle size of 100 μm to 150 μm... 20 Cr 20 Fe 20 Mn 20 Ni 20 Co obtained by alloy powder sintering 20 Cr 20 Fe 20 Mn 20 Ni 20 The alloy underwent uniaxial tensile testing, and the engineering stress-strain curve is shown below. Figure 6 As shown, the high-entropy alloy was measured to have a yield strength of 600 MPa, a tensile strength of 777 MPa, and a uniform elongation of 21%. The yield strength of this high-entropy alloy is approximately Co. 20 Cr 20 Fe 20 Mn 20 Ni 20 Twice the yield strength of the alloy, and its tensile strength is approximately that of Co. 20 Cr 20 Fe 20 Mn 20 Ni 20 The high entropy alloy has 1.3 times the tensile strength of the alloy, indicating that the yield strength and uniform plasticity of the high entropy alloy prepared in this embodiment are significantly improved.

[0049] Example 2

[0050] like Figure 1 and Figure 2As shown, the high-entropy alloy in this embodiment is made of several high-entropy alloy powders with gradually increasing grain size from the surface to the core as basic units, and adjacent high-entropy alloy powders are metallurgically bonded; the grains on the surface of the adjacent high-entropy alloy powders are interconnected to form a high-entropy alloy with a three-dimensional network-distributed gradient grain structure; the gradient grain structure in the high-entropy alloy accounts for 80% of the total volume of the high-entropy alloy, and the grain size of the high-entropy alloy powder gradually increases from 900nm on the surface to 10μm in the core.

[0051] The preparation method of this embodiment includes the following steps:

[0052] Step 1: Prepare spherical Co particles with a diameter of 100μm~150μm. 20 Cr 20 Fe 20 Mn 20 Ni 20 Alloy powder and stainless steel balls were loaded into a vacuum ball milling jar at a mass ratio of 1:10, and ethanol was added. After the vacuum ball milling jar was evacuated, it was filled with argon gas and ball milled at 400 rpm for 24 hours in an argon atmosphere. The ball milling process consisted of grinding for 30 minutes and then stopping for 10 minutes.

[0053] Step 2: The high-entropy alloy powder after ball milling in Step 1 is vacuum dried at 20℃~30℃, and then argon gas is introduced to collect the powder, thus obtaining ball-milled alloy powder; the recrystallization temperature of the ball-milled alloy powder is 600℃.

[0054] Step 3: The ball-milled alloy powder obtained in Step 2 is sintered once using a spark plasma sintering device to obtain a bulk high-entropy alloy material. The method of the first sintering is as follows: the temperature is raised to 500°C at a rate of 20°C / min, held for 5 min, and then cooled at a rate of 20°C / min. The pressure of the first sintering is 400 MPa.

[0055] Step 4: Perform secondary sintering on the bulk high-entropy alloy material obtained in Step 3 to obtain a high-entropy alloy with a three-dimensional network-distributed gradient grain structure; the secondary sintering method is as follows: heat to 700℃ at a rate of 700℃ / min and then cool down directly at a rate of 700℃ / min, the pressure of the secondary sintering is 40MPa.

[0056] Upon inspection, the grain size of the high-entropy alloy powder prepared in this embodiment gradually increases from 900 nm at the surface to 10 μm at the core, with the high-entropy alloy powder exhibiting a gradient grain structure accounting for 80% of the total volume of the high-entropy alloy. Uniaxial tensile testing was performed on this high-entropy alloy, and the engineering stress-strain curve is shown below. Figure 6As shown, the yield strength of the high-entropy alloy was measured to be 430 MPa, the tensile strength to be 700 MPa, and the uniform elongation to be 28%; indicating that the yield strength and uniform plasticity of the high-entropy alloy prepared in this embodiment were significantly improved.

[0057] Example 3

[0058] like Figure 1 and Figure 2 As shown, the high-entropy alloy in this embodiment is made of several high-entropy alloy powders with gradually increasing grain size from the surface to the core as basic units, and adjacent high-entropy alloy powders are metallurgically bonded; the grains on the surface of the adjacent high-entropy alloy powders are interconnected to form a high-entropy alloy with a three-dimensional network-distributed gradient grain structure; the gradient grain structure in the high-entropy alloy accounts for 70% of the total volume of the high-entropy alloy, and the grain size of the high-entropy alloy powder gradually increases from 1 μm on the surface to 8 μm in the core.

[0059] The preparation method of this embodiment includes the following steps:

[0060] Step 1: Prepare spherical Co particles with a diameter of 100μm~150μm. 20 Cr 20 Fe 20 Mn 20 Ni 20 Alloy powder and stainless steel balls were loaded into a vacuum ball milling jar at a mass ratio of 1:10, and ethanol was added. After the vacuum ball milling jar was evacuated, it was filled with argon gas and ball milled at 400 rpm for 18 hours in an argon atmosphere. The ball milling process consisted of grinding for 30 minutes and then stopping for 10 minutes.

