Preparation method of biomimetic brick clay structure high strain energy density CoCrNi medium entropy alloy

Abstract

The application discloses a preparation method of a high-strain-energy-density CoCrNi medium-entropy alloy with a biomimetic brick clay structure, mainly comprising the following steps: firstly, cold-rolling a bulk CoCrNi alloy raw material, then annealing and water quenching to room temperature; and then, adopting high-speed rolling to perform multi-pass surface nanocrystallization treatment on the front and back surfaces of the annealed bulk CoCrNi alloy, so that the grain size has gradient structure and layered structure in two-dimensional space, respectively, and the prepared CoCrNi medium-entropy alloy comprises two layers of unevenly distributed gradient nanocrystalline layers and a uniformly distributed coarse-grained layer between the two layers, and has a very high strain energy density (strong plastic product). The application can prepare alloy plates with different sizes of transverse and longitudinal alternating brick clay structures to realize different heterogeneous strengthening effects. The application has simple process and strong universality, and can be popularized to other metal material processing fields.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials, specifically relating to a method for preparing a biomimetic brick-and-mortar structure high strain energy density CoCrNi medium entropy alloy. Background Technology

[0002] Metallic materials are key materials for high-end equipment and major engineering projects. With the development of industries such as aerospace, defense, and shipbuilding, higher demands are being placed on the performance of metallic materials. Therefore, traditional alloying methods based on a single element are no longer sufficient to meet the requirements of high strength and high plasticity. (Ye Junwei, 2004) [1] A multi-principal alloy design concept is proposed, which uses a mixture of multiple elements in equal or near-equal atomic ratios. By increasing the mixing entropy of the alloy system, the Gibbs free energy is reduced, forming a simple solid solution phase with short-range order and exhibiting excellent performance. Therefore, it has a wider application potential compared to traditional metallic materials.

[0003] As a novel multi-principal alloy system, the ternary medium-entropy alloy CoCrNi has attracted widespread attention from researchers since its first report in 2016. Reference [2] points out that CoCrNi has a tensile strength and fracture strain of 1 GPa and 70% at room temperature, and a fracture toughness higher than 200 MPa·m. 1 / 2 At -196℃, the tensile strength and fracture strain of the CoCrNi medium-entropy alloy can increase to 1.3 GPa and 90%, respectively, and the fracture toughness can reach 275 MPa·m. 1 / 2 Although CoCrNi medium-entropy alloys exhibit high tensile strength and excellent ductility at room temperature and low temperatures, their yield strength is low. Tensile tests on CoCrNi medium-entropy alloys at room temperature revealed a yield strength of only 360 MPa. [3] It cannot meet the requirements of engineering applications.

[0004] Some scholars have proposed that the product of yield strength and plasticity is essentially an approximation of strain energy density or tensile toughness, and can be used as an indicator for evaluating the strength-plasticity combination. [4] In other words, the higher the strain energy density, the better the strength-plasticity match. To improve the yield strength of CoCrNi medium-entropy alloys, researchers have adopted various strengthening methods, such as adding other elements to form a second phase, precipitation strengthening, and grain refinement strengthening. However, while these methods improve strength, they inevitably reduce plasticity, resulting in a contradictory strength-plasticity inversion relationship in the alloy.

[0005] In recent years, researchers have proposed constructing heterogeneous structures (such as gradient structures) to address this issue. [5] Layered structure [6]Strategies to improve the strength-plasticity balance in metallic materials. Geometrically necessary dislocation accumulation at heterogeneous interfaces induces long-range back stress in the soft region (mud region) and forward stress in the hard region (brick region). The coupling effect of these two factors manifests as macroscopic back stress strengthening. Furthermore, the mutual constraint between soft and hard components helps alleviate strain localization and maintain high plastic deformation stability.

[0006] [References]

[0007] [1] Yeh JW et al. published “Nanostructured High-Entropy Alloys with Multiple Principal Elements: Novel Alloy Design Concepts and Outcomes” in Advanced Engineering Materials, 2004, 6(5), 299-303.

[0008] [2] Bernd Gludovatz et al. published “Exceptional damage-tolerance of a medium-entropy alloy CrCoNi at cryogenic temperatures” in Nature Communications, 2016, 7(1): 10602.

