Copper alloy and method for producing the same

Abstract

The application belongs to the field of metallurgy, and provides a copper alloy and a preparation method thereof.The copper alloy comprises a copper matrix and high-entropy alloy nano precipitated phases distributed in the copper matrix, and the high-entropy alloy nano precipitated phases comprise iron elements, cobalt elements, nickel elements and chromium elements.The application introduces high-entropy alloys as nano precipitated phases into the copper matrix, and the obtained copper alloy simultaneously has high electrical conductivity and thermal conductivity, and strength and ductility.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metallurgy, and particularly relates to a copper alloy and a preparation method thereof. BACKGROUND

[0002] Alloys used in electrical appliances, semiconductors and nanodevices often require high electrical conductivity, high thermal conductivity, high strength and high ductility. Traditional strengthening methods of alloys mainly include fine-grain strengthening, nanotwin strengthening and second-phase nanophase strengthening. However, the traditional strengthening strategies can introduce various defects into the alloy while improving the strength, resulting in the decline of the performance of the alloy in electrical conductivity, thermal conductivity and ductility.

[0003] Fine-grain strengthening is to refine the grains of the alloy to improve the strength of the alloy, but the introduced grain boundaries can sacrifice the ductility, electrical conductivity and thermal conductivity of the alloy; nanotwin strengthening is to introduce twin boundaries to improve the yield strength and electrical conductivity of the alloy, but the introduced twin boundaries can reduce the ductility of the alloy; second-phase nanophase strengthening is to introduce a high density of nanometer precipitates as obstacles for dislocation movement, but due to the large lattice mismatch between the nanometer precipitates and the matrix, the electrical conductivity and thermal conductivity of the alloy are both low. In addition, some alloys are also strengthened by introducing high electrical conductivity / thermal conductivity materials, such as graphene / copper composites, but the strength of the alloy prepared by this method increases by a small margin.

[0004] Therefore, the current copper alloy still needs to be improved. SUMMARY

[0005] The present application aims to at least partially solve one of the technical problems in the related art.

[0006] In one aspect of the present application, a copper alloy is provided, comprising a copper matrix and high-entropy alloy nanometer precipitates distributed therein, the high-entropy alloy nanometer precipitates comprising iron elements, cobalt elements, nickel elements and chromium elements. The copper alloy is formed by introducing high-entropy alloy nanometer precipitates to strengthen the copper matrix, and the copper alloy has high electrical conductivity and thermal conductivity, as well as high strength and ductility.

[0007] According to an embodiment of the present application, the chemical formula of the copper alloy is (Fe a Co b Ni c Cr d ) x Cu 100-x , wherein 5≤a≤35, 5≤b≤35, 5≤c≤35, 5≤d≤35, and a+b+c+d=100, 2≤x≤20.

[0008] According to an embodiment of the present application, in the chemical formula of the copper alloy, 20≤a≤30, 20≤b≤30, 25≤c≤35, 15≤d≤25, and a+b+c+d=100.

[0009] According to an embodiment of the present application, in the chemical formula of the copper alloy, 4≤x≤15.

[0010] According to an embodiment of the present application, the chemical formula of the copper alloy is (Fe 26 Co 26 Ni 29 Cr 19 ) x Cu 100-x . Thus, the comprehensive performance of the copper alloy is further improved.

[0011] According to an embodiment of the present application, the average diameter of the high-entropy alloy nano precipitates is 3.5nm-9nm. The distortion degree between the high-entropy alloy nano precipitates with smaller average diameter and the copper matrix interface is lower, so that the high-entropy alloy nano precipitates and the copper matrix maintain higher coherence.

[0012] According to an embodiment of the present application, the density of the high-entropy alloy nano precipitates in the copper matrix is not less than 5.6×10 22 / m 3 . Optionally, the density of the high-entropy alloy nano precipitates in the copper matrix is 5.6×10 22 / m 3 -2.4×10 23 / m 3 . These high-density high-entropy alloy nano precipitates are dispersed in the copper matrix, so that the copper alloy exhibits higher strength and ductility.

[0013] According to an embodiment of the present application, the high-entropy alloy nano precipitates have a face-centered cubic structure (FCC). The high-entropy alloy nano precipitates with a face-centered cubic structure are dispersed in the copper matrix, and can maintain coherent structure with the copper matrix which also has a FCC structure in different crystal orientations.

[0014] According to an embodiment of the present application, the copper matrix and the high-entropy alloy nano precipitates form a coherent structure. Thus, the ductility and strength of the copper alloy can be improved.

[0015] In another aspect of the present application, the present application provides a method for preparing the copper alloy, comprising the following steps:

[0016] (1) ingredients of metallic iron, metallic cobalt, metallic nickel, metallic chromium and metallic copper are prepared, and an alloy ingot is prepared by melting and suction casting;

[0017] (2) sequentially performing first annealing treatment, cold rolling and second annealing treatment on the alloy ingot to prepare a copper alloy.

