CoCrNi-based multi-principal-element alloy with adjustable strength and plasticity and preparation method of CoCrNi-based multi-principal-element alloy

Abstract

The invention provides a CoCrNi-based multi-principal-element alloy with adjustable strength and plasticity and a preparation method thereof.The CoCrNi-based multi-principal-element alloy comprises, by atomic percent, 32%-36% of Co, 30%-34% of Cr, 28%-32% of Ni and 2%-6% of X. X comprises at least one of B, C, Al, Si, Sc, Ti, V, Mn, Fe, Cu, Zr, Nb, Mo, Hf, Ta, W and Re; the CoCrNi-based multi-principal-element alloy takes an FCC (Fluid Catalytic Cracking) structure as a matrix and contains nanoscale precipitated phases which are distributed in a dispersed manner. According to the method, an alloy master ingot is obtained through vacuum arc melting, then an alloy plate is prepared through a vacuum suction casting process, and on the basis, the microscopic structure and the mechanical property of the alloy are regulated and controlled through combination of element doping, liquid nitrogen cold rolling and an annealing process, so that the alloy with different matched strength and plasticity is obtained.

Description

Technical Field

[0001] This invention relates to the field of high-entropy alloy materials technology, specifically to a CoCrNi-based multi-principal-element alloy with adjustable strength and plasticity and its preparation method. Background Technology

[0002] CoCrNi-based alloys have attracted widespread attention due to their excellent low-temperature toughness and ductility, showing broad application prospects in aerospace, marine engineering, energy equipment, and high-end manufacturing. However, these alloys generally suffer from low yield strength, making it difficult to meet the strength and reliability requirements of structural materials under extreme environments. This presents a contradiction between strength and plasticity, severely restricting their engineering applications. Research has found that by introducing refractory or light alloying elements into the CoCrNi matrix to form a multiphase composite structure, and combining this with hot working and heat treatment processes, the mechanical properties of the alloy can be significantly improved, achieving a balance between strength and plasticity. Therefore, composition optimization and process control of CoCrNi-based multi-principal element alloys are particularly important.

[0003] Currently, domestic and international research institutions and enterprises generally adopt methods such as modifying alloy composition design, optimizing heat treatment processes, introducing cold rolling deformation, and multi-scale microstructure control to improve the mechanical properties of CoCrNi-based alloys, and have prepared a series of high-entropy or medium-entropy alloys with excellent properties. Although these methods have improved the balance between strength and plasticity to some extent, there are still many insurmountable problems: First, the crystal structure and the formation of the second phase are difficult to control precisely, resulting in unstable strengthening effects; second, obtaining the strengthening phase often requires relatively complex processing technology, which is not conducive to mass production; third, some methods are prone to causing risks such as inhomogeneous alloy microstructure, uncontrolled phase distribution, and non-reproducible mechanical properties, reducing the reliability and stability of the material.

[0004] Therefore, there is an urgent need for a new method to achieve synergistic regulation of alloy microstructure and properties, thereby breaking through the bottleneck of the mutual exclusion of strength and plasticity and improving the overall service performance of CoCrNi-based alloys. Summary of the Invention

[0005] In view of the technical problems existing in the background art, the present invention provides a CoCrNi-based multi-principal element alloy with adjustable strength and plasticity and its preparation method, aiming to solve the technical problems of difficulty in balancing strength and plasticity and complex processing technology of CoCrNi-based alloy materials in the prior art.

[0006] In a first aspect, the present invention provides a CoCrNi-based multi-principal alloy with adjustable strength and plasticity, comprising the following components by atomic percentage: 32%~36% Co, 30%~34% Cr, 28%~32% Ni and 2%~6% X, wherein X includes at least one of B, C, Al, Si, Sc, Ti, V, Mn, Fe, Cu, Zr, Nb, Mo, Hf, Ta, W and Re; the CoCrNi-based multi-principal alloy has an FCC structure as the matrix and contains dispersed nanoscale precipitates.

[0007] Preferably, the composition of the CoCrNi-based multi-principal element alloy, based on atomic percentage, is: Co 34 Cr 32 Ni 30 Al4 or Co 34 Cr 32 Ni 30 Ti4 or Co 34 Cr 32 Ni 30 Nb4 or Co 34 Cr 32 Ni 30 Ta or Co 34 Cr 32 Ni 30 W4.

[0008] Secondly, the present invention provides a method for preparing a CoCrNi-based multi-principal element alloy with adjustable strength and plasticity, comprising the following steps: S1. Weigh out the elemental metals Co, Cr, Ni and dopant X respectively, mix them in proportion and then melt them in a vacuum electric arc furnace to obtain alloy ingots. S2. Obtain as-cast alloy plates from alloy ingots by vacuum casting. S3. Perform homogenization annealing on the cast alloy sheet; S4. The alloy sheet after homogenization annealing is subjected to cold rolling deformation treatment with a cumulative deformation of 50% to 85% in multiple passes under liquid nitrogen cooling conditions. S5. The cold-rolled and deformed sample is subjected to recrystallization annealing and aging treatment to obtain CoCrNi-based multi-principal element alloy.

[0009] Preferably, in step S1, the purity of the elemental metal raw material is ≥99.99%; the elemental metal raw material undergoes oxide layer removal treatment before smelting.

[0010] Preferably, in step S1, the vacuum arc melting specifically involves: evacuating the arc melting furnace, filling it with high-purity argon gas for protection, and then reversing and melting it 5-6 times under the protection of high-purity argon gas to obtain an alloy ingot.

