A copper-silver / three-dimensional network graphene composite electrical contact material and its preparation method

Abstract

The present invention discloses a copper-silver / three-dimensional network graphene composite electrical contact material and a preparation method thereof. First, the present invention reduces the copper oxide raw material powder with hydrogen. Due to the volume shrinkage effect during the reduction process, a uniform and fine porous structure can be formed inside the powder. Subsequently, a low-energy ball milling process is used to mix the porous copper powder and silver powder to prepare a surface alloyed mixed powder. Then, using acetylene as a gas carbon source, low-temperature chemical vapor deposition is carried out in the mixed powder by in-situ chemical vapor deposition method to introduce hydrogenated graphite. With the existence of the porous structure, the gas can fully flow inside the pores, and the hydrogenated graphite is uniformly deposited on the surface of the porous wall, 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, the copper-silver / three-dimensional network graphene composite electrical contact material is successfully prepared.

Description

Technical Field

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

[0002] With the progress of new energy technologies, electric vehicles, communication systems, and other electronic devices, the demand for electrical contacts with excellent performance, stability, and reliability is increasing because they play a key role in enabling and interrupting electric 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 excellent wear resistance. Given the high cost of silver-based materials, current research has 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 about 1.1 TPa, a tensile strength exceeding 130 GPa, and a carrier mobility as high as 2×10 5 cm 2 / (V·s)) as well as a high melting point and chemical inertness against arc ablation, which can not only effectively improve the mechanical properties but also have the potential to achieve high electrical contact performance in copper-silver-based composite materials. However, due to van der Waals force-driven agglomeration and the difference in density between the copper matrix (8.9 g / cm 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, a sliding current-carrying friction pair consisting of graphite blocks and copper materials, is widely used due to its excellent electrical 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 environmental humidity. It is reported that water molecules can form strong hydrogen bonds in the carbon interlayer, 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. H2O molecules can penetrate the graphene interlayer and passivate 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:

[0007] 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;

[0008] 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;

[0009] 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;

[0010] S4. Rapid hot pressing sintering and growth of three-dimensional network graphene: Put the copper-silver / hydrogenated graphite composite powder into a mold, send the loaded mold into the working area of a vacuum rapid hot pressing sintering furnace, close the hatch, adjust the heating program, carry out rapid hot pressing sintering, wait for natural cooling, then take out the graphite mold for demolding to obtain a copper-silver / three-dimensional network graphene composite material with three-dimensional network graphene grown inside.

[0011] S5. Solution quenching treatment, room temperature rolling and annealing treatment: To promote the full solution of silver elements in the copper matrix and further improve the densification level of the material, the above-mentioned 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.

[0012] Preferably, the particle size of the CuO raw powder in S1 is 0.1 μm - 15 μm.

[0013] Preferably, in S1, the heating rate is 5 - 10 °C / min, the reduction temperature is 200 - 400 °C, the holding time is 2 - 5 h, and the rotation rate is 170 - 200 rpm.

[0014] Preferably, in S2, the ball mill rotation speed is 180 - 220 rpm, 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.

[0015] 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 - 15 min.

[0016] Preferably, when depositing hydrogenated graphite in S3, the gas flow ratio of argon, hydrogen and acetylene gases is 300 - 500:100 - 200:5 - 50.

[0017] Preferably, in S4, the rapid hot pressing sintering uses a pressure of 30 - 50 MPa, a temperature of 750 - 900 °C, a heating and pressure increasing time of 5 - 10 min, and a holding and pressure maintaining time of 5 - 10 min.

[0018] Preferably, the solution quenching treatment method in S5 is: Carry out solution treatment on the copper-silver / three-dimensional network graphene composite material at 700 - 800 °C for 1 - 3 hours, and then cool the composite material to room temperature by rapid quenching to make silver uniformly dissolve in the copper matrix to form a stable solid solution structure.

[0019] Preferably, the composite material obtained in S5 is further annealed. The annealing temperature is set at 200 - 350 °C, and the heat preservation 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.

