Copper-silver / three-dimensional network graphene composite electric contact material and preparation method thereof

Abstract

The invention discloses a copper-silver / three-dimensional network graphene composite electric contact material and a preparation method thereof.The preparation method comprises the steps that firstly, copper oxide raw material powder is reduced through hydrogen, and due to the volume shrinkage effect in the reduction process, a uniform and fine porous structure can be formed in the powder; then, a low-energy ball milling technology is adopted, the porous copper powder and the silver powder are mixed, and mixed powder with the alloyed surface is prepared; next, acetylene is used as a gas carbon source, low-temperature chemical vapor deposition is carried out in the mixed powder through an in-situ chemical vapor deposition method, hydrogenated graphite is introduced, gas can fully circulate in pores with the help of the existence of a porous structure, the hydrogenated graphite is evenly deposited on the surface of a porous wall, and the porous wall is formed; therefore, the hydrogenated graphite accurately copies the morphology of the porous skeleton; and finally, the copper-silver / three-dimensional network graphene composite electric contact material is successfully prepared through high-temperature rapid hot pressed sintering, solid solution quenching treatment, room-temperature rolling and annealing treatment.

Description

Technical Field

[0001] The invention belongs to the technical field of copper-based composite electrical performance materials, and in particular relates to a copper-silver / three-dimensional network graphene composite electrical contact material and a preparation method thereof. Background Art

[0002] With the advancement of new energy technologies, electric vehicles, communication systems, and other electronic devices, there is an increasing demand for electrical contacts with superior performance, stability, and reliability, as they play a key role in enabling and interrupting electrical current. Copper-silver alloys have been established as one of the most widely used and reliable materials for low-voltage electrical contacts due to their low electrical contact resistance, excellent thermal conductivity, and superior wear resistance. Given the high cost of silver-based materials, current research is increasingly focused on effectively reducing the silver content while innovating composite materials with excellent electrical contact properties. Graphene has excellent mechanical and electrical properties (such as a Young's modulus of approximately 1.1 TPa, a tensile strength of more than 130 GPa, and a carrier mobility of up to 2×10 5 cm 2 / (V·s)) as well as high melting point and chemical inertness against arc ablation can not only effectively improve the mechanical properties but also have the potential to achieve high electrical contact performance in Cu-Ag matrix composites. However, due to the agglomeration driven by van der Waals forces and the high 3 ) and graphene (2.2 g / cm 3), achieving uniform dispersion of graphene in a copper matrix remains challenging due to the significant density difference between graphene and metal matrices. In addition, the poor wettability between graphene and metal matrices further complicates the process of obtaining uniform dispersion. Currently, researchers have achieved in situ growth of high-quality graphene and successfully constructed a graphene network structure or analogous bicontinuous structure in a copper matrix. The network structure of graphene has recently become a research hotspot due to its isotropic properties. Patent No. CN109897985A discloses a three-dimensional continuous graphene / copper composite material and a preparation method thereof, Patent No. CN118531345A discloses a bicontinuous structure three-dimensional network graphene / copper composite material based on CuO reduction, Patent No. CN118531346A discloses a heterogeneous grain structure copper / three-dimensional network graphene composite material based on CuO reduction and a preparation method thereof, the document Composites Communications 53 (2025) 102191 reported a preparation method for a new three-dimensional graphene network reinforced copper-based composite material. The main technical effect of the technical solution disclosed in the above document is to achieve a composite material with good electrical conductivity and certain mechanical properties (tensile strength of about 300MPa). However, since the electrical contact material has high requirements for mechanical properties during use, the above research is lacking in achieving higher mechanical properties. The research is more inclined to basic preparation and mechanism research, lacks targeted application research, and is insufficient in evaluating the comprehensive electrical contact performance of network structure graphene in copper-silver based materials and conducting mechanism analysis. This highlights the necessity of further in-depth research. It is urgent to design a new copper-silver / graphene composite material, with the help of the solid solution strengthening of the Ag element and the effect of network graphene, to achieve the goal of low cost and high electrical contact performance under the condition of low silver content.

[0003] Current-carrying friction pairs are key components for transmitting signals and electricity. Copper-impregnated carbon is a sliding current-carrying friction pair composed of graphite blocks and copper materials, which is widely used due to its excellent conductivity and self-lubricating properties. These properties make it an important material for high-power DC motors, aircraft steering systems, wind turbines, and pantograph / catenary systems. Studies have shown that the performance and wear mechanism of copper / carbon pairs are affected by the coupling of mechanical and electrical factors and are related to the humidity of the environment. It is reported that water molecules can form strong hydrogen bonds in the carbon middle layer, destroying the ordered structure and converting it into an amorphous structure, thereby producing a lubricating effect. Other studies have shown that under high relative humidity conditions, H and OH molecules can passivate graphene, thereby reducing friction. H 2O molecules can penetrate graphene interlayers, passivating defects and edge dangling bonds. This process weakens the interaction between graphene layers, thereby reducing the friction coefficient. However, although humidity is a key factor affecting the wear behavior of copper / carbon friction pairs under actual subway operating conditions, managing humidity in large tunnels is technically challenging and costly. In addition, current research is insufficient in providing material-based solutions to address the root causes of abnormal wear phenomena.