[0011] Preferably, the vacuum arc melting current is 200~400A, and the vacuum arc melting time is 60~80s / cycle.

[0012] Preferably, in step S3, the homogenization annealing treatment is carried out at a temperature of 1373~1573K for 1~2h.

[0013] Preferably, in step S4, the deformation amount per pass in the cold rolling deformation process is ≤1%, and the rolling speed is 10~20m / min.

[0014] Preferably, in step S5, the recrystallization annealing treatment is carried out at a temperature of 1073~1273K for a time of 0.5~1h.

[0015] Preferably, in step S5, the aging treatment temperature is 873~1073K and the time is 4~6h.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention prepares a high-strength and high-toughness CoCrNi-based multi-principal element alloy by synergistically controlling the microstructure through "element doping + liquid nitrogen cold rolling + annealing". The prepared alloy material has the advantages of high microstructure controllability, good mechanical property stability and high repeatability, and exhibits excellent strength and plasticity combination, which has important industrial application prospects.

[0017] (2) The alloy material preparation method provided by this invention is simple, highly applicable, and scalable. It can obtain multi-scale heterogeneous structures without relying on complex thermomechanical treatment and extreme process conditions, thereby improving strength while maintaining the toughness of the alloy matrix, achieving flexible control of strength and plasticity, low production cost, and large-scale industrialization potential. Furthermore, by controlling the type of doping element, the amount of cold rolling deformation, and the annealing parameters, the type, morphology, and distribution of the second phase in the alloy can be effectively controlled, thereby achieving adjustable targets for strength and plasticity. For example, under W doping conditions, the tensile strength of the alloy can reach 1074 MPa, and the elongation is maintained at 54.5%; under Ti doping conditions, the tensile strength exceeds 1400 MPa; while Al doping helps to stabilize the FCC matrix and maintain excellent ductility. Attached Figure Description

[0018] Figure 1 The XRD patterns of the alloy materials prepared in Comparative Examples 1 and 4 of this invention are shown. Figure 2 SEM images of the alloy materials prepared in Comparative Examples 1 and 4 of the present invention are shown, wherein (a) is Comparative Example 1; (b~r) are Comparative Examples 4. Figure 3The Vickers hardness diagrams are for the alloy materials prepared in Comparative Examples 1 and 4 of this invention, wherein (a) they are arranged according to increasing atomic number and (b) they are arranged according to increasing atomic radius. Figure 4 The above are XRD patterns of the alloy materials obtained in Comparative Example 3 and Examples 1-5 of this invention. Figure 5 SEM images of the alloy materials prepared in Comparative Example 3 and Example 1 of the present invention are shown, where (a,b) are Comparative Example 3 and (c,d) are Example 1. Figure 6 Here is a SEM image of the alloy material obtained in Example 2 of this invention; Figure 7 The image shown is the EDS diagram of the alloy material obtained in Example 2 of this invention. Figure 8 Here is a SEM image of the alloy material obtained in Example 3 of this invention; Figure 9 Here is a SEM image of the alloy material obtained in Example 4 of this invention; Figure 10 Here is a SEM image of the alloy material obtained in Example 5 of this invention; Figure 11 This is a comparison chart of the tensile properties of the alloy materials obtained in Comparative Example 3 and Examples 1-5 of the present invention; Figure 12 The macroscopic morphology of the alloy material prepared in Comparative Example 5 of the present invention is shown, wherein (a) is a single-pass deformation amount > 10%; and (b) is a single-pass deformation amount > 20%. Detailed Implementation

[0019] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0020] To address the technical problem of balancing strength and plasticity in existing CoCrNi-based alloy materials, this invention provides a CoCrNi-based multi-principal element alloy with controllable strength and plasticity, and its preparation method. This method achieves synergistic effects of solid solution strengthening, precipitation strengthening, and strain hardening by inducing lattice distortion and second-phase formation through element doping, combined with heterostructure control induced by cold rolling annealing. Ultimately, this results in controllable strength and plasticity.

[0021] In a first aspect, embodiments of the present invention provide a CoCrNi-based multi-principal alloy with adjustable strength and plasticity, comprising the following components by atomic percentage: 32%~36% Co, 30%~34% Cr, 28%~32% Ni and 2%~6% X, wherein X includes at least one of B, C, Al, Si, Sc, Ti, V, Mn, Fe, Cu, Zr, Nb, Mo, Hf, Ta, W and Re; the CoCrNi-based multi-principal alloy has an FCC structure as the matrix and contains dispersed nanoscale precipitates.

[0022] Furthermore, in some embodiments, the composition of the CoCrNi-based multi-principal element alloy, based on atomic percentage, is: Co 34 Cr 32 Ni 30 Al4 or Co 34 Cr 32 Ni 30 Ti4 or Co 34 Cr 32 Ni 30 Nb4 or Co 34 Cr 32 Ni 30 Ta or Co 34 Cr 32 Ni 30 W4.

[0023] Secondly, embodiments of the present invention provide a method for preparing a CoCrNi-based multi-principal-element alloy with adjustable strength and plasticity, comprising the following steps: S1. Weigh out the elemental metals Co, Cr, Ni and dopant X respectively, mix them in proportion and then melt them in a vacuum electric arc furnace to obtain alloy ingots. S2. Obtain as-cast alloy plates from alloy ingots by vacuum casting. S3. Perform homogenization annealing on the cast alloy sheet; S4. The alloy sheet after homogenization annealing is subjected to cold rolling deformation treatment with a cumulative deformation of 50% to 85% in multiple passes under liquid nitrogen cooling conditions. S5. The cold-rolled and deformed sample is subjected to recrystallization annealing and aging treatment to obtain CoCrNi-based multi-principal element alloy.