[0009] [3] G. Laplanche et al. published “Reasons for the superior mechanical properties of medium-entropy CrCoNi compared to high-entropy CrMnFeCoNi” in Acta Materialia, 2017, 128:292-303.

[0010] [4] Wang YF et al. published “The optimum grain size for strength-ductility combination in metals” in the International Journal of Plasticity, 2023, 164:103574.

[0011] [5] Lu K. “Making strong nanomaterials ductile with gradients” published in Science, 2014, 345(6203):1455-1456.

[0012] [6] Wu XL et al. published “Heterogeneous lamellastructure unites ultrafine-grain strength with coarse-grain ductility” in Proceedings of the National Academy of Sciences, 2015, 112(47):14501-14505.

[0013] [7] Deng HW et al. published “Tailoring mechanical properties of a CoCrNi medium-entropy alloy by controlling nanotwin-HCP lamellae and annealing twins” in Materials Science and Engineering:A, 2019, 744:241-246.

[0014] [8] Wang JY et al. published “Ultrastrong and ductile (CoCrNi)” in the Journal of Materials Science & Technology, 2023, 135:241-249. 94Ti3Al3 medium-entropy alloys via introducing multi-scale heterogeneous structures (CoCrNi) 94 Ti3Al3 medium entropy alloy).

[0015] [9] Gu GH et al. published “Fabrication of structural and compositional heterostructured CoCrNi-CoCrFeMnNi multi-material using direct energy deposition additive manufacturing” in Intermetallics, 2022, 151:107726.

[0016]

[10] Guo FJ et al. published “Enhancing cryogenic tensile properties of CrCoNi mediumentropy alloy via heterogeneous microstructure design” in Materials Characterization, 2023, 201: 112951. Summary of the Invention

[0017] In view of the above-mentioned prior art, the present invention provides a method for preparing a biomimetic brick-and-mortar structure with high strain energy density CoCrNi. The method adopts the concept of heterogeneous toughening, so that the grain size of the CoCrNi medium-entropy alloy has a gradient structure and a layered structure in two dimensions, respectively, thereby realizing the construction of a high strain energy density (strong plasticity product) CoCrNi medium-entropy alloy.

[0018] To address the aforementioned technical problems, this invention proposes a method for preparing a biomimetic brick-and-mortar structure high strain energy density CoCrNi medium-entropy alloy, comprising the following steps:

[0019] Step 1) Take a bulk CoCrNi alloy with a density of not less than 99%, cold roll it, then anneal and water quench it to room temperature;

[0020] Step 2) High-speed rolling is used to perform multi-pass surface nano-sizing treatment on both sides of the annealed bulk CoCrNi alloy, thereby creating a biomimetic brick-and-mortar structure with gradient and layered grain sizes in two dimensions.

[0021] Furthermore, in the method for preparing the CoCrNi medium-entropy alloy described in this invention, wherein:

[0022] In step 1), the mass percentage range of Co, Cr and Ni in the bulk CoCrNi alloy is 32-34% / 32-34% / 32-34%, and the sum of the mass percentages is 100%.

[0023] In step 1), the total reduction of the bulk CoCrNi alloy during cold rolling is 30-50%; the alloy with a thickness of 1-3 mm after cold rolling is annealed at a temperature of 700-800℃ for 1-3 hours.

[0024] In step 2), alternating regions 1 and 2 are divided on both the upper and lower surfaces of the annealed bulk CoCrNi alloy. The process conditions for surface nano-processing using high-speed rolling are as follows: the high-speed rolling cutting head is a WC / Co cemented carbide ball, the rolling speed is 2000-2500 mm / min, the single-pass reduction is 1-10 μm, and oil lubrication is used during the processing. For region 1, the number of processing passes is N; for region 2, the number of processing passes is N+M; N = 1-4, M = 1-4; the number of regions 1 and 2 is greater than 2.

[0025] The single-pass reduction amount is the same in Region 1, and the single-pass reduction amount is the same in Region 2.