[0018] The method of the present application can refine the diameter of the nano precipitated phase in the copper alloy and increase the density of the nano precipitated phase in the copper matrix, so that the copper alloy has high electrical conductivity and thermal conductivity, and also has high strength and ductility.

[0019] According to the embodiment of the present application, the melting and suction casting processes are both carried out under a protective gas. Thus, the alloy melt in the melting and suction casting processes can be prevented from being oxidized, so as to improve the purity of the alloy ingot.

[0020] According to the embodiment of the present application, the melting is multiple melting, the temperature of each melting is not less than 1750K, the time of each melting is 30s-60s, and the number of melting is at least 20 times. Thus, the metal iron, metal cobalt, metal nickel, metal chromium and metal copper can be more uniformly mixed after being melted.

[0021] According to the embodiment of the present application, the melting is vacuum induction arc melting, and the current of the melting is 200A-500A. In this way, the volatilization of alloy elements can be avoided while ensuring the uniformity of the composition of the alloy melt.

[0022] According to the embodiment of the present application, the first annealing treatment is vacuum annealing. The first annealing treatment under vacuum atmosphere can avoid the secondary oxidation of the alloy ingot and promote the formation of a copper alloy with higher purity.

[0023] According to the embodiment of the present application, the temperature of the first annealing treatment is 600K-800K, and / or the time of the first annealing treatment is 9h-12h. Thus, the diameter of the high-entropy alloy nano precipitated phase can be refined and the precipitation of the high-entropy alloy nano precipitated phase can be promoted through the first annealing treatment.

[0024] According to the embodiment of the present application, the second annealing treatment is vacuum annealing. The second annealing treatment under vacuum atmosphere can avoid the secondary oxidation of the alloy sheet after cold rolling and promote the formation of a copper alloy with higher purity.

[0025] According to the embodiment of the present application, the temperature of the second annealing treatment is 300K-500K, and / or the time of the second annealing treatment is 1.5h-3h. Thus, the dislocation generated in the process of cold rolling of the copper alloy can be reduced through the second annealing treatment, so as to reduce the internal stress of the copper alloy and improve the ductility and strength of the copper alloy.

[0026] According to the embodiment of the present application, the deformation amount of the cold rolling is 60%-80%. Thus, the grain can be further refined and the strength of the material can be improved by controlling the deformation amount of the cold rolling. BRIEF DESCRIPTION OF DRAWINGS

[0027] The above and / or additional aspects and advantages of the present application will become apparent and be readily understood from the following description, taken in conjunction with the accompanying drawings, in which:

[0028] Figure 1 is a stress-strain curve and a scanning electron microscope image of a tensile fracture of a copper alloy according to some embodiments of the present application and comparative examples;

[0029] Figure 2 is a resistivity-temperature curve according to some embodiments of the present application and comparative examples;

[0030] Figure 3 is a product of yield strength and uniform elongation-conductivity curve surface according to some embodiments of the present application and comparative examples;

[0031] Figure 4 is a scanning electron microscope image of a tensile fracture of a copper alloy according to some embodiments of the present application;

[0032] Figure 5 is a thermal conductivity curve of a copper alloy according to some embodiments of the present application and comparative examples;

[0033] Figure 6 is a microstructure and high-entropy alloy nano precipitate phase composition diagram of a copper alloy according to some embodiments of the present application;

[0034] Figure 7 is an electron backscatter diffraction diagram of a copper alloy according to some embodiments of the present application;

[0035] Figure 8 is a high-entropy alloy nano precipitate phase and corresponding energy spectrum diagram in a copper alloy according to some embodiments of the present application;

[0036] Figure 9 is a copper alloy atomic structure micrograph and corresponding energy spectrum diagram according to some embodiments of the present application;

[0037] Figure 10 is a transmission electron microscope image of a copper alloy according to some embodiments of the present application and comparative examples. DETAILED DESCRIPTION

[0038] Embodiments of the present application are described in detail below, with the purpose of explaining the present application, and should not be understood as limiting the present application.

[0039] The inventors found that the mixing enthalpy between Fe, Co, Ni and Cr elements is not greater than zero, and the mixing enthalpy between each of them and copper is positive. The elements with positive mixing enthalpy cannot form precipitates when introduced into a copper matrix, while the above-mentioned elements with mixing enthalpy not greater than zero can form high-entropy alloy nano precipitates in the copper alloy.

[0040] Accordingly, the first aspect of the present application provides a copper alloy, which comprises a copper matrix and high-entropy alloy nano precipitates distributed therein, the high-entropy alloy nano precipitates comprising iron element, cobalt element, nickel element and chromium element. The copper alloy has the copper matrix with the high-entropy alloy nano precipitates distributed therein, so that the copper alloy has both relatively optimal electrical conductivity and thermal conductivity and relatively high strength and ductility. Specifically, the dispersed high-entropy alloy nano precipitates match the copper matrix by self-adapting the lattice parameters, and such lattice self-adapting capability avoids introducing high-density mismatch dislocations into the copper matrix, reduces the scattering rate of electrons and phonons in the copper alloy, and thus improves the electrical conductivity and thermal conductivity of the copper alloy; in addition, the lattice spacing of the high-entropy alloy nano precipitates is basically consistent with that of the copper matrix around the high-entropy alloy nano precipitates, so that the copper alloy exhibits relatively optimal ductility and relatively high strength.