[0004] In order to solve the above problems existing in the prior art, we propose a copper-silver / three-dimensional network graphene composite electrical contact material and a preparation method thereof. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing a copper-silver / three-dimensional network graphene composite electrical contact material.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for preparing a copper-silver / three-dimensional network graphene composite electrical contact material, comprising the following steps: S1. Reduction of the original CuO powder: The CuO powder is fed into a constant temperature zone in a rotary chemical vapor deposition rotary tube furnace, hydrogen is introduced, a temperature rise program is set, and the CuO powder is reduced to obtain a porous copper powder; S2. Mechanically mix the Cu and Ag powders by low-energy ball milling: place the reduced porous copper powder and silver powder in a ball milling jar for low-energy ball milling, wherein the silver powder accounts for 0.08-0.12% of the total mass, to obtain a Cu and Ag mixed powder; S3, deposition of hydrogenated graphite: feeding the Cu and Ag mixed powders into a constant temperature zone in a rotary chemical vapor deposition tube furnace, introducing argon, hydrogen and acetylene gases, setting a temperature rise program, and depositing hydrogenated graphite on the surface of the mixed powder under low temperature conditions to obtain a copper-silver / hydrogenated graphite composite powder; S4, rapid hot pressing sintering and growth of three-dimensional network graphene: placing copper-silver / hydrogenated graphite composite powder into a mold, sending the assembled mold into the working area of ​​a vacuum rapid hot pressing sintering furnace, closing the hatch, adjusting the heating program, performing rapid hot pressing sintering, waiting for natural cooling, taking out the graphite mold for demolding, and obtaining a copper-silver / three-dimensional network graphene composite material with three-dimensional network graphene grown inside; S5. Solution quenching treatment, room temperature rolling and annealing treatment: In order to promote the full solution of silver elements in the copper matrix and further improve the densification level of the material, the copper-silver / three-dimensional network graphene composite material is successively subjected to solution quenching treatment, room temperature rolling and annealing treatment to obtain a copper-silver / three-dimensional network graphene composite electrical contact material.

[0007] Preferably, the particle size of the CuO original powder in S1 is 0.1 μm-15 μm.

[0008] Preferably, in S1, the heating rate is 5-10°C / min, the reduction temperature is 200-400°C, the holding time is 2-5h, and the rotation rate is 170-200 rpm.

[0009] Preferably, the ball mill speed in S2 is 180-220 rpm, and the mixing time is 1-2 h; the ball-to-material ratio of low-energy ball milling is 8-10:1, and steel balls with a diameter of 5-8 mm are used.

[0010] Preferably, in S3, the heating rate is 5-10°C / min, the rotation rate is 170-200 rpm, the temperature for depositing hydrogenated graphite at low temperature is 200°C-400°C, and the hydrogenated graphite deposition time is 5-15min.

[0011] Preferably, the gas flow ratio of argon, hydrogen and acetylene during the S3 hydrogenated graphite deposition is 300-500:100-200:5-50.

[0012] Preferably, the rapid hot pressing sintering in S4 adopts a pressure of 30-50 MPa, a temperature of 750-900° C., a heating and pressure increasing time of 5-10 min, and a heat and pressure keeping time of 5-10 min.

[0013] Preferably, the solution quenching treatment method in S5 is: subjecting the copper-silver / three-dimensional network graphene composite material to solution treatment at 700-800°C for 1-3 hours, and then cooling the composite material to room temperature by rapid quenching to uniformly dissolve the silver in the copper matrix to form a stable solid solution structure.

[0014] Preferably, the composite material obtained in S5 is further subjected to annealing treatment, and the annealing temperature is set to 200-350° C. and the holding time is 1-3 hours to ensure that the internal stress of the material is completely released while maintaining the uniformity and stability of the microstructure.

[0015] Another object of the present invention is to provide a three-dimensional network copper-silver / three-dimensional network graphene composite electrical contact material prepared according to the above method.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] (1) The present invention prepares copper-silver-graphene composite powder by in-situ synthesis plus low-energy ball milling. This method helps to form a three-dimensional graphene network in situ while ensuring effective powder mixing. The subsequent high-temperature rapid hot pressing, solution quenching, room temperature rolling and annealing processes help to dissolve silver in the composite material and form a three-dimensional graphene network. These advantages synergistically improve the mechanical properties of the material, with a yield strength of up to 374MPa, a tensile strength of up to 425MPa, an elongation of up to 9.7%, a Vickers microhardness of up to HV178, and good thermal stability. The comprehensive performance is a major breakthrough compared to commercial copper-silver alloys.

[0018] (2) The present invention adds a very small amount of silver to the copper matrix, which greatly improves the performance of the composite material. First, in the field of copper-silver electrical contact materials, the higher the silver content, the better the electrical contact performance and the longer the contact life. However, silver is a precious metal, and a higher content means a higher cost. The present invention, on the premise of adding network graphene, can achieve a higher contact life with a very small amount of silver content, significantly reducing the cost. Secondly, compared with ordinary pure copper-graphene composite materials, in the copper-silver matrix, the role of silver is reflected in solid solution strengthening. Silver can be dissolved in the copper matrix, which improves the strength and hardness of the composite material. In addition, there is an interaction between silver and graphene. The silver element has a high wettability and can form a good interface with the graphene surface to improve the stability of the material. The presence of silver can reduce interface defects. Combined with the excellent slip of graphene, the wear resistance and flexibility of the composite material are improved.

[0019] (3) Key points in the preparation process: low-energy ball milling and solution quenching treatment. The porous copper powder and silver powder are mixed by low-energy ball milling. Due to the mechanical action during mixing, part of the surface of the copper powder and the silver powder will be pre-alloyed. There will be a preliminary surface bonding between different types of powders. While ensuring the uniform dispersion of the silver powder, the pre-alloying will ensure that the samples in the subsequent rapid hot pressing sintering and solution process are uniform and dense. In order to promote the full solution of silver elements in the copper matrix and further improve the densification level of the material, the composite material is solution quenched. The material is solution treated at 780°C for 1-3 hours, and then the material is cooled to room temperature by rapid quenching to make the silver uniformly dissolved in the copper matrix to form a stable solid solution structure. The solution treatment makes the Ag solution more uniform, ensuring that the excellent mechanical properties of the material remain uniform throughout the sample, which also ensures that the material will not partially fail and fall off during the electrical contact process, resulting in the failure to achieve the original life of the electrical contact.