[0026] In step 2), alternating regions 1 and 2 are symmetrically distributed on the upper and lower surfaces of the annealed bulk CoCrNi alloy. The CoCrNi medium-entropy alloy obtained after high-speed rolling treatment includes an unevenly distributed gradient nanocrystalline layer on the upper and lower surfaces and a uniformly distributed coarse-grained layer between the upper and lower surfaces.

[0027] The biomimetic brick-and-mortar structure high strain energy density CoCrNi medium-entropy alloy provided by this invention has the following beneficial effects:

[0028] (1) Compared to the polarized mechanical properties of traditional homogeneous alloys, the biomimetic brick-and-mud structure CoCrNi medium-entropy alloy prepared in this invention exhibits a synergistic improvement in the seemingly contradictory properties of strength and tensile plasticity. This invention employs high-speed rolling technology to perform surface nano-sizing treatments on both sides of the alloy using different passes. High-speed rolling reduces grain size, and the brick region undergoes more processing passes than the mud region, resulting in higher strength. Furthermore, the grain size in the brick and mud regions exhibits a spatial gradient and layered structure. Along the thickness direction, the grain size shows a symmetrical gradient structure, while along the length direction, it exhibits an alternating layered structure of brick and mud. This dual heterogeneous structure gives the alloy a significant heterogeneous strengthening effect. In addition, the mutual constraint between the soft and hard regions of the brick and mud also helps alleviate strain localization and maintain high plastic deformation stability, thereby giving the alloy a high strain energy density (strength-plasticity product).

[0029] (2) This invention can prepare alloy plates with alternating transverse and longitudinal brick-mud structures of different sizes. Different heterogeneous strengthening effects can be achieved by changing the process parameters to prepare alloy plates with different sizes of brick-mud structures. The length and width of the brick-mud are determined by the distance of the alternating transverse and longitudinal movement of the rolling cutter head. The number of alternating layers of brick-mud can be changed by changing the processing distance. The thickness of the brick-mud is determined by the number of processing passes and the amount of reduction per pass. The more processing passes and the greater the reduction, the greater the thickness. The thickness of the brick-mud can be changed by changing the parameters.

[0030] (3) The process of this invention is simple and universal, and can be extended to other metal material processing fields. Attached Figure Description

[0031] Figure 1 This is a simplified schematic diagram illustrating the preparation method of the biomimetic brick-and-mortar structure CoCrNi medium-entropy alloy of the present invention.

[0032] Figure 2 for Figure 1 A simplified structural diagram of the biomimetic brick-mud structure CoCrNi medium-entropy alloy prepared by the method shown.

[0033] Figure 3 The tensile stress-strain curves are for Examples 1-6. Detailed Implementation

[0034] This invention proposes a method for preparing a biomimetic brick-and-mortar structure high strain energy density CoCrNi medium-entropy alloy, which mainly includes: pretreatment of CoCrNi bulk raw material alloy and surface nano-sizing treatment by high-speed rolling in different regions, ultimately obtaining the CoCrNi medium-entropy alloy. Figure 1As shown, when performing surface nano-sizing using high-speed rolling in different regions, alternating regions one and two are first defined on both the upper and lower surfaces of the annealed bulk CoCrNi alloy. Region one is defined as the "brick region," and region two as the "mud region." Then, using a rolling cutter, the "brick region" and "mud region" are respectively subjected to high-speed rolling with a covering effect according to the set region width, specified number of processing passes, and rolling process conditions. The final product is a biomimetic brick-mud structure high strain energy density CoCrNi medium-entropy alloy, as shown in the figure. Figure 2 As shown, the CoCrNi medium-entropy alloy comprises an upper and lower layer of unevenly distributed gradient nanocrystalline layers and a lower and lower layer of uniformly distributed coarse-grained layers; the grain size has a biomimetic brick-and-mortar structure with gradient structure and layered structure in two dimensions.

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to several embodiments. It should be understood that the embodiments described herein are merely illustrative and not intended to limit the invention. This invention can be implemented through various embodiments, and the scope of protection of this invention is not limited to the embodiments mentioned herein.