[0024] In the technical solution of this invention, the method first obtains an alloy master ingot through vacuum arc melting, then prepares CoCrNi-based multi-principal element alloy plates using vacuum casting. Based on this, the microstructure and mechanical properties of the alloy are controlled by combining element doping with liquid nitrogen cold rolling and annealing processes. Compared with conventional cold rolling processes used in the prior art, the liquid nitrogen cold rolling used in this invention has significant advantages. When liquid nitrogen cold rolling deformation is performed, the deformation temperature is significantly reduced (approximately 77 K), which effectively suppresses dynamic recovery and dislocation annihilation behavior in the alloy, allowing the alloy to accumulate higher strain energy and dislocation density during deformation, while simultaneously inducing the formation of high-density stacking faults and deformation twin structures. These substructural features formed by low-temperature deformation can provide numerous nucleation sites and diffusion channels during subsequent recrystallization annealing and aging processes, thereby promoting the dispersed precipitation of the second phase and grain refinement. After appropriate recrystallization annealing and aging treatment, liquid nitrogen cold-rolled samples can simultaneously obtain a stable FCC matrix and uniformly dispersed nanoscale precipitates, forming a multi-scale heterostructure composed of fine-grained regions, twinned regions, and precipitation-strengthened regions. This microstructure significantly improves the synergistic control ability between dislocations, grain boundaries, and precipitates, achieving a synergistic improvement in strength and plasticity. In contrast, during ordinary cold rolling, due to the higher deformation temperature, the dynamic recovery effect is significant, the dislocation density decreases, leading to coarsening of the subsequent recrystallization structure and a reduction in the number of precipitates, making it difficult to form a stable and refined heterostructure. Furthermore, by rationally selecting doping elements (such as W, Ti, Al, Nb, Ta, etc.) and controlling the amount of cold rolling deformation and annealing temperature, various microstructures such as single-phase FCC, FCC+BCC, and FCC+intermetallic compounds can be achieved, thereby obtaining alloys with different strength and plasticity matching.

[0025] Furthermore, in some embodiments, in step S1, the purity of the elemental metal raw material is ≥99.99%; the elemental metal raw material undergoes oxide layer removal treatment before smelting.

[0026] Furthermore, in some embodiments, in step S1, vacuum arc melting specifically involves: evacuating the arc melting furnace, filling it with high-purity argon gas for protection, and then reversing and melting it 5-6 times under the protection of high-purity argon gas to obtain an alloy ingot.

[0027] Furthermore, in some embodiments, the current of vacuum arc melting is 200~400A, and the vacuum arc melting time is 60~80s / cycle.

[0028] Furthermore, in some embodiments, in step S3, the homogenization annealing treatment is carried out at a temperature of 1373~1573K for a time of 1~2h.

[0029] In the technical solution of this invention embodiment, homogenization annealing is used to eliminate compositional segregation, which can effectively reduce microsegregation and residual stress in the cast alloy, providing a good microstructure basis for subsequent cold rolling deformation and heat treatment.

[0030] Furthermore, in some embodiments, in step S4, the deformation amount per pass in the cold rolling deformation process is ≤1%, and the rolling speed is 10~20m / min.

[0031] In the technical solution of this invention embodiment, the cold rolling deformation treatment under liquid nitrogen cooling conditions adopts a multi-pass cumulative deformation method, with the deformation amount of each pass controlled at ≤1%, and the cumulative total deformation amount being 50%~85%. This method can balance both high strain accumulation and microstructure stability, ensuring deformation integrity while avoiding early fracture caused by over-processing. This invention does not limit the rolling path and can conventionally select rolling methods such as segmented rolling and cross rolling.

[0032] Furthermore, in some embodiments, in step S5, the recrystallization annealing treatment is carried out at a temperature of 1073~1273K for a time of 0.5~1h.

[0033] Furthermore, in some embodiments, in step S5, the aging treatment temperature is 873~1073K and the time is 4~6h.

[0034] In the technical solution of this invention embodiment, after appropriate recrystallization annealing and aging treatment, the liquid nitrogen cold-rolled sample can simultaneously obtain a stable FCC matrix and uniformly dispersed nanoscale precipitates, forming a multi-scale heterostructure composed of fine-grained regions, twinned regions, and precipitation-strengthened regions. This microstructure significantly improves the synergistic control capability between dislocations, grain boundaries, and precipitates, achieving a synergistic improvement in strength and plasticity.

[0035] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0036] In the following examples, the purity of each elemental metal raw material is ≥99.99%.

[0037] Example 1 (Al microalloying and liquid nitrogen cold rolling-recrystallization-aging treatment) Co 34 Cr 32 Ni 30 The preparation method of Al4 (at.%) alloy material, the specific steps are as follows: S1. Ingredients: Treat the surface of each elemental metal raw material to remove the oxide layer, and ultrasonically clean each raw material with acetone / deionized water (1:1) for 10 minutes, and blow dry; mix according to the ratio Co:Cr:Ni:Al=34:32:30:4 (at.%), calculate the mass of each with a total mass of 50g and weigh them.