[0020] (4) In actual electrical contact performance tests, the copper-silver-three-dimensional network graphene composite material of the present invention has a service life as an electrical contact that exceeds that of the commercial copper-silver material used in overhead contact lines for railway transportation. After electrical contact, its surface morphology is smoother, with fewer cracks, melting and oxidation, resulting in less quality loss, and the contact life exceeds that of most copper-silver contact materials. This demonstrates their superior ability to solve electrical contact challenges and abnormal wear phenomena in electrical engineering systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a flow chart of the preparation process of the present invention; Figure 2 This is a microscopic scanning electron microscope morphology image of the copper-silver / three-dimensional network graphene composite electrical contact material prepared in Example 1 of the present invention; Figure 3 The graphene surface scanning electron microscope morphology and transmission electron microscope thickness map under different acetylene flow rates; Figure 4 Raman spectra graphene quality map under different acetylene flow rates; Figure 5 Schematic diagrams of four types of contact pairs for electrical contact testing involved in Example 1 and Comparative Example 1 of the present invention; Figure 6 The surface scanning electron microscope morphology of the copper-silver-carbon and copper-silver graphene-carbon electrical contact pairs of the present invention, the EDSmapping element distribution diagram, the element content table and the mass loss before and after electrical contact and the contact life statistics diagram; Figure 7 A schematic diagram of the mechanism of the three-dimensional network graphene of the present invention to improve the electrical contact performance; Figure 8 The scanning electron microscope image and EDSmapping element distribution diagram of the pre-alloying phenomenon of copper and silver powders after low-energy ball milling mixing of the present invention. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below in conjunction with specific examples and comparative examples, which are provided only to illustrate the present invention, but not to limit the scope of the present invention. The experimental methods in the following examples are conventional methods unless otherwise specified; the materials, reagents, instruments, etc. used are all commercially available unless otherwise specified.

[0023] See also Figure 1The preparation process of the present invention is as follows: first, in a chemical vapor deposition rotary tube furnace, hydrogen is used to reduce the copper oxide raw material powder. Due to the volume shrinkage effect in the reduction process, a uniform and fine porous structure can be formed inside the powder; then, a low-energy ball milling process is used to mix the porous copper powder with the silver powder to prepare a surface alloyed mixed powder; then, acetylene is used as a gas carbon source, and low-temperature chemical vapor deposition is performed in the mixed powder through an in-situ chemical vapor deposition method to introduce hydrogenated graphite. With the help of the porous structure, the gas can fully flow inside the pores and the hydrogenated graphite is uniformly deposited on the porous wall surface, so that the hydrogenated graphite accurately replicates the morphology of the porous skeleton; finally, through high-temperature rapid hot pressing sintering, solution quenching treatment, room temperature rolling and annealing treatment, a copper-silver-three-dimensional network graphene composite electrical contact material is successfully prepared.

[0024] The specific preparation steps include: (1) Reduction process of original copper oxide powder In the embodiment of the present invention, copper oxide powder with a particle size of 15 μm is used as the raw material, 50 g of copper oxide powder is weighed, accurately weighed using an electronic balance, and then fed into the constant temperature zone of the rotary chemical vapor deposition rotary tube furnace through a powder feeding rod. The temperature rise program is set, the temperature range of the reduction process is 200-400°C, the heating rate is set to 5-10°C / min, the holding time is 2-5 hours, and the rotation rate is controlled at 170-200 rpm.

[0025] Reduction temperature: When the temperature is lower than 200℃, the reduction of copper oxide is incomplete and a large amount of CuO particles remain. When the temperature is higher than 450℃, the reduced copper powder will sinter to form a large block structure, which is difficult to achieve uniform dispersion.

[0026] Insulation time: Insulation time less than 1 hour is not enough to completely reduce copper oxide. The preferred insulation time is 2-5 hours.

[0027] Rotation rate: Rotation speed that is too slow will cause powder to stick together, while rotation speed that is too fast may cause powder to splash out of the constant temperature zone of the furnace.

[0028] During the heating and insulation process, the rotary tube furnace rotates slowly at a constant speed to ensure sufficient and uniform contact between the powder and the gas. Before the experiment, 200 sccm of argon gas is introduced to clean the furnace tube for 10 minutes to remove air and other impurity gases in the tube to avoid adverse effects on the raw material powder. Then, hydrogen gas is introduced at the reduction temperature and the temperature is maintained to ensure that the copper oxide powder can be fully reduced to porous copper powder.

[0029] (2) Mechanical mixing of Cu and Ag powders by low-energy ball milling Porous copper powder (40 g) and silver powder (0.048 g) were placed in a 250 mL stainless steel ball mill according to a certain ball-to-material ratio (10:1, using a 6 mm diameter steel ball), filled with argon as a protective gas, and then mechanically mixed using a planetary ball mill at a speed of 200 rpm. After mixing for 1-2 hours, a Cu and Ag mixed powder was obtained.

[0030] (3) Deposition process of hydrogenated graphite Loading and pretreatment: Place the mixed powder into the constant temperature zone of the rotary chemical vapor deposition furnace to ensure uniform distribution of the powder. Set the heating program with a heating rate of 5-10°C / min and a rotation rate of 170-200 rpm. To ensure the purity of the experimental environment, 200 sccm of argon gas was introduced to clean the furnace tube for 10 minutes before the experiment to remove air and other impurities in the tube to prevent adverse effects on the raw materials.

[0031] Gas introduction: After cleaning, a mixed gas of argon, hydrogen and acetylene is introduced, with the gas flow ratio of argon (500): hydrogen (200): acetylene (10, 20, 30) sccm. This ratio design ensures that the deposition environment has sufficient reducing properties and carbon source supply capacity.

[0032] Deposition process parameters: temperature 200℃-400℃ (low temperature conditions), time 10-15 minutes. Under this condition, acetylene is used as a carbon source to generate hydrogenated graphite on the surface of the mixed powder through chemical vapor deposition reaction.

[0033] Deposition process control: During the deposition process, the rotating furnace tube moves at a constant speed to ensure that the gas flows evenly in the furnace and fully contacts the mixed powder. The hydrogenated graphite is evenly covered on the powder surface, gradually forming a complete and continuous hydrogenated graphite structure layer.

[0034] (4) Rapid hot pressing sintering process and growth of three-dimensional network graphene Mold preparation: Select a circular graphite mold with a diameter of φ30 mm, and cover the inner wall of the mold with cut graphite paper in advance to prevent material adhesion. After the mold is assembled, lay two pieces of cut φ30 mm graphite paper on the gasket at the bottom of the mold to facilitate subsequent demolding and sampling operations.