[0036] Example 1

[0037] The steps for preparing a biomimetic brick-mud structure high strain energy density CoCrNi medium-entropy alloy are as follows:

[0038] Step 1) Pretreatment of CoCrNi bulk alloy raw material:

[0039] Take a CoCrNi bulk alloy, wherein the mass percentage content of Co, Cr and Ni is: Co 33%, Cr 33% and Ni 34%; grind the bulk alloy flat, and then cold roll the alloy to reduce the total thickness by 30% through a two-roll cold rolling mill. The thickness of the alloy after cold rolling is 1 mm. Place the cold-rolled alloy in a vacuum furnace for annealing at 800℃ for 2 hours, and then water quench to room temperature.

[0040] Step 2) Surface nano-sizing is performed in sections using high-speed rolling to obtain a CoCrNi medium-entropy alloy:

[0041] The pretreated alloy was placed on a CNC machine tool and milled flat with a milling cutter. The alloy was divided into four corresponding regions on both the top and bottom (front and back) sides. Regions 1 and 3, spaced apart, were designated as brick regions, and regions 2 and 4, spaced apart, were designated as mud regions. The starting coordinates for machining the brick regions were (0, -3) and (0, -10), with widths of 3.5 mm and 3 mm, respectively. Each region was machined in three passes, with a cutter depth of 3 μm per pass. The starting coordinates for machining the mud regions were (0, 0) and (0, -6.5), with widths of 3 mm and 3.5 mm, respectively. Each region was machined in two passes, with a cutter depth of 5 μm per pass.

[0042] Turn on the machine tool and perform high-speed roll forming on the brick and mud area set on the front side. The roll forming speed is 2500 mm / min, the roll forming path is a straight reciprocating path and oil lubrication is used throughout the process.

[0043] The same processing method as described above for the brick and mud areas on the front side is repeated on the reverse side of the alloy, and the pre-designed alloy is thus produced. For example... Figure 2 As shown, the CoCrNi medium-entropy alloy obtained after high-speed rolling treatment includes two unevenly distributed gradient nanocrystalline layers on the top and bottom, and a uniformly distributed coarse-grained layer between the top and bottom layers.

[0044] Example 2

[0045] The steps for preparing a biomimetic brick-mud structure high strain energy density CoCrNi medium-entropy alloy are as follows:

[0046] Step 1) Pretreatment of CoCrNi bulk alloy raw material:

[0047] Take a CoCrNi bulk alloy, wherein the mass percentage content of Co, Cr and Ni is: Co 32%, Cr 34% and Ni 34%; grind the bulk alloy flat, and then cold roll the alloy to reduce the total thickness by 30% through a two-roll cold rolling mill, and the thickness of the cold-rolled alloy is 1.5 mm; place the cold-rolled alloy in a vacuum furnace for annealing at 800℃ for 2 hours, and then water quench to room temperature.

[0048] Step 2) Surface nano-sizing is performed in sections using high-speed rolling to obtain a CoCrNi medium-entropy alloy:

[0049] The pretreated alloy was placed on a CNC machine tool and its surface was milled flat with a milling cutter. Nine corresponding regions were divided on both the upper and lower (front and back) sides of the alloy. Regions 1, 3, 5, 7, and 9 were designated as brick regions, and regions 2, 4, 6, and 8 were designated as mud regions. The starting coordinates for the machining of the five brick regions were (0, 0), (0, -6), (0, -8), (0, -10), and (0, -14), with widths of 3 mm, 1 mm, 1 mm, 1 mm, and 3 mm, respectively. Each region was machined five times, with a cutter depth of 6 μm per pass. The starting coordinates for the machining of the four mud regions were (0, -3), (0, -7), (0, -9), and (0, -11), with widths of 3 mm, 1 mm, 1 mm, and 3 mm, respectively. Each region was machined four times, with a cutter depth of 2.5 μm per pass.

[0050] Turn on the machine tool and perform a covering roll forming process on the brick and mud area set on the front side. The roll forming speed is 2500 mm / min, the roll forming path is a straight reciprocating path and oil lubrication is used throughout the process.

[0051] Repeat the same processing method for the front brick and mud areas on the reverse side of the alloy, and the preset alloy is thus prepared.