[0038] Preparation of S2 alloy ingot: Using vacuum arc melting, the various elemental metal raw materials of S1 were placed in a water-cooled copper crucible, and a vacuum of 3.5 × 10⁻⁶ was applied. -4 Pa, filled with high-purity Ar to a protective atmosphere of 0.6 atm; under the protection of high-purity argon, the alloy ingot was tumbled and melted 6 times (360A, 70s / time) to obtain a uniform alloy ingot.

[0039] S3. Cast Plate and Homogenization: The alloy ingot is cut into blocks and melted in a suction casting copper mold. The melted blocks are then injected into a water-cooled copper mold using a vacuum casting method, at approximately 5 × 10⁻⁶ mm. 4 Rapid solidification at a cooling rate of K / s yielded a cast plate with dimensions of 10mm × 10mm × 40mm.

[0040] S4. Liquid nitrogen cold rolling-recrystallization-aging treatment: The sample was homogenized and annealed at 1473K for 2 hours (Ar protection), then water-quenched to room temperature. The sample was then immersed in liquid nitrogen for 5 minutes. Afterward, the immersed T1 sample was removed and rolled at a speed of 10-20 m / min under liquid nitrogen cooling conditions, with a cumulative deformation of 80% (single pass ≤1%). It was then recrystallized and annealed at 1173K for 1 hour, followed by air cooling. Finally, it was aged at 973K for 4 hours, followed by air cooling, to obtain Co. 34 Cr 32 Ni 30 Al4 (at.%) alloy material, denoted as sample T1.

[0041] This embodiment achieves high ductility by stabilizing the FCC matrix with Al and combining it with the preparation process.

[0042] Example 2 (Ti microalloying and liquid nitrogen cold rolling-recrystallization-aging treatment) Co 34 Cr 32 Ni 30 The preparation method of Ti4 (at.%) alloy material is the same as that in Example 1, except that in step S1, metallic Al is replaced with metallic Ti, and the materials are mixed in the ratio Co:Cr:Ni:Ti = 34:32:30:4 (at.%). The mass of each component is calculated and weighed based on a total mass of 50g. The final product is Co. 34 Cr 32 Ni 30 Ti4 (at.%) alloy material, denoted as sample T2.

[0043] In this embodiment, the strength is improved by stabilizing the FCC matrix with Ti and forming a nano-precipitated phase through a preparation process.

[0044] Example 3 (Nb microalloying and liquid nitrogen cold rolling-recrystallization-aging treatment) Co 34 Cr 32 Ni 30 The preparation method of Nb4 (at.%) alloy material is the same as that in Example 1, except that in step S1, metallic Al is replaced with metallic Nb, and the alloy is prepared according to the ratio Co:Cr:Ni:Nb = 34:32:30:4 (at.%). The mass of each alloy is calculated and weighed based on a total mass of 50g. The final product is Co. 34 Cr 32 Ni 30 Nb4 (at.%) alloy material, denoted as sample T3.

[0045] This embodiment achieves an increase in yield strength by introducing Nb and using a suitable preparation process to form fine and stable intermetallic compounds / Laves-like precipitation.

[0046] Example 4 (Ta microalloying and liquid nitrogen cold rolling-recrystallization-aging treatment) Co 34 Cr 32 Ni 30 The preparation method of Ta4 (at.%) alloy material is the same as that in Example 1, except that in step S1, metallic Al is replaced with metallic Ta, and the materials are mixed in the ratio Co:Cr:Ni:Ta = 34:32:30:4 (at.%). The mass of each component is calculated and weighed based on a total mass of 50g. The final product is Co. 34 Cr 32 Ni 30 Ta4 (at.%) alloy material, denoted as sample T4.

[0047] This embodiment achieves an increase in yield strength by introducing Ta and using a preparation process to form a non-uniform precipitate in the shear band.

[0048] Example 5 (W microalloying and liquid nitrogen cold rolling-recrystallization-aging treatment) Co 34 Cr 32 Ni 30 The preparation method of W4 (at.%) alloy material is the same as that in Example 1, except that in step S1, metallic Al is replaced with metallic W, and the alloy is prepared according to the ratio Co:Cr:Ni:W = 34:32:30:4 (at.%). The mass of each alloy is calculated and weighed based on a total mass of 50g. The final product is Co.34 Cr 32 Ni 30 W4 (at.%) alloy material, denoted as sample T5.

[0049] In this embodiment, good strength and plasticity are obtained by using W to stabilize the FCC matrix and in conjunction with the preparation process.

[0050] Comparative Example 1 (undoped, without liquid nitrogen cold rolling-recrystallization-aging treatment) A traditional method for preparing CoCrNi alloy, the specific steps of which are as follows: S1. Ingredients: Treat the surface of each elemental metal raw material, remove the oxide layer, and ultrasonically clean each raw material with acetone / deionized water (1:1) for 10 minutes, blow dry, and mix according to the ratio of Co:Cr:Ni=1:1:1 (at.%). Calculate the mass of each raw material with a total mass of 50g and weigh them.

[0051] S2. Preparation of alloy ingots: Same as in Example 1; S3. Preparation of cast plate: Same as in Example 1, a CoCrNi cast plate with dimensions of 10mm×10mm×40mm was obtained, denoted as sample A1, without cold rolling-recrystallization-aging treatment.