[0035] Powder filling: Pour the composite powder evenly into the mold, then lay another two pieces of φ30 mm graphite paper on top of the powder, and install the upper ejector of the mold to ensure that the mold is sealed firmly.

[0036] Sintering process: send the assembled mold into the rapid hot pressing sintering work area, close the hatch, and turn on the cooling water, hydraulic system and heating power supply.

[0037] Set the heating program: pressure 30-50 MPa, temperature 750-800℃, heating and pressure rise time 5-10 minutes, heat and pressure holding time 5-10 minutes. During the heating and pressure rise period, ensure that the temperature and pressure are applied evenly to avoid local overheating or stress concentration.

[0038] Cooling and demoulding: After the heat preservation and pressure maintenance is completed, stop heating, wait for the mold to cool naturally to a safe temperature, and then take the graphite mold out of the sintering work area. When demoulding, the graphite mold should be carefully disassembled to ensure the integrity of the sample.

[0039] (5) Solution quenching, room temperature rolling and annealing process Solution quenching: In order to promote the full solution of silver elements in the copper matrix and further improve the densification level of the material, the composite material is subjected to solution treatment. The material is solution treated at 780°C for 1-3 hours, and then the material is cooled to room temperature by rapid quenching to uniformly dissolve silver in the copper matrix and form a stable solid solution structure.

[0040] Room temperature rolling; after solution treatment, the sample surface and edges are polished to remove excess flash and residual graphite paper traces to ensure the surface quality and accuracy of the rolling process. During the rolling process, the deformation of a single rolling pass is controlled at 5%, and the final total deformation reaches 50%. After multiple passes of room temperature rolling, the sample thickness is finally controlled at 2 mm to form a thin sheet specimen.

[0041] Annealing treatment: The rolled thin sheet samples are placed in a box-type resistance furnace for annealing treatment to eliminate the residual stress introduced during room temperature rolling and improve the mechanical properties of the material. The annealing temperature is set at 200-350℃ and the holding time is 1-3 hours to ensure that the internal stress of the material is completely released while maintaining the uniformity and stability of the microstructure.

[0042] (6) Composite electrical contact material performance test The tensile properties, Vickers hardness and conductivity of the samples were tested using an electronic universal testing machine, a Vickers microhardness tester and an eddy current conductivity meter. The electrical contact performance of the material was tested using an electrical contact tester built in the laboratory. The commercial copper-silver contact wire material CuAg-CTA150 used in the embodiment of the present invention has an element content as shown in Table 1: Table 1 Element content of commercial copper-silver contact wire material CuAg-CTA150

[0043] The copper-impregnated carbon slide plate material MY258A2 used in the electrical contact pair of the embodiment of the present invention has an element content as shown in Table 2: Table 2 Element content of copper-impregnated carbon slide material MY258A2

[0044] The parameters of the electrical contact test instrument are as follows: Ambient air: 18~22℃, humidity 20~40% Operating frequency: 0.5 Hz (1 second on, 1 second off) Initial contact distance: 150 mm Initial contact force: 3.5 N Contact moving speed: 150 mm / s Applied voltage: 24 V Applied current: 24 A.

[0045] The specific preparation method is shown in the following examples.

[0046] Example 1

[0047] (1) Take copper oxide powder with a particle size of 5 μm as the raw material, weigh 50g of copper oxide powder, accurately weigh it using an electronic balance, and then feed it into the constant temperature zone of the rotary chemical vapor deposition rotary tube furnace through the powder feeding rod. Set the heating program, the temperature range of the reduction process is 200-400℃, the heating rate is set to 5-10℃ / min, the insulation time is 2-5 hours, and the rotation rate is controlled at 170-200 rpm. During the heating and insulation process, the rotary tube furnace rotates slowly at a uniform speed to ensure sufficient and uniform contact between the powder and the gas. Before the experiment starts, 200 sccm of argon gas is introduced to clean the furnace tube for 10 minutes to remove air and other impurity gases in the tube to avoid adverse effects on the raw material powder. Then, hydrogen is introduced at the reduction temperature and the temperature is kept for reduction to ensure that the copper oxide powder can be fully reduced to porous copper powder.

[0048] (2) Porous copper powder (40 g) and silver powder (0.048 g) were placed in a 250 mL stainless steel ball mill according to a certain ball-to-material ratio (10:1, using a 6 mm diameter steel ball). Argon was filled into the mill as a protective gas, and the powders were mechanically mixed using a planetary ball mill at a rotation speed of 200 rpm. After mixing for 1-2 h, a mixed powder was obtained.

[0049] (3) The mixed powder is placed in the constant temperature zone of a rotary chemical vapor deposition furnace. A heating program is set with a heating rate of 5-10°C / min and a rotation rate of 170-200 rpm. To ensure the purity of the experimental environment, 200 sccm of argon gas is introduced to clean the furnace tube for 10 minutes before the experiment to remove air and other impurities in the tube to prevent adverse effects on the raw materials. After cleaning, a mixed gas of argon, hydrogen and acetylene is introduced with a gas flow ratio of argon (500): hydrogen (200): acetylene (10) sccm. This ratio design enables the deposition environment to have sufficient reducing and carbon source supply capacity. The deposition process parameters are selected as temperature: 200°C (low temperature conditions) and time: 10-15 minutes. Under these conditions, acetylene is used as a carbon source to generate hydrogenated graphite on the surface of the mixed powder through a chemical vapor deposition reaction. During the deposition process, the rotating furnace tube moves at a uniform speed to ensure that the gas flows evenly in the furnace and is in full contact with the mixed powder. The hydrogenated graphite is evenly covered on the powder surface, gradually forming a complete and continuous hydrogenated graphite structure layer.