[0052] Example 3

[0053] The steps for preparing a biomimetic brick-mud structure high strain energy density CoCrNi medium-entropy alloy are as follows:

[0054] Step 1) Pretreatment of CoCrNi bulk alloy raw material:

[0055] Take a CoCrNi bulk alloy, wherein the mass percentage content of Co, Cr and Ni is: Co 32%, Cr 34% and Ni 34%; grind the bulk alloy flat, and then cold roll the alloy to reduce the total thickness by 50% through a two-roll cold rolling mill, and the thickness of the cold-rolled alloy is 2mm; place the cold-rolled alloy in a vacuum furnace for annealing at a temperature of 700℃ and a holding time of 2h, and then water quench to room temperature.

[0056] Step 2) Surface nano-sizing is performed in sections using high-speed rolling to obtain a CoCrNi medium-entropy alloy:

[0057] The pretreated alloy was placed on a CNC machine tool and its surface was milled flat with a milling cutter. Five corresponding regions were divided on both the upper and lower (front and back) sides of the alloy. Regions 1, 3, and 5 were spaced apart as mud regions, and regions 2 and 4 were spaced apart as brick regions. The starting coordinates for the three mud regions were (0, 0), (0, -6), and (0, -10), with widths of 3mm, 1mm, and 3mm, respectively. Each region was machined once, with a cutter depth of 5μm per pass. The starting coordinates for the two brick regions were (0, -3) and (0, -7), with a width of 3mm. Each region was machined four times, with a cutter depth of 5μm per pass.

[0058] Turn on the machine tool and perform a covering roll forming process on the brick and mud area set on the front side. The roll forming speed is 2000 mm / min, the roll forming path is a straight reciprocating path and oil lubrication is used throughout the process.

[0059] Repeat the same processing method for the front brick and mud areas on the reverse side of the alloy, and the preset alloy is thus prepared.

[0060] Example 4

[0061] The steps for preparing a biomimetic brick-mud structure high strain energy density CoCrNi medium-entropy alloy are as follows:

[0062] Step 1) Pretreatment of CoCrNi bulk alloy raw material:

[0063] Take a CoCrNi bulk alloy, wherein the mass percentage content of Co, Cr and Ni is: Co 33%, Cr 34% and Ni 33%; grind the bulk alloy flat, and then cold roll the alloy to reduce the total thickness by 50% through a two-roll cold rolling mill, and the thickness of the cold-rolled alloy is 2mm; place the cold-rolled alloy in a vacuum furnace for annealing at 800℃ for 3h, and then water quench to room temperature.

[0064] Step 2) Surface nano-sizing is performed in sections using high-speed rolling to obtain a CoCrNi medium-entropy alloy:

[0065] The pretreated alloy was placed on a CNC machine tool and its surface was milled flat with a milling cutter. Five corresponding regions were divided on both the upper and lower (front and back) sides of the alloy. Regions 1, 3, and 5 were spaced apart as mud regions, and regions 2 and 4 were spaced apart as brick regions. The starting coordinates for the three mud regions were (0, 0), (0, -12), and (0, -20), with widths of 6 mm, 2 mm, and 6 mm, respectively. Each region was machined once, with a cutter depth of 5 μm per pass. The starting coordinates for the two brick regions were (0, -6) and (0, -14), with a width of 6 mm. Each region was machined five times, with a cutter depth of 8 μm per pass.

[0066] Turn on the machine tool and perform a covering roll forming process on the brick and mud area set on the front side. The roll forming speed is 2000 mm / min, the roll forming path is a straight reciprocating path and oil lubrication is used throughout the process.

[0067] Repeat the same processing method for the front brick and mud areas on the reverse side of the alloy, and the preset alloy is thus prepared.

[0068] Example 5

[0069] The steps for preparing a biomimetic brick-mud structure high strain energy density CoCrNi medium-entropy alloy are as follows:

[0070] Step 1) Pretreatment of CoCrNi bulk alloy raw material:

[0071] Take a CoCrNi bulk alloy, wherein the mass percentage content of Co, Cr and Ni is: Co 32.5%, Cr 33.5% and Ni 34%; grind the bulk alloy flat, and then cold roll the alloy to reduce the total thickness by 50% through a two-roll cold rolling mill, and the thickness of the cold-rolled alloy is 3mm; place the cold-rolled alloy in a vacuum furnace for annealing at a temperature of 700℃ and a holding time of 2h, and then water quench to room temperature.