[0041] In some embodiments, the chemical formula of the copper alloy is (Fe a Co b Ni c Cr d ) x Cu 100-x , wherein (Fe a Co b Ni c Cr d ) x represents the composition of the high-entropy alloy nano precipitates, and Cu 100-x represents the copper matrix. It can be understood that the chemical formula is only used to explain the relative atomic content of each metal element in the copper alloy of the present application, so as to reflect that the copper matrix (Cu) has the high-entropy alloy nano precipitates comprising Fe element, Co element, Ni element and Cr element distributed therein. In addition, it should also be understood that the chemical formula does not represent a closed meaning, and it is well known in the art that due to the characteristics and preparation methods of the alloy and other factors, copper element may inevitably exist in the precipitates, but the content of the copper element is so low that it can be ignored in the chemical formula, and the content of the copper element in the precipitates in the present application is not higher than 1 at%.

[0042] In the copper alloy, the value of x is in the range of 2≤x≤20, for example, x is 2, 4, 4.5, 5, 6, 6.5, 7, 8, 9, 10, 10.5, 11, 12, 13, 14, 15, 20, etc. Preferably, the value of x satisfies 4≤x≤15.

[0043] In the copper alloy, a, b, c and d satisfy the following conditions: 5≤a≤35, 5≤b≤35, 5≤c≤35, 5≤d≤35, and a+b+c+d=100. Alternatively, 20≤a≤30, 20≤b≤30, 25≤c≤35, 15≤d≤25, and a+b+c+d=100.

[0044] In some embodiments, the chemical formula of the copper alloy is (Fe 26 Co 26 Ni 29 Cr 19 ) x Cu 100-x Therefore, this copper alloy has high overall performance.

[0045] According to the present invention, a high-entropy alloy nanoprecipitate is distributed in a copper matrix. In some embodiments, the average diameter of the high-entropy alloy nanoprecipitate is 3.5 nm to 9 nm, for example, 3.5 nm, 4.4 nm, 5 nm, 5.5 nm, 6 nm, 8 nm, 9 nm, etc. This smaller average diameter of the high-entropy alloy nanoprecipitate results in lower distortion at the interface with the copper matrix, thereby maintaining a high degree of coherence between the high-entropy alloy nanoprecipitate and the copper matrix.

[0046] In some embodiments, the density of the high-entropy alloy nanoprecipitates in the copper matrix is ​​not less than 5.6 × 10⁻⁶. 22 pcs / m 3 Optionally, the density of the high-entropy alloy nanoprecipitates in the copper matrix is ​​5.6 × 10⁻⁶. 22 pcs / m 3 -2.4×10 23 pcs / m 3 These high-density, high-entropy alloy nano-precipitates are dispersed in the copper matrix, giving the copper alloy high strength and ductility.

[0047] In some embodiments, the high-entropy alloy nanoprecipitates in the copper alloy possess a face-centered cubic (FCC) structure. These FCC-structured high-entropy alloy nanoprecipitates are dispersed within the copper matrix and maintain a coherent structure with the copper matrix, which also has an FCC structure, even under different crystal orientations. This indicates that the precipitates possess the long-range chemical disorder structure of a high-entropy bulk alloy. Furthermore, combined with the structural characterization by transmission electron microscopy and atomic probe microanalysis, this precipitate exhibits the long-range chemical disorder properties of a FCC structure. Such Fe, Co, Ni, and Cr enriched nanoprecipitates with a simple FCC structure can be considered high-entropy alloy nanoprecipitates.

[0048] In some embodiments, the average grain diameter of the copper alloy is 690nm-990nm. By controlling the average diameter of the copper alloy within the above range, the yield strength and tensile strength of the copper alloy can be improved.

[0049] In some embodiments, the copper matrix and the high-entropy alloy nanoprecipitates form a coherent structure. This coherent structure lacks a clear interface between the copper matrix and the high-entropy alloy nanoprecipitates, and the lattice spacing of the high-entropy alloy nanoprecipitates is essentially consistent with that of the surrounding copper matrix. Because this coherent structure reduces the scattering rate of electrons and phonons by the copper alloy, it results in higher electrical and thermal conductivity. Furthermore, the reactive forces generated by the entropy barrier of the high-entropy alloy nanoprecipitates, due to their short-range chemical order, hinder dislocation movement and cross-slip, further enhancing the ductility and strength of the copper alloy.

[0050] According to another aspect of the present invention, a method for preparing a copper alloy is provided, comprising the following steps:

[0051] (1) According to the atomic percentage of each element in the copper alloy, the metal iron, metal cobalt, metal nickel, metal chromium and metal copper are batched, and alloy ingots are prepared by smelting and casting.