[0020] Another object of the present invention is to provide a three-dimensional network copper-silver / three-dimensional network graphene composite electrical contact material prepared by the method according to the above.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] (1) The present invention prepares copper-silver-graphene composite powder by the method of in-situ synthesis plus low-energy ball milling. This method helps to in-situ form a three-dimensional graphene network and ensures effective powder mixing. The subsequent high-temperature rapid hot pressing, solution quenching, room-temperature rolling and annealing processes contribute to the solid solution of silver in the composite material and the formation of a three-dimensional graphene network. These advantages synergistically improve the mechanical properties of the material. The yield strength can reach up to 374 MPa at most, the tensile strength can reach up to 425 MPa at most, the elongation rate can reach 9.7%, the Vickers microhardness can reach HV178, and it has good thermal stability. The comprehensive performance has a major breakthrough compared with commercial copper-silver alloys.

[0023] (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 higher the contact life. However, silver is a precious metal, and a higher content means a higher cost. Under the premise of adding network graphene, the present invention 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 base material, the role of silver is solid solution strengthening. Silver can be solid-solved in the copper matrix, improving the strength and hardness of the composite material. In addition, there is an interaction between silver and graphene. Silver has high wettability and can form a good interfacial bond with the graphene surface, thus enhancing the stability of the material. The presence of silver can reduce interfacial defects. Combining with the excellent slip properties of graphene, the wear resistance and flexibility of the composite material are improved.

[0024] (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 the low-energy ball milling method. Due to the mechanical action during mixing, partial surface pre-alloying occurs between the copper powder and silver powder. There will be a preliminary surface bonding between different types of powders, ensuring the uniform dispersion of silver powder. At the same time, pre-alloying will ensure the uniform densification of the samples during subsequent rapid hot pressing sintering and solution processes. 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 quenching treatment. The material is solution-treated at 780 °C for 1 - 3 hours, and then cooled to room temperature by rapid quenching, enabling silver to be 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 are maintained uniformly throughout the sample, and thus ensuring that the material will not partially fail and fall off during the electrical contact process, resulting in the inability to reach the original service life of the electrical contact.

[0025] (4) In the actual electrical contact performance test, the copper-silver-three-dimensional network graphene composite material of the present invention, as an electrical contact, has a service life exceeding that of the commercial copper-silver material used in the overhead catenary of railway transportation. After electrical contact, its surface morphology is flatter, with fewer cracks, melting, and oxidation conditions, resulting in less mass loss, and the contact life exceeds that of most copper-silver contact materials. This proves their excellent ability to solve the electrical contact challenges and abnormal wear phenomena in electrical engineering systems. Brief Description of the Drawings

[0026] Figure 1 is the process flow chart of the preparation process of the present invention;

[0027] Figure 2 is the microscopic scanning electron microscope morphology diagram of the copper-silver / three-dimensional network graphene composite electrical contact material prepared in Example 1 of the present invention;

[0028] Figure 3 is the scanning electron microscope morphology on the surface of graphene and the transmission electron microscope thickness diagram at different acetylene flow rates;

[0029] Figure 4 is the Raman spectrum graphene quality diagram at different acetylene flow rates;

[0030] Figure 5 is the schematic diagram of the four electrical contact test contact pairs involved in Example 1 and Comparative Example 1 of the present invention;

[0031] Figure 6 is the surface scanning electron microscope morphology, EDS mapping element distribution diagram, element content table, and the statistical chart of mass loss and contact life before and after electrical contact of the copper-silver-carbon and copper-silver-graphene-carbon electrical contact pairs of the present invention;

[0032] Figure 7A schematic diagram of the mechanism of the three-dimensional network graphene of the present invention to improve the electrical contact performance;

[0033] Figure 8 The scanning electron microscope image and EDS mapping 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

[0034] 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.