[0072] Step 2) Surface nano-sizing is performed in sections using high-speed rolling to obtain a CoCrNi medium-entropy alloy:

[0073] The pretreated alloy was placed on a CNC machine tool and its surface was milled flat with a milling cutter. Five corresponding regions were divided on both the upper and lower (front and back) sides of the alloy. Regions 1, 3, and 5 were spaced apart as mud regions, and regions 2 and 4 were spaced apart as brick regions. The starting coordinates for the three mud regions were (0, 0), (0, -6), and (0, -10), with widths of 3mm, 1mm, and 3mm, respectively. Each region was machined once, with a cutter depth of 5μm per pass. The starting coordinates for the two brick regions were (0, -3) and (0, -7), with a width of 3mm. Each region was machined twice, with a cutter depth of 5μm per pass.

[0074] Turn on the machine tool and perform a covering roll forming process on the brick and mud area set on the front side. The roll forming speed is 2000 mm / min, the roll forming path is a straight reciprocating path and oil lubrication is used throughout the process.

[0075] Repeat the same processing method for the front brick and mud areas on the reverse side of the alloy, and the preset alloy is thus prepared.

[0076] Example 6

[0077] The steps for preparing a biomimetic brick-mud structure high strain energy density CoCrNi medium-entropy alloy are as follows:

[0078] Step 1) Pretreatment of CoCrNi bulk alloy raw material:

[0079] Take a CoCrNi bulk alloy, wherein the mass percentage content of Co, Cr and Ni is: Co 32%, Cr 34% and Ni 34%; grind the bulk alloy flat, and then cold roll the alloy to reduce the total thickness by 50% through a two-roll cold rolling mill, and the thickness of the cold-rolled alloy is 3mm; place the cold-rolled alloy in a vacuum furnace for annealing at 800℃ for 3h, and then water quench to room temperature.

[0080] Step 2) Surface nano-sizing is performed in sections using high-speed rolling to obtain a CoCrNi medium-entropy alloy:

[0081] The pretreated alloy was placed on a CNC machine tool and its surface was milled flat with a milling cutter. Seven corresponding regions were divided on both the upper and lower (front and back) sides of the alloy. Regions 1, 3, 5, and 7 were designated as brick regions, and regions 2, 4, and 6 were designated as mud regions. The starting coordinates for the four brick regions were (0, 0), (0, -3), (0, -7), and (0, -11), with widths of 2mm, 3mm, 4mm, and 2mm, respectively. Each region was machined in two passes, with a cutter depth of 8μm per pass. The starting coordinates for the three mud regions were (0, -2), (0, -6), and (0, -10), with a width of 1mm. Each region was machined in one pass, with a cutter depth of 8μm per pass.

[0082] Turn on the machine tool and perform a covering roll forming process on the brick and mud area set on the front side. The roll forming speed is 2000 mm / min, the roll forming path is a straight reciprocating path and oil lubrication is used throughout the process.

[0083] Repeat the same processing method for the front brick and mud areas on the reverse side of the alloy, and the preset alloy is thus prepared.

[0084] The following data are provided for comparison of four heterostructure-reinforced CoCrNi medium-entropy alloys to illustrate the high strain energy density of this invention. Among them:

[0085] Comparative Example 1: Using an equal-diameter angular channel extrusion and annealing process, a heterogeneous structure of nanotwinned HCP sheets and annealed twins is synergistically strengthened in CoCrNi medium-entropy alloy. [7] .

[0086] Comparative Example 2: Adding Al and Ti elements to a CoCrNi medium-entropy alloy resulted in a heterogeneous FCC matrix, spherical γ' precipitates, and a multi-scale heterogeneous structure with high number density of crystal defects. [8] .

[0087] Comparative Example 3: A monolayer of CoCrFeMnNi high-entropy alloy was deposited on a CoCrNi medium-entropy alloy using additive manufacturing technology, leveraging the synergistic strengthening effect of its heterogeneous structure and composition. [9] .