[0052] (2) The alloy ingot is subjected to a first annealing treatment, cold rolling and a second annealing treatment in sequence to prepare a copper alloy.

[0053] In the method provided by this invention, Fe, Co, Ni, and Cr elements, whose enthalpy of mixing between any two elements is not greater than zero, are introduced into a copper matrix (refer to Table 1 for the enthalpy of mixing between elements) to form a high-entropy alloy nano-precipitate phase in the copper alloy. The process involves suction casting of the molten alloy to refine the diameter of the primary phase, allowing it to dissolve into the copper matrix as much as possible. A first annealing treatment promotes the precipitation of the high-entropy alloy precipitate phase, which is then dispersed throughout the copper matrix. Cold rolling aims to refine the grain structure of the copper alloy, thereby improving its strength. A second annealing treatment reduces dislocations generated during the cold rolling process, thus reducing the internal stress of the copper alloy and improving its toughness.

[0054] Table 1

[0055]

[0056] In some embodiments, the purity of metallic iron, metallic cobalt, metallic nickel, metallic chromium, and metallic copper is each independently not less than 99.99 wt%.

[0057] In some embodiments, the method further includes ultrasonic cleaning of the surface of at least one of the metals iron, cobalt, nickel, chromium, and copper using acetone, anhydrous ethanol, etc.

[0058] According to the present invention, metallic iron, metallic cobalt, metallic nickel, metallic chromium and metallic copper are melted through a smelting process, and metallic copper is doped with metallic elements of iron, cobalt, nickel and chromium, and mixed uniformly.

[0059] In some embodiments, the melting is carried out under a protective gas. This protective gas prevents secondary oxidation of the alloy melt during the melting process. The protective gas may be selected from argon or nitrogen.

[0060] In some embodiments, the melting process is a series of melting operations.

[0061] The temperature for each melting process shall not be less than 1750K, such as 1750K, 1800K, 1850K, 1900K, etc. Optionally, the temperature for each melting process shall be 1750K-1850K.

[0062] Each melting session lasts 30-60 seconds, for example, 30 seconds, 40 seconds, 50 seconds, 60 seconds, etc.

[0063] In some implementations, the number of melting cycles is at least 20, such as 20, 21, 22, 23, 24, 25, 30, etc. Optionally, the number of melting cycles is 20-25.

[0064] In some embodiments, the melting process employs a vacuum induction arc melting process, the process conditions of which include controlling the current of the vacuum induction arc furnace to 200A-500A, such as 200A, 300A, 400A, 500A, etc. This ensures the uniformity of the alloy melt composition while preventing the volatilization of alloying elements.

[0065] According to the present invention, a suction casting process is used to cast the alloy melt obtained by melting. During the suction casting process, the alloy melt enters the mold cavity from bottom to top, so that the alloy melt is in close contact with the cavity wall to accelerate the solidification of the alloy melt. Moreover, this close contact between the alloy melt and the cavity wall allows the alloy melt to solidify directionally from the cavity wall towards the center of the wall thickness, which can reduce the shrinkage porosity of the alloy ingot.

[0066] In some embodiments, the suction casting is performed under vacuum conditions. Performing the suction casting process under a vacuum atmosphere can avoid air entrapment and prevent secondary oxidation of the alloy melt.

[0067] The casting mold cavity is cylindrical, and the cylindrical cavity has a large outer surface area, which is beneficial to increase the contact area between the alloy melt in the cavity and the cooling water, improve the solidification rate of the alloy melt in the cavity, precipitate a large number of high-density primary phases, and refine the diameter of the primary phases.

[0068] The suction casting process may include: continuously circulating cooling water into the inner wall of the mold cavity to accelerate the solidification and cooling of the alloy melt within the cavity, thereby refining the size of the high-entropy alloy nano-precipitates and reducing their segregation. Optionally, the temperature of the cooling water introduced into the mold cavity is 285K-293K. Furthermore, during the suction casting process, the process ends when the temperature of the mold cavity cools to 285K-293K.

[0069] In some embodiments, the first annealing process is vacuum annealing. A first annealing process under a vacuum atmosphere can prevent secondary oxidation of the alloy ingot and promote the formation of a copper alloy with higher purity.

[0070] In some embodiments, the temperature of the first annealing treatment is 600K-800K, such as 600K, 650K, 700K, 750K, 800K, etc.; and / or the time of the first annealing treatment is 9h-12h, such as 9h, 10h, 11h, 12h, etc. The first annealing treatment can refine the high-entropy alloy nano-precipitates and promote their precipitation.

[0071] In some embodiments, the second annealing process is vacuum annealing. The second annealing process under a vacuum atmosphere can prevent secondary oxidation of the cold-rolled alloy sheet and promote the formation of a copper alloy with higher purity.