[0035] See also Figure 1 The preparation process of the present invention is as follows: first, in a chemical vapor deposition rotary tube furnace, copper oxide raw material powder is reduced by hydrogen. Due to the volume shrinkage effect in the reduction process, a uniform and fine porous structure can be formed inside the powder; then, porous copper powder and silver powder are mixed by a low-energy ball milling process 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 by 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.

[0036] The specific preparation steps include:

[0037] (1) Reduction process of original copper oxide powder

[0038] 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.

[0039] 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.

[0040] Insulation time: An insulation time of less than 1 hour is not sufficient to fully reduce copper oxide. The preferred insulation time is 2 - 5 hours.

[0041] Rotation rate: If the rotation speed is too slow, the powder will adhere, and if it is too fast, the powder may splash out of the constant temperature zone of the furnace body.

[0042] During the heating and insulation processes, 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 starts, first introduce 200 sccm of argon to purge the furnace tube for 10 minutes to remove the air and other impurity gases inside the tube and avoid adverse effects on the raw material powder. Subsequently, introduce hydrogen at the reduction temperature and maintain the temperature for reduction to ensure that the copper oxide powder can be fully reduced to porous copper powder.

[0043] (2) Mechanically mix Cu and Ag powders by low-energy ball milling

[0044] Place the porous copper powder (40 g) and silver powder (0.048 g) in a 250 mL stainless steel ball milling jar according to a certain ball-to-material ratio (10:1, using 6 mm diameter steel balls), fill it with argon as the protective gas, and then use a planetary ball mill to mechanically mix the powders at a rotation speed of 200 rpm. After mixing for 1 - 2 hours, a Cu-Ag mixed powder is obtained.

[0045] (3) Deposition process of hydrogenated graphite

[0046] Loading and pretreatment: Put 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 the rotation rate controlled at 170 - 200 rpm. To ensure the purity of the experimental environment, introduce 200 sccm of argon to purge the furnace tube for 10 minutes before the experiment starts to remove the air and other impurity gases inside the tube and prevent adverse effects on the raw materials.

[0047] Gas introduction: After cleaning, introduce a mixed gas of argon, hydrogen, and acetylene. The gas flow ratio is: argon (500): hydrogen (200): acetylene (10, 20, 30) sccm. This ratio design enables the deposition environment to have sufficient reducibility and carbon source supply capacity.

[0048] Deposition process parameters: Temperature 200 °C - 400 °C (low temperature condition), time 10 - 15 minutes. Under these conditions, acetylene serves as the carbon source to generate hydrogenated graphite on the surface of the mixed powder through chemical vapor deposition reaction.

[0049] Deposition process control: During the deposition process, the rotary furnace tube moves at a constant speed to ensure uniform gas flow in the furnace and sufficient contact with the mixed powder. The hydrogenated graphite evenly covers the surface of the powder and gradually forms a complete and continuous hydrogenated graphite structure layer.

[0050] (4) Rapid hot pressing sintering process and growth of three-dimensional network graphene

[0051] Die preparation: Select a circular graphite die with a diameter of φ30 mm. Wrap the inner wall of the die with cut graphite paper in advance to prevent material adhesion. After assembling the die, lay two pieces of cut φ30 mm graphite paper on the gasket at the bottom of the die for subsequent demoulding and sampling operations.

[0052] Powder filling: Pour the composite powder evenly into the die, then lay another two pieces of φ30 mm graphite paper on top of the powder, and install the upper ejector rod of the die to ensure the die is sealed and stable.

[0053] Sintering process: Send the assembled die into the rapid hot pressing sintering working area, close the hatch, and turn on the cooling water, hydraulic system, and heating power supply.

[0054] Set the heating-up program: Pressure 30 - 50 MPa, temperature 750 - 800 °C, heating-up and pressure-increasing time 5 - 10 minutes, heat preservation and pressure-holding time 5 - 10 minutes. During the heating-up and pressure-increasing period, ensure uniform application of temperature and pressure to avoid local overheating or stress concentration.