[0050] (4) Select a circular graphite mold with a diameter of φ30 mm, and wrap the inner wall of the mold with cut graphite paper in advance to prevent material adhesion. After the mold is assembled, lay two pieces of cut φ30 mm graphite paper on the gasket at the bottom of the mold to facilitate subsequent demolding and sampling operations. Pour the composite powder evenly into the mold, then lay another two pieces of φ30 mm graphite paper on top of the powder, and install the upper ejector of the mold to ensure that the mold is sealed firmly. Send the assembled mold to the rapid hot pressing sintering work area, close the hatch, and turn on the cooling water, hydraulic system and heating power supply. Set the heating program as follows: pressure: 30-50 MPa, temperature: 750-800℃, heating and pressure time: 5-10 minutes, and heat preservation and pressure time: 5-10 minutes. During the heating and pressure period, ensure that the temperature and pressure are applied evenly to avoid local overheating or stress concentration. After the heat preservation and pressure are completed, stop heating, wait for the mold to cool naturally to a safe temperature, and then remove the graphite mold from the sintering work area. When demolding, the graphite mold should be disassembled carefully to ensure the integrity of the sample.

[0051] (5) In order to promote the full solid solution of silver elements in the copper matrix and further improve the densification level of the material, the composite material was solution treated. The material was solution treated at 780°C for 1-3 hours, and then the material was cooled to room temperature by rapid quenching to make the silver uniformly dissolved in the copper matrix to form a stable solid solution structure. After solution treatment, the surface and edge of the sample were polished to remove excess burrs and residual graphite paper traces to ensure the surface quality and accuracy of the rolling process. During the rolling process, the deformation of a single rolling pass was controlled at 5%, and the final total deformation reached 50%. After multiple passes of room temperature rolling, the sample thickness was finally controlled at 2 mm to form a thin sheet specimen.

[0052] (6) The tensile properties, Vickers hardness and conductivity of the samples were tested using an electronic universal testing machine, Vickers microhardness tester and eddy current conductivity meter. The electrical contact properties of the materials were tested using an electrical contact tester built in the laboratory.

[0053] See also Figure 4 , the quality of graphene was analyzed by Raman spectroscopy, and it was found that the intensity ratio of the characteristic peaks D and G of graphene was D / I G =0.75, indicating that the graphene is of high quality.

[0054] Figure 2 This is the microscopic scanning electron microscope morphology of the copper-silver / three-dimensional network graphene composite electrical contact material prepared in this example. It can be seen from the figure that after the surface of the material is corroded, the graphene network is exposed relatively completely. It is found that the graphene network has a good structure, a fine and uniform grid, and a small grain size. The dense and structurally complete graphene network and fine grains have a good strengthening effect on the basic mechanical properties and electrical contact properties of the material.

[0055] After testing, the yield strength can reach up to 374MPa, the tensile strength can reach up to 425MPa, the elongation can reach 9.7%, the Vickers microhardness can reach 178HV, and the conductivity can reach 54.7 MS / m (94.3%IACS). Figure 5 As shown in (c), the contact life of the copper-silver graphene-carbon electrical contact pair can reach 332 times. Figure 5 As described in (b), the contact life of the copper-silver graphene-copper-silver graphene electrical contact pair can reach 821 times.

[0056] In order to verify the thermal stability of the composite material, this embodiment further performs annealing on the composite material after step (5): the rolled thin sheet sample is placed in a box-type resistance furnace for annealing to eliminate the residual stress introduced during the room temperature rolling process and improve the mechanical properties of the material. The annealing temperature is set to 300°C and the holding time is 1-3 hours to ensure that the internal stress of the material is completely released while maintaining the uniformity and stability of the microstructure.

[0057] According to the test, after annealing, the yield strength can reach up to 369MPa, the tensile strength can reach up to 420MPa, the elongation can reach 10.2%, the Vickers microhardness can reach 176HV, and the conductivity can reach 55.4MS / m (95.5%IACS). Since the material selected under actual working conditions is in a cold state, the material has not been tested for electrical contact life.

[0058] After annealing, the mechanical properties of the composite material did not change significantly, indicating that the thermal stability of the composite material is good, so annealing is not a necessary step. At the same time, due to the high temperature and long-term element diffusion during the annealing process, the grains of the traditional material will grow, and the internal dislocations will further dissipate, but due to the good solid solution strengthening effect of silver in the copper-silver / graphene material of this embodiment, the dislocations are significantly pinned and restricted, and the presence of network graphene further limits the movement of dislocations and the growth of grains at the grain boundaries and in the crystals, resulting in the material having good thermal stability.

[0059] Example 2

[0060] The preparation process is the same as that of Example 1, except that after cleaning in step (3), a mixed gas of argon, hydrogen and acetylene is introduced, and the gas flow ratio is: argon (500): hydrogen (200): acetylene (20) sccm.

[0061] See also Figure 4 , it is observed that the graphene layer is thicker and has more defects, I D / I G =0.91. The contact life of the copper-silver graphene-carbon electrical contact pair prepared using this parameter can reach 308 times, and the contact life of the copper-silver graphene-copper-silver graphene electrical contact pair can reach 811 times.

[0062] Example 3

[0063] The preparation process is the same as that of Example 1, except that after cleaning in step (3), a mixed gas of argon, hydrogen and acetylene is introduced, and the gas flow ratio is: argon (500): hydrogen (200): acetylene (30) sccm.

[0064] See also Figure 4 , it is observed that the graphene layer is thicker and has more defects, I D / I G =0.92. The contact life of the copper-silver graphene-carbon electrical contact pair prepared using this parameter can reach 297 times, and the contact life of the copper-silver graphene-copper-silver graphene electrical contact pair can reach 805 times.