[0072] In some embodiments, the temperature of the second annealing treatment is 300K-500K, such as 300K, 350K, 400K, 450K, 500K, etc.; and / or the time of the second annealing treatment is 1.5h-3h, such as 1.5h, 2h, 2.5h, 3h, etc. The second annealing treatment can reduce the dislocations generated during the cold rolling process of the copper alloy, thereby reducing the internal stress of the copper alloy and improving its ductility and strength.

[0073] According to the present invention, the alloy ingot after the first annealing treatment is subjected to cold rolling, which further refines the grain structure of the copper alloy to improve its strength. Optionally, the deformation amount of the cold rolling is 60%-80%.

[0074] In the method of this invention, through melting, suction casting, a first annealing treatment, cold rolling, and a second annealing treatment, a large number of dispersed high-entropy alloy nano-precipitates are formed in the copper alloy, thereby strengthening the copper matrix. The resulting copper alloy exhibits high electrical and thermal conductivity, as well as high strength and ductility. Furthermore, the copper content in the high-entropy alloy nano-precipitates obtained by the method of this invention is less than 1 at%, and the content of solid solution atoms in the high-entropy alloy nano-precipitates can be further reduced by adjusting the element content and subsequent heat treatment during the preparation process.

[0075] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0076] Example 1

[0077] (1) Ingredients

[0078] Five pure metal blocks of Fe, Co, Ni, Cr and Cu with purities of 99.99 wt% were selected according to their chemical formulas (Fe... 26 Co 26 Ni 29 Cr 19 )6Cu 94 The ingredients are calculated based on the atomic ratio shown, and the total mass of the ingredients is 40g.

[0079] (2) Smelting

[0080] Five prepared metals were placed into a vacuum induction arc furnace, and the furnace was evacuated to a vacuum level of 10. -3 Pa, then argon gas is introduced into the furnace cavity, and the circulating cooling water system is turned on to introduce cooling water at a temperature of 288K. Magnetic stirring is introduced into the melting process, and the current is controlled at 300A. Each melting lasts 45 seconds, and the melting is repeated 20 times to obtain the alloy melt.

[0081] (3) Suction casting

[0082] During the suction casting process, cooling water at a temperature of 288K is introduced into the inner wall of the mold cavity, causing the alloy melt to solidify and cool in the cylindrical mold cavity. The suction casting ends when the temperature of the mold cavity cools down to 288K, resulting in a cylindrical alloy ingot with a height of 10mm and a diameter of 10mm.

[0083] (4) First annealing treatment

[0084] The temperature of the first annealing treatment was controlled at 700K, and the alloy ingot was annealed in a vacuum atmosphere for 10 hours.

[0085] (5) Cold rolling

[0086] The alloy ingot after the first annealing treatment is cold rolled into a 3mm thick sheet, that is, the deformation of the cold rolling is controlled to be 70%.

[0087] (6) Second annealing treatment

[0088] The cold-rolled sheet was vacuum annealed at 500K for 2 hours to obtain a copper alloy sheet (6HEA-Cu).

[0089] Example 2

[0090] Copper alloy sheets (15HEA-Cu) were prepared according to the method of Example 1, except that the ingredients were adjusted. Five pure metal blocks of Fe, Co, Ni, Cr, and Cu with purities of 99.99 wt% were prepared according to the chemical formula (Fe... 26 Co 26 Ni 29 Cr 19 ) 15 Cu 85 The ingredients are prepared according to the atomic ratio shown, and the total mass of the ingredients is 40g.

[0091] Example 3

[0092] Copper alloy sheets (4HEA-Cu) were prepared according to the method of Example 1, except that the ingredients were adjusted. Five pure metal blocks of Fe, Co, Ni, Cr, and Cu with purities of 99.99 wt% were prepared according to the chemical formula (Fe...). 26 Co 26 Ni 29 Cr 19 )4Cu 96 The ingredients are prepared according to the atomic ratio shown, and the total mass of the ingredients is 40g.

[0093] Example 4

[0094] Copper alloy sheets (2HEA-Cu) were prepared according to the method of Example 1, except that the ingredients were adjusted. Five pure metal blocks of Fe, Co, Ni, Cr, and Cu with purities of 99.99 wt% were prepared according to the chemical formula (Fe... 26 Co 26 Ni 29 Cr 19 )2Cu 98 The ingredients are prepared according to the atomic ratio shown, and the total mass of the ingredients is 40g.

[0095] Example 5

[0096] Copper alloy sheets (20HEA-Cu) were prepared according to the method in Example 1, except that the ingredients were adjusted. Five pure metal blocks of Fe, Co, Ni, Cr, and Cu with purities of 99.99 wt% were prepared according to the chemical formula (Fe... 26 Co 26 Ni 29 Cr 19 ) 20 Cu 80 The ingredients are prepared according to the atomic ratio shown, and the total mass of the ingredients is 40g.

[0097] Comparative Example 1

[0098] The smelting, suction casting, first annealing, cold rolling, and second annealing processes are the same as in Example 1, except that the ingredients contain only Cu with a purity of 99.99 wt% and a mass of 40 g.

[0099] Test case

[0100] The copper alloys obtained in Examples 1-5 and Comparative Example 1 were subjected to the following performance tests.