[0052] Comparative Example 2 (undoped, subjected to cold rolling-recrystallization-aging treatment) A method for preparing a CoCrNi alloy, the specific steps of which are as follows: S1. Ingredients: Treat the surface of each elemental metal raw material, remove the oxide layer, and ultrasonically clean each raw material with acetone / deionized water (1:1) for 10 min, blow dry, and mix according to the ratio of Co:Cr:Ni=1:1:1 (at.%). Calculate the mass of each raw material with a total mass of 50g and weigh them.

[0053] S2. Preparation of alloy ingots: Same as in Example 1.

[0054] S3. Preparation of as-cast plate: Same as in Example 1, a CoCrNi as-cast plate with dimensions of 10 mm × 10 mm × 40 mm was obtained.

[0055] S4. Cold rolling-recrystallization-aging treatment: The sample was homogenized and annealed at 1473K for 2 hours (Ar protection), water-quenched to room temperature, and then subjected to multi-pass rolling at room temperature with a cumulative deformation of 80% (single pass ≤1%) at a rolling speed of 10~20m / min. Afterwards, it was recrystallized and annealed at 1173K for 1 hour, followed by air cooling; then aged at 973K for 4 hours, followed by air cooling, to obtain the CoCrNi alloy material, denoted as sample A2. Comparative Example 3 (undoped, subjected to liquid nitrogen cold rolling-recrystallization-aging treatment) A method for preparing a CoCrNi alloy, the specific steps of which are as follows: S1. Ingredients: Treat the surface of each elemental metal raw material, remove the oxide layer, and ultrasonically clean each raw material with acetone / deionized water (1:1) for 10 min, blow dry, and mix according to the ratio of Co:Cr:Ni = 1:1:1 (at.%). Calculate the mass of each raw material with a total mass of 50 g and weigh them.

[0056] S2. Preparation of alloy ingots: Same as in Example 1.

[0057] S3. Preparation of as-cast plate: Same as in Example 1, a CoCrNi as-cast plate with dimensions of 10mm×10mm×40mm was obtained.

[0058] S4. Liquid nitrogen cold rolling-recrystallization-aging treatment: Same as in Example 1. The final CoCrNi alloy material was obtained, denoted as Sample B1.

[0059] Comparative Example 4 (doped, but without liquid nitrogen cold rolling-recrystallization-aging treatment) A method for preparing a CoCrNi-based multi-principal element alloy (example alloy is Co). 34 Cr 32 Ni 30 X4 (at.%), where X is one of B, C, Al, Si, Sc, Ti, V, Mn, Fe, Cu, Zr, Nb, Mo, Hf, Ta, W, and Re), and the specific steps are as follows: S1. Ingredients: Treat the surface of each elemental metal raw material to remove the oxide layer, and ultrasonically clean each raw material with acetone / deionized water (1:1) for 10 min, then blow dry. Mix according to the ratio Co:Cr:Ni:X = 34:32:30:4 (at.%), calculate the mass of each raw material with a total mass of 50g, and weigh them.

[0060] Preparation of S2 alloy ingot: Vacuum arc melting was used. The raw material for S1 was placed in a water-cooled copper crucible, and a vacuum of 3.5 × 10⁻⁶ was applied. -4 Pa, filled with high-purity Ar to a protective atmosphere of 0.6 atm; under the protection of high-purity argon, the alloy ingot was tumbled and melted 6 times (360A, 70s / time) to obtain a uniform alloy ingot.

[0061] S3. Preparation of as-cast plate: The alloy ingot is cut into blocks and placed in a suction casting copper mold for melting. The melt is then injected into a water-cooled copper mold using a vacuum suction casting method, at approximately 5 × 10⁻⁶ mm. 4 Rapid solidification at a cooling rate of K / s yielded a Co sample with dimensions of 10mm × 10mm × 40mm. 34 Cr 32 Ni 30X4 (X is one of B, C, Al, Si, Sc, Ti, V, Mn, Fe, Cu, Zr, Nb, Mo, Hf, Ta, W, and Re) (at.%) cast plates were directly cooled without liquid nitrogen cold rolling-recrystallization-aging treatment. The resulting alloy materials were designated as samples C1-C17.

[0062] Comparative Example 5 (Nb microalloying and large deformation liquid nitrogen cold rolling) Co 34 Cr 32 Ni 30 The preparation method of Nb4 (at.%) alloy material differs from Example 3 in that the liquid nitrogen cold rolling in step S4 is large deformation liquid nitrogen cold rolling: the sample is homogenized and annealed at 1473K for 2 hours (Ar protection), water-quenched to room temperature, and then immersed in liquid nitrogen for 5 minutes. Afterward, the immersed sample is removed and subjected to large deformation liquid nitrogen cold rolling (single pass >10% and single pass >20%) under liquid nitrogen cooling conditions, with a rolling speed of 10~20 m / min. The remaining step parameters are the same as in Example 3. The final obtained Co 34 Cr 32 Ni 30 Nb4 (at.%) alloy materials, denoted as samples D1 and D2.

[0063] Performance testing The microstructure and mechanical properties of the CoCrNi-based multi-principal element alloy samples prepared in Examples 1-5 and Comparative Examples 1-5 were systematically characterized and compared. The results are discussed below: First, XRD and SEM analyses were performed on the CoCrNi-based multi-principal element alloy samples prepared in Comparative Examples 1 and 4, such as... Figure 1 and Figure 2 As shown, the addition of different elements leads to the formation of a second phase, but the FCC phase always exists, which ensures the high plasticity of the multi-principal element alloy. With the addition of different elements, it can be observed that the alloy changes from a single-phase FCC structure to FCC+BCC and FCC+other intermetallic compounds. This difference in phase composition and the existence of heterogeneous structures are the main reasons affecting the Vickers hardness and tensile properties of the alloy. The microhardness of Comparative Example 1 and Comparative Example 4 are shown in Table 1 and... Figure 3 As shown, it can be seen that Vickers hardness is significantly correlated with the addition of elements. For the same period, Vickers hardness gradually decreases with increasing atomic number; for the same group, Vickers hardness gradually increases with increasing atomic number; and with increasing atomic radius, Vickers hardness shows a gradual increasing trend, which is in good agreement with the lattice distortion theory of multi-principal element alloys.