[0061] Step 2: The high-entropy alloy powder after ball milling in Step 1 is vacuum dried at 20℃~30℃, and then argon gas is introduced to collect the powder, thus obtaining ball-milled alloy powder; the recrystallization temperature of the ball-milled alloy powder is 850℃.

[0062] Step 3: The ball-milled alloy powder obtained in Step 2 is sintered once using a spark plasma sintering device to obtain a bulk high-entropy alloy material. The method of the first sintering is as follows: the temperature is raised to 750°C at a rate of 30°C / min, held for 5 min, and then cooled at a rate of 30°C / min. The pressure of the first sintering is 300 MPa.

[0063] Step 4: Perform secondary sintering on the bulk high-entropy alloy material obtained in Step 3 to obtain a high-entropy alloy with a three-dimensional network-distributed gradient grain structure; the secondary sintering method is as follows: heat to 950℃ at a rate of 950℃ / min and then cool down directly at a rate of 950℃ / min, the pressure of the secondary sintering is 30MPa.

[0064] Upon inspection, the grain size of the high-entropy alloy powder prepared in this embodiment gradually increases from 1 μm on the surface to 8 μm in the core, and the high-entropy alloy powder with a gradient grain structure accounts for 70% of the total volume of the high-entropy alloy. Uniaxial tensile testing was performed on the high-entropy alloy, and the yield strength was measured to be 322 MPa, the tensile strength to be 609 MPa, and the uniform elongation to be 32%; indicating that the yield strength and uniform plasticity of the high-entropy alloy prepared in this embodiment are significantly improved.

[0065] Example 4

[0066] like Figure 1 and Figure 2 As shown, the high-entropy alloy in this embodiment is made of several high-entropy alloy powders with gradually increasing grain size from the surface to the core as basic units, and adjacent high-entropy alloy powders are metallurgically bonded; the grains on the surface of the adjacent high-entropy alloy powders are interconnected to form a high-entropy alloy with a three-dimensional network-distributed gradient grain structure; the gradient grain structure in the high-entropy alloy accounts for 100% of the total volume of the high-entropy alloy, and the grain size of the high-entropy alloy powder gradually increases from 180nm on the surface to 5μm in the core.

[0067] The preparation method of this embodiment includes the following steps:

[0068] Step 1: Spherical CoCrNi alloy powder with a particle size of 100μm~150μm and stainless steel balls are loaded into a vacuum ball milling jar at a mass ratio of 1:10, and ethanol is added. After evacuating the vacuum ball milling jar, argon gas is introduced, and ball milling is carried out at a speed of 480 rpm for 20 hours in an argon atmosphere. The ball milling process is to stop for 10 minutes after every 30 minutes of ball milling.

[0069] Step 2: The high-entropy alloy powder after ball milling in Step 1 is vacuum dried at 20℃~30℃, and then argon gas is introduced to collect the powder, thus obtaining ball-milled alloy powder; the recrystallization temperature of the ball-milled alloy powder is 685℃.

[0070] Step 3: The ball-milled alloy powder obtained in Step 2 is sintered once using a spark plasma sintering device to obtain a bulk high-entropy alloy material. The method of the first sintering is as follows: the temperature is raised to 680°C at a rate of 24°C / min, held for 5 min, and then cooled at a rate of 24°C / min. The pressure of the first sintering is 400 MPa.

[0071] Step 4: Perform secondary sintering on the bulk high-entropy alloy material obtained in Step 3 to obtain a high-entropy alloy with a three-dimensional network-distributed gradient grain structure; the secondary sintering method is as follows: heat up to 750℃ at a rate of 750℃ / min and then cool down directly at a rate of 750℃ / min, and the pressure of the secondary sintering is 50MPa.

[0072] Upon inspection, the grain size of the high-entropy alloy powder prepared in this embodiment gradually increases from 180 nm on the surface to 5 μm in the core, with the high-entropy alloy powder exhibiting a gradient grain structure accounting for 100% of the total volume of the high-entropy alloy. Uniaxial tensile testing of the high-entropy alloy yielded a yield strength of 780 MPa, a tensile strength of 900 MPa, and a uniform elongation of 21%, indicating a significant improvement in the yield strength and uniform plasticity of the high-entropy alloy prepared in this embodiment.

[0073] Example 5

[0074] like Figure 1 and Figure 2 As shown, the high-entropy alloy in this embodiment is made of several high-entropy alloy powders with gradually increasing grain size from the surface to the core as basic units, and adjacent high-entropy alloy powders are metallurgically bonded; the grains on the surface of the adjacent high-entropy alloy powders are interconnected to form a high-entropy alloy with a three-dimensional network-distributed gradient grain structure; the gradient grain structure in the high-entropy alloy accounts for 90% of the total volume of the high-entropy alloy, and the grain size of the high-entropy alloy powder gradually increases from 240nm on the surface to 8μm in the core.

[0075] The preparation method of this embodiment includes the following steps:

[0076] Step 1: Prepare spherical Al particles with a diameter of 100μm~150μm. 0.1 CoCrFeNi alloy powder and stainless steel balls were loaded into a vacuum ball milling jar at a mass ratio of 1:10, and n-heptane was added. After evacuating the vacuum ball milling jar, argon gas was introduced, and ball milling was carried out at a speed of 430 rpm for 22 hours in an argon atmosphere. The ball milling process consisted of grinding for 30 minutes and then stopping for 10 minutes.