[0101] 1. Yield strength, tensile strength, and elongation

[0102] Copper alloy specimens were cut into dog-bone shapes (5mm × 3mm × 2mm) using electrical discharge machining (EDM), and then carefully polished with silicon carbide abrasive paper. Before tensile testing, the dog-bone specimens were annealed at 473K for 1 hour to eliminate residual machining stress. Tensile tests were then performed on an Instron Micro Tester 5948 at room temperature with a wire feed rate of 1 × 10⁻⁶. - 3 The tensile force is applied along the rolling direction. At least three specimens of the copper alloy for each embodiment and comparative example are tested, and the average value is taken.

[0103] 2. Electrical conductivity

[0104] The electrical conductivity of the copper alloy was measured using the standard four-probe method. The sample had a cross-sectional area of ​​10 mm × 10 mm and a thickness of 0.2 mm. The electrical conductivity was calculated using σ = 1 / ρ = L / RS, where ρ is resistivity, R is resistance, L is the distance between the two electrodes, and S is the cross-sectional area. This application tested the electrical conductivity of the copper alloy in the range of 2 K–300 K. Table 2 shows the electrical conductivity values ​​of the copper alloy at 300 K.

[0105] 4. Diameter and density of nano-precipitates in high-entropy alloys

[0106] The average diameter and density of nanoprecipitated phases in high-entropy alloys were measured using a three-dimensional atomic probe (APT) and transmission electron microscopy.

[0107] The test results are shown in Table 2.

[0108] Table 2

[0109]

[0110] As can be seen from the table above, compared with the pure copper of Comparative Example 1, the copper alloys prepared in Examples 1-5 have higher comprehensive mechanical properties, that is, they have both higher strength and toughness. Furthermore, Examples 1-5 show that when x is 4-15, the copper alloys exhibit better comprehensive properties, namely better yield strength, tensile strength, total elongation, uniform elongation, and room temperature conductivity. In the copper alloys with better comprehensive properties, the density of the high-entropy alloy nano-precipitates is higher than that of the alloys with x < 4 and x > 15, and the diameter of the high-entropy alloy nano-precipitates is smaller than that of the copper alloys with x > 15.

[0111] Figure 1 The figure shows the engineering stress-strain curves of 6HEA-Cu, oxide nanoparticle-reinforced copper (ODS-Cu), nanocrystalline copper (NC-Cu), and copper (Cu) of Comparative Example 1. In the figure, the ordinate of the inflection point of the stress-strain curve for 6HEA-Cu corresponds to the yield strength of 482 MPa, the ordinate of the highest point corresponds to the tensile strength of 632 MPa, the abscissa of the highest point corresponds to the uniform elongation of 25%, and the abscissa of the fracture surface corresponds to the total elongation of 33%. The figure shows that the plasticity of ODS-Cu and NC-Cu decreases rapidly, while 6HEA-Cu does not show a significant decrease in plasticity. The figure also shows the scanning electron microscope image of the fracture surface of 6HEA-Cu. The engineering stress-strain curve of ODS-Cu is based on the reference DOI: 10.1016 / j.msea.2018.06.010 (hereinafter referred to as "Reference 1"). Figure 8 The stress-strain curves for sample SPS0 in section a were plotted; the engineering stress-strain curves for NC-Cu were based on reference DOI: 10.1126 / science.1092905 (hereinafter referred to as "Reference 2"). Figure 2 (A) shows the stress-strain curve of sample NC-Cu.

[0112] Figure 2 These are resistivity-temperature curves for 6HEA-Cu, NC-Cu, ODS-Cu, and Cu. Figure 2 As can be seen, the resistivity of 6HEA-Cu, NC-Cu, ODS-Cu, and Cu all decreases linearly with temperature down to around 70K, and then decreases non-linearly below 70K. The resistivity of 6HEA-Cu is close to that of Cu throughout the measurement temperature range, exhibiting a relatively low level. The resistivity of NC-Cu is higher due to the high electron scattering rate of its high-density grain boundaries. ODS-Cu, due to the presence of a semi-coherent precipitate-matrix interface, also exhibits superior resistivity in the temperature range of 2K-300K. Therefore, the 6HEA-Cu alloy demonstrates good electrical conductivity. The resistivity-temperature curve of NC-Cu is based on reference 2. Figure 2(B) The resistivity-temperature curve of sample NC-Cu is plotted. The resistivity-temperature curve of ODS-Cu is obtained by making a sample according to the experimental procedure in Reference 1 and then using the conductivity test method described above in this invention.