[0055] Cooling and demoulding: After the heat preservation and pressure-holding are completed, stop heating. After the die naturally cools to a safe temperature, take out the graphite die from the sintering working area. When demoulding, carefully disassemble the graphite die to ensure the integrity of the sample.

[0056] (5) Solution quenching treatment, room temperature rolling and annealing treatment process

[0057] Solution quenching: 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 cooled to room temperature by rapid quenching to make silver evenly dissolve in the copper matrix to form a stable solid solution structure.

[0058] Room temperature rolling: After solution treatment, grind the surface and edges of the sample to remove excess flash and traces of residual graphite paper to ensure the surface quality and accuracy during the rolling process. During the rolling process, the deformation per single 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 flaky specimen.

[0059] Annealing treatment: The rolled thin sheet specimens were 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 was set at 200 - 350 °C, and the holding time was 1 - 3 hours to ensure complete release of the internal stress of the material while maintaining the uniformity and stability of the microstructure.

[0060] (6) Performance testing of the composite electrical contact material

[0061] The tensile properties, Vickers hardness, and electrical 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 self-built in the laboratory. The commercial copper-silver contact wire material CuAg-CTA150 used in the embodiments of the present invention has the elemental content shown in Table 1:

[0062] Table 1 Elemental content table of the commercial copper-silver contact wire material CuAg-CTA150

[0063]

[0064] The copper-impregnated carbon slide plate material MY258A2 selected for the electrical contact pair in the embodiments of the present invention has the elemental content shown in Table 2:

[0065] Table 2 Elemental content table of the copper-impregnated carbon slide plate material MY258A2

[0066]

[0067] The parameters of the electrical contact testing instrument are as follows:

[0068] Ambient air: 18 - 22 °C, humidity 20 - 40%

[0069] Operating frequency: 0.5 Hz (on for 1 second, off for 1 second)

[0070] Initial contact distance between contacts: 150 mm

[0071] Initial contact force: 3.5 N

[0072] Moving speed of the contacts: 150 mm / s

[0073] Applied voltage: 24 V

[0074] Applied current: 24 A.

[0075] For the specific preparation method, refer to the following examples.

[0076] Example 1

[0077] (1) Using copper oxide powder with a particle size of 5 μm as the raw material, weigh 50 g of copper oxide powder. After precise weighing using an electronic balance, feed it into the constant temperature zone of a rotary chemical vapor deposition rotary tube furnace through a powder feeding rod. Set the heating program. The temperature range during the reduction process is 200 - 400 °C, the heating rate is set at 5 - 10 °C / min, the holding time is 2 - 5 hours, and the rotation rate is controlled at 170 - 200 rpm. During the heating and holding processes, 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 starts, first introduce 200 sccm of argon to purge the furnace tube for 10 minutes to remove the air and other impurity gases inside the tube and avoid adverse effects on the raw material powder. Subsequently, introduce hydrogen at the reduction temperature and hold for reduction to ensure that the copper oxide powder can be fully reduced to porous copper powder.

[0078] (2) Place 40 g of porous copper powder and 0.048 g of silver powder in a 250 mL stainless steel ball milling jar according to a certain ball-to-material ratio (10:1, using 6 mm diameter steel balls), fill argon as the protective gas, and then use a planetary ball mill to mechanically mix the powder at a rotation speed of 200 rpm. After mixing for 1 - 2 h, a mixed powder is obtained.

[0079] (3) Put the mixed powder into the constant temperature zone of a rotary chemical vapor deposition furnace. Set the heating program with a heating rate of 5 - 10 °C / min and the rotation rate controlled at 170 - 200 rpm. To ensure the purity of the experimental environment, introduce 200 sccm of argon to purge the furnace tube for 10 minutes before the experiment starts to remove the air and other impurity gases inside the tube and prevent adverse effects on the raw materials. After cleaning, introduce a mixed gas of argon, hydrogen, and acetylene, and the gas flow ratio is: argon (500): hydrogen (200): acetylene (10) sccm. This ratio design enables the deposition environment to have sufficient reducing ability and carbon source supply capacity. The deposition process parameters are selected as temperature: 200 °C (low temperature condition), time: 10 - 15 minutes. Under these conditions, acetylene acts as a carbon source to generate hydrogenated graphite on the surface of the mixed powder through chemical vapor deposition reaction. During the deposition process, the rotary furnace tube moves at a constant speed to ensure uniform gas flow in the furnace and sufficient contact with the mixed powder. The hydrogenated graphite uniformly covers the surface of the powder and gradually forms a complete and continuous hydrogenated graphite structure layer.