[0088] Comparative Example 4: CoCrNi was subjected to multiple low-temperature rolling passes until the thickness was reduced by approximately 90%. Before each rolling pass, the alloy was immersed in liquid nitrogen for 5 minutes, followed by annealing at 600°C for 20 minutes. This alloy exhibited a deformed substructure and recrystallized ultrafine grains.

[10] Heterogeneous structure.

[0089] Uniaxial tensile tests were conducted on Examples 1-6 using an INSTRON 68TM-500,000 strength testing machine. Figure 3 Its stress-strain curve is shown in Table 1.

[0090] Table 1 shows the tensile properties data of Examples 1-6 and Comparative Examples 1-4.

[0091] Example Yield strength (MPa) Tensile strength (MPa) Plasticity (%) Strain energy density Density % Example 1 880 1050 27.4 241 99.2 Example 2 922 1060 20.0 184 99.0 Example 3 910 1058 32.3 294 99.5 Example 4 830 982 28.8 239 99.3 Example 5 839 1087 38.9 326 99.5 Example 6 914 1097 32.1 293 99.4 Comparative Example 1 829 841 19.0 158 - Comparative Example 2 1200 1600 13.5 162 - Comparative Example 3 1109 1290 20.0 222 - Comparative Example 4 1080 1224 17.0 184 -

[0092] As shown in Table 1, the overall effect of this invention is superior to that of the literature on heterostructure-strengthened CoCrNi medium-entropy alloys. The raw material alloy needs a density of not less than 99% because density affects the alloy's properties. Too low a density indicates high porosity and uneven microstructure distribution, which negatively impacts performance. Different processing parameters in the brick-mud region also affect the alloy's properties. More processing passes and greater reduction result in higher strength but also decreased plasticity. The brick region requires 1-4 more processing passes than the mud region because a large strength difference between the two regions cannot be excessively pursued. Although a greater strength difference leads to a more significant heterostructure strengthening effect, increased processing passes and reduction may also result in more surface microcracks, causing faster crack propagation during tensile testing and premature fracture.

[0093] Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art, under the guidance of the present invention, can obviously make simple changes or equivalent substitutions to the technical solutions without departing from the spirit of the present invention, and these changes are all within the protection scope of the present invention.

Claims

1. A method for preparing a high strain energy density CoCrNi medium-entropy alloy with a biomimetic brick clay structure, characterized in that, The method comprises the following steps: Step 1) taking a bulk CoCrNi alloy with a density of not less than 99%, cold-rolling the bulk CoCrNi alloy, and then annealing and water quenching to room temperature; Step 2) performing multi-pass surface nanocrystallization treatment on the front and back surfaces of the treated bulk CoCrNi alloy by high-speed rolling, so that the grain size has gradient structure and layered structure in two-dimensional space respectively, thereby forming a biomimetic brick structure; In step 1), the mass percentage of Co, Cr and Ni in the bulk CoCrNi alloy ranges from 32% to 34%, from 32% to 34% and from 32% to 34% respectively, and the sum of the mass percentages is 100%; the total reduction of the cold-rolled bulk CoCrNi alloy is 30% to 50%; the cold-rolled alloy with a thickness of 1-3 mm is annealed at a temperature of 700-800 DEG C for 1-3 h; In step 2), the upper and lower surfaces of the treated bulk CoCrNi alloy are divided into alternating region I and region II, and the region I and region II are symmetrical; In step 2), the process conditions of surface nanocrystallization treatment by high-speed rolling are as follows: the machining tool bit of high-speed rolling is WC / Co hard alloy ball, the rolling speed is 2000-2500 mm / min, the single-pass reduction is 1-10 μm, and oil lubrication is used during the machining process; for region I, the machining passes are N; for region II, the machining passes are N+M; N=1-4, M=1-4; the number of region I and region II is greater than 2; the single-pass reduction of region I is the same, and the single-pass reduction of region II is the same.

2. The method of producing a CoCrNi medium-entropy alloy according to claim 1, characterized in that, In step 2), the high-speed rolling treatment obtains a CoCrNi entropy alloy including two layers of gradient nanocrystalline layers with uneven distribution and two layers of coarse crystal layers with uniform distribution.

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