[0065] See also Figure 3 and Figure 4 ,in Figure 3 (a) and (b) correspond to Example 1, Figure 3 (c) and (d) correspond to Example 2, Figure 3(e) and (f) correspond to Example 3. Examples 1, 2, and 3 provide the best adaptation parameters by adjusting the different contents of acetylene. Under three different acetylene flow rates, large-area graphene can be successfully grown in situ on the template surface to achieve complete surface coverage. The thickness of the graphene layer gradually increases with the increase of acetylene flow rate. Raman spectroscopy further confirms that the graphene grown in situ on the copper powder surface shows slight defects, corresponding to the three acetylene flow rates. D / I G The values ​​are 0.75, 0.91 and 0.92, respectively. With the increase of acetylene flow rate, the graphene G peak shows an obvious red shift (moves to a lower wave number), which means that the number of oxygen-containing functional groups on the graphene surface gradually decreases. Although the presence of oxygen-containing functional groups on graphene hinders effective interlayer welding, previous studies have shown that higher oxygen content helps to form strong Cu-OC interface bonds. At the same time, the weakening of the adhesion between graphene layers promotes interlayer sliding and thinning during rolling deformation, providing an additional mechanism for improving mechanical properties. In addition to the main spectral band, there are several combined bands in the range of 2500-3000 cm⁻¹ that are related to non-planar graphene structures, which can be attributed to the characteristic peaks 2D, D+G and 2D′, respectively (the three characteristic peaks of graphene 2D, D+G and 2D′ represent the layer thickness and non-planar state of graphene, that is, the presence of some three-dimensional edge locations or edge exposed features). When the acetylene flow rate is 30 sccm, the intensity of the three characteristic peaks of graphene on the copper powder surface increases significantly, indicating that the graphene thickness increases and has more exposed three-dimensional non-planar graphene edges. Figure 3 Discrete graphene structures can be observed in (e), which may have an adverse effect on the interfacial bonding between the substrate and graphene. In summary, an acetylene flow rate of 10 sccm is the best choice for graphene preparation, achieving a balance between achieving high-quality graphene and maintaining robust interfacial bonding.

[0066] Comparative Example 1

[0067] See also Figure 5 In this comparative example, the performance of the commercial copper-silver contact wire material CuAg-CTA150 is compared with that of the copper-silver-three-dimensional network graphene composite material of Example 1 of the present invention.

[0068] (1) Please see Figure 5 In (a), a two-terminal commercial copper-silver contact wire material CuAg-CTA150 is used for electrical contact experiments. Its contact life is about 88 times, which is much lower than that of the copper-silver-three-dimensional network graphene composite material in Example 1 of the present invention. Figure 5 In (b), its contact life is about 821 times.

[0069] (2) Please see Figure 5 Middle (d) and Figure 6The service life shown in (e) is about 110 times of contact life when the commercial copper-silver contact wire material CuAg-CTA150 and the copper-impregnated carbon slide plate material MY258A2 are used for electrical contact experiments, which is much lower than the copper-silver-three-dimensional network graphene composite material prepared in Example 1 of the present invention. Figure 5 (c) and Figure 6 In (e), the service life is about 332 times. In actual working conditions, the copper-silver contact wire and the carbon slide plate are in electrical contact with each other in the matching pair of the subway rail transit catenary. The original intention of designing this material is to make it have more outstanding performance than traditional commercial materials under this working condition. Therefore, it is more in line with the actual engineering significance to use the copper-impregnated carbon slide plate material MY258A2 as a comparison to simulate the actual working conditions.

[0070] (3) The tensile properties, Vickers hardness and conductivity of the commercial copper-silver contact wire material CuAg-CTA150 sample were tested using an electronic universal testing machine, a Vickers microhardness tester and an eddy current conductivity meter. The yield strength can reach up to 238MPa, the tensile strength can reach up to 382MPa, the elongation can reach 6%, the Vickers microhardness can reach 153HV, and the conductivity can reach 56.1MS / m (96.7%IACS). The Vickers hardness, tensile strength and plasticity of the copper-silver-three-dimensional network graphene composite material prepared in Example 1 of the present invention are higher than those of the commercial copper-silver contact wire material.

[0071] See also Figure 6 In (a) and (b), it can be seen from the microscopic morphology that the copper-silver material without the addition of network graphene has more severe surface cracking, melting, and oxidation. At the same time, the carbon rods in contact with it fall off more and crack more obviously. See also Figure 6 In (c) and (d), it can be seen from the microscopic morphology that the surface of the copper-silver graphene composite rod is flatter after contact, with fewer and smaller pits, no obvious cracking, and a lower degree of oxidation. At the same time, the carbon rod in contact with it has less loss and a smoother surface.

[0072] See also Figure 6 In (c1) and (c2), it can be seen from the microscopic morphology that after contact, the surface can be found to have obvious network graphene exposed, which can be compared with Figure 7 Network graphene corresponds well to the advantageous mechanism of improving electrical contact performance.

[0073] Please see attached Figure 7 In (b), combined with the test data, it can be seen that the CuAg alloy without network graphene will produce very serious cracking, melting and oxidation after electrical contact. At the same time, the elements of the matrix and the elements on the carbon rod will be lost in large quantities, resulting in a large amount of mass loss and corrosion pits. Please refer to Figure 6The mass loss values ​​of (e) are 16.4 mg for CuAg-C and 2.2 mg for CuAg / graphene-C. Figure 6 The data in the table show that the discharge phenomenon is very intense and the transfer between materials is more. Figure 7 In (a), it can be found that after adding network graphene, due to the high melting point of graphene and its chemical inertness to arc ablation, when the arc is generated on the surface of the composite material, the electron density of the matrix is ​​higher than that of the graphene. Due to the low work function and melting point, the matrix region in the copper-silver-three-dimensional network graphene composite material will undergo arc ablation and evaporation before the graphene region. After the matrix evaporates, the remaining network graphene with sharp edges can act as a lightning rod. Due to the lightning rod effect of the sharp network graphene edge, graphene can focus and consume arc energy to further reduce the ablation and evaporation of the substrate region, and there is a self-passivation effect. No serious cracking, oxidation and melting state were found on the surface after contact. At the same time, due to the good support and strengthening effect of the network graphene on the substrate, the mass loss of the substrate is also less, and the surface of the carbon rod is smoother and there is less material transfer. This is the fundamental reason why the copper-silver-three-dimensional network graphene composite electrical contact material of the present invention has excellent electrical contact performance and life.

[0074] Comparative Example 2

[0075] The preparation process is the same as that of Example 1, except that step (2) is omitted, that is, the silver element is not introduced into the copper matrix. The prepared copper / three-dimensional network graphene sample is subjected to an electrical contact experiment, and its contact life is about 586 times, which is lower than the copper-silver-three-dimensional network graphene composite material in Example 1 of the present invention (821 times).