[0080] (4)Select a circular graphite mold with a diameter of φ30 mm. Wrap the inner wall of the mold with cut graphite paper in advance to prevent material adhesion. After assembling the mold, lay two pieces of cut φ30 mm graphite paper on the gasket at the bottom of the mold for 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 rod of the mold to ensure the mold is sealed and stable. Send the assembled mold into the rapid hot pressing and sintering working 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 °C, heating and pressure increasing time: 5 - 10 minutes, heat preservation and pressure holding time: 5 - 10 minutes. During the heating and pressure increasing period, ensure that the temperature and pressure are applied evenly to avoid local overheating or stress concentration. After the heat preservation and pressure holding are completed, stop heating. After the mold naturally cools to a safe temperature, remove the graphite mold from the sintering working area. When demolding, carefully disassemble the graphite mold to ensure the integrity of the sample.

[0081] (5)To promote the full solid solution of silver elements in the copper matrix and further improve the densification level of the material, solution treatment is carried out on the composite material. The material is solution-treated at 780 °C for 1 - 3 hours, and then cooled to room temperature by rapid quenching to make silver uniformly solid-solved in the copper matrix, forming a stable solid solution structure. After solution treatment, grind the surface and edges of the sample to remove excess flash and residual graphite paper traces to ensure the surface quality and accuracy during the rolling process. During the rolling process, the deformation per pass is controlled at 5%, and the final total deformation reaches 50%. After multi-pass room temperature rolling, the sample thickness is finally controlled at 2 mm to form a flaky specimen.

[0082] (6)Use an electronic universal testing machine, Vickers microhardness tester, and eddy current conductivity meter to test the tensile properties, Vickers hardness, and conductivity of the sample. Use an electrically contacted tester self-built in the laboratory to test the electrical contact performance of the material.

[0083] Please refer to Figure 4 , use Raman spectroscopy to analyze the quality of graphene, and find that the intensity ratio I D / I G = 0.75, indicating that the quality of graphene is relatively high.

[0084] Figure 2Microscopic scanning electron microscope morphology diagram 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 more completely exposed. It is found that the graphene network structure is good, the grid is fine and uniform, and at the same time, the grain size is small. The dense and complete graphene network and the small grains play a good strengthening role in the basic mechanical properties and electrical contact properties of the material.

[0085] After testing, the yield strength can reach up to 374 MPa at most, the tensile strength can reach up to 425 MPa at most, the elongation can reach 9.7%, the Vickers microhardness can reach 178 HV, and the conductivity can reach 54.7 MS / m (94.3% IACS). As Figure 5 shown in (c) therein, the contact life of the copper-silver graphene-carbon electrical contact pair can reach 332 times. As Figure 5 described in (b) therein, the contact life of the copper-silver graphene-copper-silver graphene electrical contact pair can reach 821 times.

[0086] In order to verify the thermal stability of the above composite material, in this example, after step (5), the composite material is further annealed: the rolled sheet specimen 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 at 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.

[0087] After testing, after the annealing treatment, the yield strength can reach up to 369 MPa at most, the tensile strength can reach up to 420 MPa at most, the elongation can reach 10.2%, the Vickers microhardness can reach 176 HV, and the conductivity can reach 55.4 MS / m (95.5% IACS). Since the material selected under the actual working conditions is in the cold state, the electrical contact life test of this material is not carried out.