[0064] Table 1

[0065] To determine Co 34 Cr 32 Ni 30 The phase composition of the X4(at.%) (X = elements such as Al, Ti, Nb, Ta and W, at.%) alloy system after the same cold rolling and heat treatment processes was analyzed by XRD for different multi-principal element alloys after liquid nitrogen cold rolling, recrystallization annealing and aging treatment. Figure 4 The XRD curves of the alloy systems in Comparative Example 2 (B1) and Examples 1-5 (T1-T5) are shown. It can be seen that alloy B1, after liquid nitrogen cold rolling, recrystallization annealing, and aging, exhibits a single-phase FCC crystal structure. As shown in alloy T1, even after adding Al, the multi-principal element alloy still maintains a single-phase FCC crystal structure. Figure 4 As can be seen in (b), the atomic radius of Al is larger than that of Co, Cr, and Ni (r). Al =1.43Å, r Co =1.25Å, r Cr =1.24Å and r Ni =1.30Å), therefore lattice distortion occurs, leading to an increase in the lattice constant of FCC; similar to alloy T1, alloys T2 and T3 show that the addition of Ti and Nb elements causes lattice distortion in FCC. Figure 4 (b) It can be seen that, since Ti and Al have similar atomic radii, alloys T2 and T3 have similar lattice constants; from Figure 4 (a) It can be seen that T4 and T5 indicate that with the addition of Ta and W elements, other diffraction peaks appeared around FCC, which were found to be the Laves phase after comparison. Figure 4 (b) The lattice parameters of T4 and T5 also increase. This phenomenon can be explained by the fact that Ta and W elements have larger atomic radii, while Co, Cr and Ni elements have relatively smaller radii. When dissolved in CoCrNi solid solution, lattice distortion occurs, leading to an increase in lattice parameters.

[0066] To further analyze the influence of liquid nitrogen cold rolling-recrystallization annealing-aging treatment on the microstructure of the alloy, detailed SEM analysis was performed on alloy samples B1, T1, T2, T3, T4, and T5. Figure 5 It can be seen that both the B1 alloy prepared in Comparative Example 3 and the T1 alloy prepared in Example 1 exhibit a fully recrystallized grain structure with a single, uniform microstructure, which is considered to be the FCC phase, and the overall structure presents as coarse equiaxed crystals. Figure 5 (b) and Figure 5 (d) The magnified image clearly shows that the annealed alloy has a large number of twins. Figure 6 and Figure 7 The microstructure and EDS spectrum of the T2 alloy prepared in Example 2 show that the alloy exhibits a distinct heterostructure, which is significantly different from the B1 and T1 alloys. Figure 6 (a) It can be seen that the T2 alloy has a heterogeneous structure combining coarse and fine grains. From Figure 6 As can be seen from (b), 6(c), and 6(d), the addition of Ti leads to the appearance of precipitates and lath-like structures in the alloy, possibly indicating a Ti-Ni enriched phase. In the T2 alloy, the heterostructure is achieved through thermomechanical treatment and precipitation. The microstructure of the cold-rolled sample exhibits multiple large deformation bands, as well as a small number of micro-bands and shear bands. The formation of large deformation bands and micro-bands under cold rolling conditions leads to the formation of heterostructures after annealing. The large deformation bands correspond to... Figure 6 In (a), the coarse-grained structure corresponds to the fine-grained structure in the micro-deformation zone. After annealing, due to the high dislocation density, recrystallized grains and precipitates first nucleate in the shear zone, while the large deformation zone remains in a recovery state. As the annealing time increases, recrystallization and grain growth occur in the large deformation zone, while the presence of precipitates limits the further growth of the initially recrystallized grains through a pinning effect. Figure 7 for Figure 6 (b) shows the EDS surface scan of the area within the red box. The image reveals an uneven distribution of elements within the T2 alloy. Figure 6 The black precipitates are Ti-rich phases. This is due to the unique composition of multi-principal alloy elements, which easily leads to compositional segregation during heat treatment, forming precipitated phases and thus altering the spatial distribution of the entire multi-principal alloy elements.

[0067] Figure 8 The microstructure of the T3 alloy prepared in Example 3 is shown. Figure 8 As shown, different precipitates of different sizes formed in the alloy after annealing. Figure 8 The magnified image in (b) shows a large number of nanoparticles precipitated in the alloy. To further determine the phase composition of the precipitated phase, as shown in Table 2, [the following was performed]. Figure 8 (b) EDS spot scan analysis was performed on different regions. It can be seen that both the micron-sized and nano-sized precipitates are Nb-rich phases, thus confirming that the precipitates are composed of the Laves phase. The microstructure of the T4 alloy prepared in Example 4 is as follows: Figure 9 As shown in Table 3, the Laves and FCC phases grow alternately, forming a heterostructure. From... Figure 9 (a) It can be seen that the alloy has a coarse-grained and fine-grained layered structure. This is because the formation of large deformation bands and micro-bands under cold rolling conditions leads to the formation of heterogeneous structures after annealing. The initial deformation structure and the non-uniform precipitation during annealing contribute to the formation of heterogeneous structures. Figure 10As shown, the T5 alloy prepared in Example 5 exhibits a significant reduction in grain size and the appearance of numerous white precipitates at the grain boundaries due to the addition of W. Based on thermodynamic calculations and experimental results, Ni and Co stabilize the FCC phase, but Cr and W, which possess a BCC structure, destabilize the FCC solid solution. Furthermore, the addition of W increases the metastable state of the T5 alloy. In the T5 alloy, W is abundant at the grain boundaries, forming a second phase.