[0113] Figure 3 This paper presents surface plots of the product of yield strength and uniform elongation versus electrical conductivity for 6HEA-Cu, 15HEA-Cu, and a series of grain-refined Cu alloys, nanoparticle-strengthened Cu alloys, nano-twin Cu alloys, and Cu-based composites. The "This work" section shows the test results for the product of yield strength and uniform elongation versus electrical conductivity for 6HEA-Cu and 15HEA-Cu. As can be seen from the figures, compared with grain-refined Cu alloys, NPs-strengthened Cu alloys, nano-twin Cu alloys, and Cu-based composites, 6HEA-Cu and 15HEA-Cu exhibit higher yield strength versus uniform elongation products and higher electrical conductivity. Figure 3In this study, the data and basis for the yield strength-uniform elongation product-conductivity surface plots of a series of grain-refined copper alloys were obtained from the following four references: DOI: 10.1016 / j.matdes.2011.07.029, DOI: 10.1038 / s43246-021-00150-1, DOI: 10.4028 / www.scientific.net / AMR.391-392.385 and DOI: 10.2320 / matertrans.45.2187. The data sources and basis for plotting the product of yield strength and uniform elongation versus electrical conductivity of a series of nanoparticle-reinforced copper alloys are from the following five references: DOI: org / 10.1063 / 1.4874655, DOI: 10.1016 / j.msea.2006.01.068, DOI: 10.1016 / j.msea.2012.12.007, DOI: 10.1016 / j.wear.2014.01.007 and DOI: 10.1016 / j.msea.2018.06.010. The data sources and basis for the yield strength vs. uniform elongation product-conductivity surface plots of a series of nanotwinned copper alloys are from the following three references: DOI: 10.1126 / science.1092905, DOI: 10.1016 / j.scriptamat.2014.11.032, and DOI: 10.1063 / 1.2816126. The data sources and basis for the yield strength vs. uniform elongation product-conductivity surface plots of a series of copper-based composite materials are from the following three references: DOI: 10.1016 / j.carbon.2017.02.089, DOI: 10.1038 / srep19363, and DOI: 10.1021 / acsnano.5b01067.

[0114] Figure 4 These are scanning electron microscope (SEM) images of the fracture surface of 6HEA-Cu at different magnifications.

[0115] Figure 5 The thermal conductivity of 6HEA-Cu and Cu in the higher temperature range is measured by preparing a sample with a thickness of 2 mm and a cross-sectional area of ​​10 mm × 10 mm and using a Linseis LFA467 laser flash diffuser. It can be seen that the thermal conductivity of 6HEA-Cu in the higher temperature range is close to 300 W / mk.

[0116] Figure 6 The diagram shows the microstructure of 6HEA-Cu and the composition of the nano-precipitated phases in the high-entropy alloy. Figure 6Image a shows a typical high-angle annular dark-field (HAADF) image of 6HEA-Cu under transmission electron microscopy, in which high-entropy alloy nanoprecipitates with high number density and uniform distribution can be observed in the copper matrix.

[0117] Figure 6 b is Figure 6 The high-magnification HAADF image of the high-entropy alloy nano-precipitate at region b in image a and its corresponding X-ray energy dispersive X-ray spectroscopy (EDX) are shown. The center of the copper energy dispersive X-ray spectrum is a circle without red, indicating that the high-entropy alloy nano-precipitate is rich in Fe, Co, Ni and Cr elements.

[0118] Figure 6 c is a three-dimensional reconstruction image of the high-entropy alloy nanoprecipitates obtained by atomic probe microanalysis (APT). The high-entropy alloy nanoprecipitates enriched with Ni, Co, Fe, and Cr elements can be observed. The calculated density of the high-entropy alloy nanoprecipitates is 2.4 × 10⁻⁶. 23 pcs / m 3 The diameters of multiple high-entropy alloy nano-precipitates were measured using Gatan Digital Micrograph software, and the average diameter of the high-entropy alloy nano-precipitates was found to be 4.5 nm.

[0119] Figure 6 d represents the quantitative analysis of elements in 6HEA-Cu. This figure shows that the nano-precipitates in the high-entropy alloy can be considered to have an almost equiatomic Fe content. 26 Co 26 Ni 29 Cr 19 Furthermore, the Cu content in the high-entropy alloy nano-precipitates is low, less than 1 at.%. The contents of Fe, Co, Ni, and Cr in the copper matrix are 0.8 at%, 0.44 at%, 3.54 at%, and 0.12 at%, respectively, while the Cu content is 95.04 at. The influence of these impurity atoms, which have very low solid solution content in the copper matrix, on the conductivity is negligible, especially in the low-temperature range.

[0120] Figure 7 The image shows the electron backscatter diffraction pattern of 6HEA-Cu, where RD represents the direction of movement during the rolling process, TD represents the vertical direction, and ND represents the normal direction of the rolling contact surface. This image illustrates the grain distribution of the copper alloy, with different colors representing grains of different crystal orientations. Statistical analysis of the electron backscatter diffraction patterns of 6HEA-Cu reveals that the average grain diameter of 6HEA-Cu is 880 nm.