[0076] The tensile properties, Vickers hardness and conductivity of the copper / three-dimensional network graphene sample were tested using an electronic universal testing machine, a Vickers microhardness tester and an eddy current conductivity meter. The yield strength can reach up to 210MPa, the tensile strength can reach up to 375MPa, the elongation can reach 7.1%, the Vickers microhardness can reach HV144, and the conductivity can reach 56.5MS / m (97.4% IACS). The Vickers hardness, tensile strength, contact life and plasticity of the copper-silver-three-dimensional network graphene composite material prepared in Example 1 of the present invention are all higher than those of the copper / three-dimensional network graphene material in the comparative example.

[0077] The invention can significantly improve the electrical contact performance of the composite material by introducing a very small amount of Ag into the pure copper substrate.

[0078] First of all, in the field of copper-silver electrical contact materials, the higher the silver content, the better the electrical contact performance and the longer the contact life, but silver is a precious metal, and a higher content means a higher cost. Therefore, under the premise of adding network graphene, achieving a very small amount of silver content can also achieve a higher contact life and significantly reduce costs.

[0079] Secondly, compared with ordinary pure copper-three-dimensional network graphene composite materials, in the copper-silver matrix, the role of silver is reflected in solid solution strengthening. Silver can be dissolved in the copper matrix to improve the strength and hardness of the material. Considering the frequent switching of the circuit of the electrical contact point, strong wear resistance and hardness are indispensable for the practical application of electrical contact materials; silver has a high antioxidant capacity and is not easily oxidized at room temperature. It can effectively prevent the formation of an oxide film on the surface of the contact point, thereby avoiding problems such as increased contact resistance and unstable electrical signals caused by the oxide film; silver is a highly conductive element (conductivity 108.6% IACS). This feature enables silver-containing electrical contact materials to efficiently transmit current, reduce power loss, and ensure stable transmission of electrical signals; silver has a low and stable contact resistance. Low contact resistance helps to reduce the loss of power in the line and improve the energy efficiency of the equipment. At the same time, it can also ensure the smooth flow of current and avoid equipment failures caused by poor contact; silver has excellent arc tolerance and arc erosion resistance. During the on-off process of electrical equipment, the generation of arcs will cause erosion and damage to electrical contact materials. Silver-containing electrical contact materials have good resistance to arc erosion and can maintain a relatively stable structure and performance under the action of an arc, thereby reducing material loss and extending the service life of electrical contact components. The high electrical conductivity and thermal conductivity of silver help to quickly disperse the heat generated by the arc and reduce the energy density of the arc, thereby reducing the destructive effect of the arc on the contact points and improving the reliability of electrical contact materials under high voltage and high current conditions.

[0080] In addition, there is an interaction between silver and graphene: silver has high wettability and can form a good interface with the graphene surface. Silver atoms may attach to graphene through chemical bonds or van der Waals forces, thereby improving the interfacial bonding of the overall composite material. Silver can be used as a surface modifier to improve the dispersion of graphene through chemical reactions or physical adsorption, thereby avoiding the agglomeration of graphene in the copper-silver matrix. Silver has excellent electrical conductivity, and its combination with graphene can improve the electron transmission capacity of the composite material. Silver can fill the conductive path between graphene and the copper matrix and improve the overall conductive efficiency. The high thermal conductivity of silver and graphene complement each other, so that the composite material exhibits excellent thermal conductivity, especially in electrical contact devices, which can effectively dissipate heat. In some cases, silver can prevent the oxidation of graphene and protect the network structure of graphene, thereby improving the stability of the material. The presence of silver can reduce interface defects, combined with the excellent slip of graphene, so that the wear resistance and flexibility of the composite material are improved.

[0081] Comparative Example 3

[0082] The preparation process is the same as that of Example 1, except that high-energy ball milling (400 rpm, for 1-2 h) is used instead of low-energy ball milling in step (2). The prepared copper-silver graphene sample is subjected to an electrical contact experiment, and its contact life is about 412 times, which is lower than that of the copper-silver-three-dimensional network graphene composite material obtained by low-energy ball milling (821 times).

[0083] Since high-energy ball milling has high energy, it will smash the ground powder, resulting in the destruction of the skeleton structure of porous copper, which will cause a certain degree of damage to the three-dimensional network structure of graphene and reduce the electrical contact life. Figure 8 As shown, due to the mechanical action during mixing, part of the surface of the copper powder and the Ag powder will be pre-alloyed, and there will be a preliminary surface bonding between the different types of powders. While ensuring the uniform dispersion of the Ag powder, the pre-alloying will ensure that the samples in the subsequent rapid hot pressing sintering and solid solution process are uniform and dense.

[0084] Comparative Example 4

[0085] The preparation process is the same as that of Example 1, except that step (5) is omitted, that is, no solution quenching treatment is performed, and the tensile properties, Vickers hardness and conductivity of the sample are tested using an electronic universal testing machine, a Vickers microhardness tester and an eddy current conductivity meter. Its yield strength reaches 312 MPa, its tensile strength reaches 398 MPa, its hardness reaches HV149, its elongation can reach 5.4%, its conductivity can reach 54.1 MS / m (93.3% IACS), and its contact life is about 765 times, which is lower than the copper-silver-three-dimensional network graphene composite material (821 times) treated by solution quenching in Example 1.

[0086] By comparison, it was found that solution quenching treatment can effectively dissolve silver elements into the copper matrix, enhance the stability of the material, strengthen the interface bonding between graphene and silver, enhance the mechanical properties, and significantly improve the contact life.

[0087] Comparative Example 5

[0088] The preparation process is the same as that of Example 1, except that in step (2), porous copper powder (40 g) and silver powder (2 g) are mixed, and in step (3), acetylene is not introduced, and finally a CuAg5 alloy material is obtained. The prepared sample is subjected to an electrical contact test, and its contact life is about 245 times, which is lower than that of the copper-silver-three-dimensional network graphene composite material (821 times).

[0089] The tensile properties, Vickers hardness and conductivity of the samples were tested using an electronic universal testing machine, a Vickers microhardness tester and an eddy current conductivity meter. The yield strength reached 413MPa, the tensile strength reached 524MPa, the hardness reached HV160, the elongation reached 3.7%, and the conductivity reached 53.6MS / m (92.4%IACS).