[0068] Table 2

[0069] Table 3

[0070] To analyze the mechanical properties of alloys B1, T1, T2, T3, T4, and T5, hardness tests were first conducted. Table 4 shows the hardness values ​​and errors of alloys B1, T1, T2, T3, T4, and T5. Each sample was tested at least five times. As shown in Table 4, the addition of Al reduced the hardness of the annealed alloy to 197 HV, while the hardness of the CoCrNi alloy without added elements was 204 HV, showing little change. The hardness values ​​of the Ti-added, Nb-added, and Ta-added alloys were 447 HV, 441 HV, and 473 HV, respectively, showing a significant increase compared to the CoCrNi alloy without added elements. Calculations showed that the hardness of the Ti-added alloy increased by 119%, the Nb-added alloy by 116%, and the Ta-added alloy by 132%. This is mainly due to the formation of heterogeneous structures and a large number of nano-precipitates in the alloys.

[0071] Table 4

[0072] To further investigate the mechanical properties of alloys B1, T1, T2, T3, T4, and T5, room temperature tensile property tests were conducted, such as... Figure 11As shown, alloys B1 and T1 exhibit similar tensile properties, both possessing high tensile plasticity (nearly 80%). However, their yield strengths are relatively low, with B1 having a yield strength of 302.5 MPa and T1 327.2 MPa. The tensile strength of B1 is 797.6 MPa, while that of T1 is 821.2 MPa. For alloy T2, the addition of Ti significantly improves both yield strength and tensile strength, resulting in yield strength, tensile strength, and tensile plasticity values ​​of 1087.5 MPa, 1416.9 MPa, and 18.49%, respectively. For alloy T3, the addition of Nb significantly increases yield strength and tensile strength, reaching 1021.2 MPa and 1352.5 MPa, respectively. This substantial increase in strength is attributed to precipitation strengthening. Simultaneously, the significant decrease in plasticity is due to the brittle nature of the Laves phase; the introduction of a large amount of this brittle phase leads to a substantial reduction in the alloy's plasticity. The T4 alloy shows that increasing the Ta element significantly improves the yield strength and tensile strength, reaching 1147 MPa and 1410.2 MPa respectively, but reduces the plasticity to only 5%. The T5 alloy shows that adding W not only doubles the yield strength but also maintains nearly 55% of the plasticity. The yield strength, tensile strength, and tensile plasticity of the T5 alloy are 617.3 MPa, 1074.6 MPa, and 54.5%, respectively.

[0073] Tests showed that the CoCrNi alloy sample A1 prepared in Comparative Example 1 had a yield strength of 230.6 MPa, a tensile strength of 511.3 MPa, and a tensile plasticity of 75.12%. In contrast, the alloy sample prepared by liquid nitrogen cold rolling and annealing in Comparative Example 3 had yield strengths of 302.5 MPa, tensile strengths of 797.6 MPa, and tensile plasticity of 77.24%, respectively. This demonstrates that liquid nitrogen cold rolling and annealing treatments improve the mechanical properties of CoCrNi-based multi-principal element alloys to a certain extent.

[0074] To further verify the effect of liquid nitrogen cold rolling on the properties of the CoCrNi alloy system compared to ordinary cold rolling, two treatments, liquid nitrogen cold rolling and room temperature cold rolling, were performed to compare and analyze the differences between the two processes. By comparing the mechanical properties of samples A2 and B1 from Comparative Example 2 (ordinary cold rolling) and Comparative Example 3 (liquid nitrogen cold rolling), it can be seen that there are certain differences in tensile properties. The yield strength of alloy A2 was 291.6 MPa, and that of alloy B1 was 302.5 MPa; the tensile strength of alloy A2 was 785.4 MPa, and that of alloy B1 was 797.6 MPa; both alloys exhibited high tensile plasticity, with elongation close to 80%. It can be seen that compared to ordinary cold rolling, liquid nitrogen cold rolling can slightly improve both the yield strength and tensile strength of the alloy. This performance difference is mainly due to the fact that the extremely low temperature during liquid nitrogen cold rolling effectively suppresses dynamic recovery and dislocation annihilation behavior, resulting in a higher density of dislocations, stacking faults, and deformation twin structures within the alloy. These stored strains can serve as a nucleation driving force during subsequent recrystallization and aging processes, promoting grain refinement and dispersed distribution of precipitates, thereby achieving a better balance between strength and plasticity.