[0121] Figure 8 The image shows the nano-precipitates of high-entropy alloys in 6HEA-Cu and their corresponding energy dispersive spectroscopy (EDS). Figure 8a represents the microstructure of the high-entropy alloy nanoprecipitates under transmission electron microscopy-bright-field microscopy (BF-TEM). Figure 8 b shows the high-angle annular dark-field (HAADF-STEM) image of the high-entropy alloy nano-precipitates and the energy spectrum of its elements. The image shows that fine, high-density high-entropy alloy nano-precipitates are dispersed in the copper matrix. The energy spectrum shows that the high-entropy alloy nano-precipitates contain Fe, Co, Cr and Ni elements.

[0122] Figure 9 To characterize the atomic structure microstructure and corresponding energy spectrum of 6HEA-Cu using the high-angle annular dark-field mode of transmission electron microscopy and an atom probe microanalysis, Figure 9 a is a microscopic diagram of the atomic structure of the crystal phase axis

[111] . Figure 9 b is the atomic structure microscopic diagram of the crystal phase axis

[001] . Figure 9 c is the atomic structure microscopic diagram of the crystal phase axis

[110] . Due to the low average atomic number of Fe, Co, Ni and Cr, in Figure 9 The darker color in a, 9b, and 9c represents the precipitated phase. The absence of a clear interface between this precipitated phase and the matrix indicates complete coherence between them. Furthermore, the Fast Fourier Transform (FFT) plots along the three axes show a face-centered cubic structure for both the precipitated phase and the matrix. No second set of diffraction points was observed in the FFT plots along these three axes, suggesting that the precipitated phase exhibits a long-range chemically disordered structure characteristic of high-entropy bulk alloys. (Elemental energy dispersive spectroscopy) Figure 9 Figure d shows that the precipitated phase contains Fe, Co, Ni, and Cr elements. Each atomic column of the precipitated phase appears to be randomly occupied by Fe, Co, Ni, and Cr, further confirming the long-range chemical disorder of the nanoprecipitated phase. Combining the structural characterization by transmission electron microscopy and atomic probe microanalysis, this precipitated phase exhibits a face-centered cubic structure with long-range chemical disorder. This nanoprecipitated phase enriched with Fe, Co, Ni, and Cr elements and possessing a simple face-centered cubic structure can be considered a high-entropy alloy nanoprecipitated phase. Figure 9 The red line in c represents the coherent interface. It can be seen that the nano-precipitates of the high-entropy alloy are completely coherent with the matrix, and the interface is a coherent interface.

[0123] Figure 10 These are high-magnification transmission electron microscopy images of copper alloys with x values ​​of 4, 6, 15, and 2, respectively, showing the diameters of the nano-precipitates in different high-entropy alloys.

[0124] Unless otherwise stated, all technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. All patents and publications related to this invention are incorporated herein by reference in their entirety. The terms "comprising" or "including" are open-ended expressions, meaning they include the contents specified in this invention but do not exclude other aspects.

[0125] Although embodiments of the present invention have been shown and described above in this specification, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method of producing a copper alloy, characterized by, The method comprises the following steps: (1) ingredients of metal iron, metal cobalt, metal nickel, metal chromium and metal copper are prepared into alloy ingot through smelting and suction casting; (2) the alloy ingot is sequentially subjected to first annealing treatment, cold rolling and second annealing treatment to prepare the copper alloy, the first annealing treatment is vacuum annealing, the temperature of the first annealing treatment is 600K-800K, and the time is 9h-12h; and / or, the second annealing treatment is vacuum annealing, the temperature of the second annealing treatment is 300K-500K, and the time is 1.5h-3h, the copper alloy comprises a copper matrix and high-entropy alloy nano precipitated phase distributed therein, the high-entropy alloy nano precipitated phase contains iron element, cobalt element, nickel element and chromium element, The chemical formula of the copper alloy is (Fe a Co b Ni c Cr d ) x Cu 100-x wherein 5≤a≤35, 5≤b≤35, 5≤c≤35, 5≤d≤35, and a+b+c+d=100, 2≤x≤20. The average diameter of the high-entropy alloy nano-precipitate phase is 3.5-9 nm, and the density in the copper matrix is not less than 5.6×10 22 / m 3 ; the high-entropy alloy nano precipitated phase has face-centered cubic structure; the copper matrix and the high-entropy alloy nano precipitated phase form a coherent structure.

2. The method of claim 1, wherein, 20≤a≤30, 20≤b≤30, 25≤c≤35, 15≤d≤25, and a+b+c+d=100.

3. The method of claim 1, wherein, 4≤x≤15。 4. The method of claim 1, wherein, The chemical formula of the copper alloy is (Fe 26 Co 26 Ni 29 Cr 19 ) x Cu 100-x .

5. The method of claim 1, wherein, The smelting and suction casting processes are both carried out under protective gas.

6. The method of claim 5, wherein, The smelting is multiple smelting, the temperature of each smelting is not less than 1750K, the time of each smelting is 30s-60s, and the number of smelting is at least 20 times.

7. The method of claim 5, wherein, The smelting adopts vacuum induction electric arc smelting process, and the process conditions include: the current is 200A-500A.

8. The method of claim 1, wherein, The deformation of the cold rolling is 60%-80%.

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