[0077] Step 2: The high-entropy alloy powder after ball milling in Step 1 is vacuum dried at 20℃~30℃, and then argon gas is introduced to collect the powder, thus obtaining ball-milled alloy powder; the recrystallization temperature of the ball-milled alloy powder is 700℃.

[0078] Step 3: The ball-milled alloy powder obtained in Step 2 is sintered once using a spark plasma sintering device to obtain a bulk high-entropy alloy material. The method of the first sintering is as follows: the temperature is raised to 650°C at a rate of 26°C / min, held for 10 min, and then cooled at a rate of 26°C / min. The pressure of the first sintering is 250 MPa.

[0079] Step 4: Perform secondary sintering on the bulk high-entropy alloy material obtained in Step 3 to obtain a high-entropy alloy with a three-dimensional network-distributed gradient grain structure; the secondary sintering method is as follows: heat to 800℃ at a rate of 800℃ / min and then cool down directly at a rate of 800℃ / min; the pressure of the secondary sintering is 45MPa.

[0080] Upon inspection, the grain size of the high-entropy alloy powder prepared in this embodiment gradually increases from 240 nm on the surface to 8 μm in the core, with the high-entropy alloy powder exhibiting a gradient grain structure accounting for 90% of the total volume of the high-entropy alloy. Uniaxial tensile testing of the high-entropy alloy yielded a yield strength of 705 MPa, a tensile strength of 846 MPa, and a uniform elongation of 20%, indicating a significant improvement in the yield strength and uniform plasticity of the high-entropy alloy prepared in this embodiment.

[0081] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modifications, alterations, or equivalent structural transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a three-dimensional network distributed gradient grain structure high-entropy alloy, characterized in that, The high-entropy alloy is made of several high-entropy alloy powders with gradually increasing grain size from the surface to the inside as basic units, and adjacent high-entropy alloy powders are metallurgically bonded; the grains on the surface of the adjacent high-entropy alloy powders are interconnected to form a high-entropy alloy with a three-dimensional network-distributed gradient grain structure. The preparation method includes the following steps: Step 1: Mix the initial high-entropy alloy powder with the liquid process control agent and ball mill it in an inert atmosphere. The ball milling speed is 400 rpm to 500 rpm and the ball milling time is 12 h to 24 h. Step 2: Vacuum dry the high-entropy alloy powder after ball milling in Step 1 to obtain ball-milled alloy powder; Step 3: Perform a first sintering on the ball milled alloy powder obtained in Step 2 to obtain a bulk high-entropy alloy material; the first sintering method is as follows: heat to 5℃~100℃ below the recrystallization temperature of the ball milled alloy powder, hold at the temperature, and then cool down; the pressure of the first sintering is 200MPa~400MPa. Step 4: Perform secondary sintering on the bulk high-entropy alloy material obtained in Step 3 to obtain a high-entropy alloy with a three-dimensional network-distributed gradient grain structure. The secondary sintering method is as follows: heat the material to 5℃~100℃ above the recrystallization temperature of the ball-milled alloy powder and then cool it down directly. The pressure of the secondary sintering is 30MPa~50MPa. The heating rate and cooling rate of the secondary sintering are both 750℃ / min~950℃ / min.

2. The method of claim 1, wherein the three-dimensional net-like distributed gradient grain structure high-entropy alloy is prepared by the following steps of: The three-dimensional network-distributed gradient grain structure within the high-entropy alloy accounts for 50% to 100% of the total volume of the high-entropy alloy. ​ 3. The method of claim 1, wherein the three-dimensional net-like distributed gradient grain structure high-entropy alloy is prepared by the following steps of: The grain size on the surface of the basic unit is no greater than 500 nm. ​ 4. The method of claim 1, wherein the three-dimensional net-like distributed gradient grain structure high-entropy alloy is prepared by the following steps of: The high-entropy alloy has a single-phase face-centered cubic crystal structure. ​ 5. The method for preparing a high-entropy alloy with a three-dimensional network-distributed gradient grain structure according to claim 1, characterized in that, The initial high-entropy alloy powder mentioned in step one has a particle size of 100μm~150μm and is spherical.

6. The method for preparing a high-entropy alloy with a three-dimensional network-distributed gradient grain structure according to claim 1, characterized in that, The ball milling process in step one involves milling for 30 minutes and then stopping for 10 minutes. The liquid process control agent is ethanol or n-heptane.

7. The method for preparing a high-entropy alloy with a three-dimensional network-distributed gradient grain structure according to claim 1, characterized in that, The vacuum drying temperature in step two is 20℃~30℃.

8. The method for preparing a high-entropy alloy with a three-dimensional network-distributed gradient grain structure according to claim 1, characterized in that, In step three, the heating and cooling rates for the first sintering are both 20℃ / min to 30℃ / min, and the holding time is 5min to 10min.

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