[0075] To verify the process advantage of this invention, which is "cumulative deformation of 80% across multiple passes and ≤1% per pass," a molding experiment was conducted comparing Comparative Example 5 and Example 3. Figure 12 As shown, in Comparative Example 5, after deformation using liquid nitrogen cold rolling processes with single-pass deformation amounts >10% and >20%, premature crack initiation and propagation occurred in the alloy during deformation, ultimately leading to sample fracture and failure to reach 80% cumulative deformation. This indicates that under low-temperature conditions, large single-pass deformation introduces excessive strain concentration and dislocation accumulation within the alloy, causing severe stress inhomogeneity and strain localization, thereby inducing stacking fault aggregation, microcrack formation, and enhanced intergranular fracture tendency. In contrast, the present invention employs a multi-pass progressive deformation process with single-pass deformation amounts ≤1%, which effectively disperses strain energy and avoids the risk of microcrack initiation caused by instantaneous strain concentration. Simultaneously, during the accumulation of 80% large plastic deformation, dislocation cross-slip, stacking faults, and deformation twins are gradually induced to continuously generate, achieving sufficient storage and uniform distribution of deformation energy, providing high-density nucleation sites for subsequent recrystallization annealing. After recrystallization annealing at 1173 K and aging treatment at 973 K, uniform and refined grains and dispersed precipitates are formed inside the sample, which together construct a stable multi-scale heterogeneous structure, thereby significantly improving the strength and ductility of the material. The liquid nitrogen cold rolling process parameter design adopted in this invention, which has a cumulative deformation of 80% over multiple passes and ≤1% per pass, balances high strain accumulation and microstructural stability, ensuring deformation integrity while avoiding early fracture caused by over-processing, and achieving comprehensive mechanical properties that are significantly superior to single-pass large deformation processes.

[0076] It should be noted that the present invention is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments that have the same structure and perform the same effects as the technical concept within the scope of the present invention are included within the scope of the present invention. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of the present invention, are also included within the scope of the present invention.

Claims

1. A CoCrNi-based multi-principal element alloy with controllable strength and ductility, characterized in that, According to the atomic percentage, the alloy comprises the following components: 32-36% of Co, 30-34% of Cr, 28-32% of Ni and 2-6% of X, wherein X comprises at least one of B, C, Al, Si, Sc, Ti, V, Mn, Fe, Cu, Zr, Nb, Mo, Hf, Ta, W and Re; the CoCrNi-based multi-principal element alloy has an FCC structure as a matrix and contains a nano-sized precipitated phase dispersedly distributed.

2. The CoCrNi-based multi-principal element alloy with controllable strength and ductility according to claim 1, characterized in that, The CoCrNi-based multi-principal element alloy has a composition of Co 34 Cr 32 Ni 30 Al4or Co 34 Cr 32 Ni 30 Ti4or Co 34 Cr 32 Ni 30 Nb4or Co 34 Cr 32 Ni 30 Ta or Co 34 Cr 32 Ni 30 W4.

3. The preparation method of the CoCrNi-based multi-principal element alloy with controllable strength and ductility according to any one of claims 1-2, characterized in that, The method comprises the following steps: S1, respectively taking Co, Cr, Ni and doped element X metal elementary raw materials, proportioning and then performing vacuum arc furnace smelting to obtain an alloy ingot; S2, performing vacuum suction casting on the alloy ingot to obtain a cast alloy plate; S3, performing homogenization annealing treatment on the cast alloy plate; S4, performing cold rolling deformation treatment on the alloy plate after the homogenization annealing treatment under liquid nitrogen cooling condition, with a total deformation of 50-85%; S5, performing recrystallization annealing and aging treatment on the sample after the cold rolling deformation to obtain the CoCrNi-based multi-principal element alloy.

4. The method of manufacturing a CoCrNi-based multi-principal element alloy with controllable strength and ductility according to claim 3, characterized in that, In the step S1, the purity of the metal elementary raw material is greater than or equal to 99.99%; and the metal elementary raw material is subjected to oxidation layer removal treatment before smelting.

5. The method of claim 3, wherein the CoCrNi-based multi-principal element alloy with controllable strength and ductility is prepared by the steps of: preparing a CoCrNi-based multi-principal element alloy by mixing Co, Cr, Ni, and other elements; and performing heat treatment on the CoCrNi-based multi-principal element alloy. In the step S1, the vacuum arc smelting is specifically as follows: the arc smelting furnace is vacuumized, high-purity argon gas is filled for protection, and the smelting is turned over 5-6 times under the protection of high-purity argon gas to obtain the alloy ingot.

6. The method of manufacturing a CoCrNi-based multi-principal element alloy with controllable strength and ductility according to claim 4, wherein, The current of the vacuum arc smelting is 200-400 A, and the time of the vacuum arc smelting is 60-80 s / time.

7. The method of manufacturing a CoCrNi-based multi-principal element alloy with controllable strength and ductility according to claim 3, characterized in that, In the step S3, the temperature of the homogenization annealing treatment is 1373-1573 K, and the time is 1-2 h.

8. The method of manufacturing a CoCrNi-based multi-principal element alloy with controllable strength and ductility according to claim 3, characterized in that, In the step S4, the single-pass deformation in the cold rolling deformation treatment is less than or equal to 1%, and the rolling speed is 10-20 m / min.

9. The method of manufacturing a CoCrNi-based multi-principal element alloy with controllable strength and ductility according to claim 3, wherein, In the step S5, the temperature of the recrystallization annealing treatment is 1073-1273 K, and the time is 0.5-1 h.

10. The method of manufacturing a CoCrNi-based multi-principal element alloy with controllable strength and ductility according to claim 3, wherein, In the step S5, the temperature of the aging treatment is 873-1073 K, and the time is 4-6 h.

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