[0090] The research concept of the present invention is to achieve a higher electrical contact life based on a smaller silver content. The consensus of electrical contact materials is that the higher the silver content, the better the electrical contact life, but the addition of silver will lead to excessively high costs. The silver content of Example 1 is only 0.1wt%, while the silver content of this comparative example is 5wt%. It can be seen that, compared with conventional copper-silver alloy materials, the copper-silver / three-dimensional network graphene composite material prepared by the present invention can significantly improve the electrical contact life of the composite material with a very small amount of silver added.

[0091] Please refer to Table 3 for the mechanical properties, electrical conductivity and contact life parameters of the materials prepared in different embodiments and comparative examples of the present invention.

[0092] Table 3 Mechanical properties, electrical conductivity and contact life parameters of materials prepared in different embodiments and comparative examples

[0093] The present invention proposes a method for preparing a copper-silver-three-dimensional network graphene composite material by combining in-situ synthesis with low-energy ball milling. The present method facilitates the in-situ formation of a three-dimensional graphene network while ensuring effective powder mixing. The subsequent rapid hot pressing, solution quenching treatment, room temperature rolling and annealing treatment processes facilitate the dissolution of silver in the composite material and the formation of a three-dimensional graphene network. Compared with previously reported methods, the present method is very effective and very suitable for promoting large-scale production on an industrial scale. In actual electrical contact performance tests, the service life of our copper-silver-three-dimensional network graphene composite electrical contact materials as electrical contacts exceeded that of commercial copper-silver materials used in overhead contact lines for railway transportation. This demonstrates their superior ability to address electrical contact challenges and abnormal wear phenomena in electrical engineering systems.

[0094] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a copper-silver / three-dimensional network graphene composite electrical contact material, characterized in that: The following steps are involved: S1. Reduction of the original CuO powder: The CuO powder is fed into a constant temperature zone in a rotary chemical vapor deposition rotary tube furnace, hydrogen is introduced, a temperature rise program is set, and the CuO powder is reduced to obtain a porous copper powder; S2. Mechanically mix the Cu and Ag powders by low-energy ball milling: place the reduced porous copper powder and silver powder in a ball milling jar for low-energy ball milling, wherein the silver powder accounts for 0.01-0.2% of the total mass, to obtain a Cu and Ag mixed powder; S3, deposition of hydrogenated graphite: feeding the Cu and Ag mixed powders into a constant temperature zone in a rotary chemical vapor deposition tube furnace, introducing argon, hydrogen and acetylene gases, setting a temperature rise program, and depositing hydrogenated graphite on the surface of the mixed powder under low temperature conditions to obtain a copper-silver / hydrogenated graphite composite powder; S4, rapid hot pressing sintering and growth of three-dimensional network graphene: placing copper-silver / hydrogenated graphite composite powder into a mold, sending the assembled mold into the working area of ​​a vacuum rapid hot pressing sintering furnace, closing the hatch, adjusting the heating program, performing rapid hot pressing sintering, waiting for natural cooling, taking out the graphite mold for demolding, and obtaining a copper-silver / three-dimensional network graphene composite material with three-dimensional network graphene grown inside; S5, solution quenching treatment, room temperature rolling and annealing treatment: the copper-silver / three-dimensional network graphene composite material is subjected to solution quenching treatment, room temperature rolling and annealing treatment in sequence to obtain a copper-silver / three-dimensional network graphene composite electrical contact material.

2. The method for preparing a copper-silver / three-dimensional network graphene composite electrical contact material according to claim 1, characterized in that: The particle size of the CuO original powder in S1 is 0.1 μm-15 μm.

3. The method for preparing a copper-silver / three-dimensional network graphene composite electrical contact material according to claim 2, characterized in that: In the S1, the heating rate is 5-10°C / min, the reduction temperature is 200-400°C, the insulation time is 2-5h, and the rotation rate is 170-200 rpm.

4. The method for preparing a copper-silver / three-dimensional network graphene composite electrical contact material according to claim 1, characterized in that: The ball mill speed in S2 is 180-220 rpm, and the mixing time is 1-2 hours; the ball-to-material ratio of low-energy ball milling is 8-10:1, and steel balls with a diameter of 5-8 mm are used.

5. The method for preparing a copper-silver / three-dimensional network graphene composite electrical contact material according to claim 1, characterized in that: In the S3, the heating rate is 5-10°C / min, the rotation rate is 170-200 rpm, the temperature for depositing hydrogenated graphite at low temperature is 200°C-300°C, and the hydrogenated graphite deposition time is 5-15min.

6. The method for preparing a copper-silver / three-dimensional network graphene composite electrical contact material according to claim 5, characterized in that: During the S3 hydrogenated graphite deposition, the gas flow ratio of argon, hydrogen and acetylene is 300-500:100-200:5-50.

7. The method for preparing a copper-silver / three-dimensional network graphene composite electrical contact material according to claim 1, characterized in that: The rapid hot pressing sintering in S4 adopts a pressure of 30-50 MPa, a temperature of 750-900° C., a temperature and pressure rise time of 5-10 min, and a temperature and pressure holding time of 5-10 min.

8. The method for preparing a copper-silver / three-dimensional network graphene composite electrical contact material according to claim 1, characterized in that: The solution quenching treatment method in S5 is: subjecting the copper-silver / three-dimensional network graphene composite material to a solution treatment at 700-800° C. for 1-3 hours, and then cooling the composite material to room temperature by rapid quenching to uniformly dissolve the silver in the copper matrix to form a stable solid solution structure.

9. The method for preparing a copper-silver / three-dimensional network graphene composite electrical contact material according to claim 8, characterized in that: The composite material obtained in S5 is further subjected to annealing treatment, with the annealing temperature set at 200-350° C. and the holding time being 1-3 hours, to ensure that the internal stress of the material is completely released while maintaining the uniformity and stability of the microstructure.

10. The copper-silver / three-dimensional network graphene composite electrical contact material prepared according to the method according to any one of claims 1 to 9.

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