[0088] After the annealing treatment, the mechanical properties of the composite material do not change significantly, indicating that the composite material has good thermal stability. Therefore, the annealing treatment is not an essential step. At the same time, due to the high temperature and long-time element diffusion during the annealing process, the grains of traditional materials will grow, and the internal dislocations will further dissipate. However, due to the significant solid solution strengthening effect of silver in the copper-silver / graphene material of this example, the dislocations are significantly pinned and restricted, and the presence of the network graphene further restricts the movement of dislocations and the growth of grains synchronously at the grain boundaries and within the grains, resulting in the material having good thermal stability.

[0089] Example 2

[0090] The preparation process is the same as that of Example 1, except that after the 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.

[0091] Please refer to 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 with 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.

[0092] Example 3

[0093] The preparation process is the same as that of Example 1, except that after the 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.

[0094] Please refer to 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 with 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.

[0095] Please refer to Figure 3 and Figure 4 , where Figure 3 (a) and (b) in correspond to Example 1, Figure 3 (c) and (d) in correspond to Example 2, Figure 3 (e) and (f) in correspond to Example 3. Examples 1, 2, and 3 give the optimal matching parameters by regulating different contents of acetylene. At 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 the acetylene flow rate. Raman spectroscopy further confirms that the graphene grown in-situ on the copper powder surface shows slight defects, and the I D / I GThe values are 0.75, 0.91, and 0.92 respectively. As the acetylene flow rate increases, the G peak of graphene shows an obvious red shift (towards lower wavenumbers), 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 a higher oxygen content helps to form strong Cu-O-C interfacial bonds. At the same time, the weakening of the interlayer adhesion of graphene promotes interlayer sliding and thinning during the rolling deformation process, providing an additional mechanism for improving mechanical properties. In addition to the main spectral band, there are several combination bands in the range of 2500 - 3000 cm⁻¹ related to the non-planar graphene structure, which can be attributed to the characteristic peaks 2D, D+G, and 2D′ respectively (the three characteristic peaks 2D, D+G, and 2D′ of graphene represent the layer thickness and non-planar state of graphene, that is, the positions with some three-dimensional edges or the characteristics of exposed edges). When the acetylene flow rate is 30 sccm, the intensities of the three characteristic peaks of graphene on the copper powder surface increase significantly, indicating an increase in graphene thickness and more exposed three-dimensional non-planar graphene edges. Figure 3 In (e), discrete graphene structures can be observed, 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 obtaining high-quality graphene and maintaining a robust interfacial bond.

[0096] Comparative Example 1

[0097] Please refer to 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.

[0098] (1) Please refer to Figure 5 In (a), the commercial copper-silver contact wire material CuAg-CTA150 at both ends is used for the electrical contact experiment, and its contact life is about 88 times, which is much lower than that of the copper-silver-three-dimensional network graphene composite material of Example 1 of the present invention. Please refer to Figure 5 In (b), its contact life is about 821 times.

[0099] (2) Please refer to Figure 5 In (d) and Figure 6 the service life shown in (e), the commercial copper-silver contact wire material CuAg-CTA150 and the copper-impregnated carbon skateboard material MY258A2 are used for the electrical contact experiment, and its contact life is about 110 times, which is much lower than that of the copper-silver-three-dimensional network graphene composite material prepared in Example 1 of the present invention. Refer to Figure 5 In (c) and Figure 6In (e), the service life is about 332 times. Since in the actual working conditions, for the pantograph-catenary matching pair in subway rail transit, the copper-silver contact wire and the carbon skateboard are in an electrical contact state with each other, the original intention of designing this material is to make it have more prominent 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 skateboard material MY258A2 to simulate the actual working condition for comparison.

[0100] (3) Use an electronic universal testing machine, a Vickers microhardness tester, and an eddy current conductivity meter to test the tensile properties, Vickers hardness, and conductivity of the commercial copper-silver contact wire material CuAg-CTA150 sample. The yield strength can reach up to 238 MPa at most, the tensile strength can reach up to 382 MPa at most, the elongation rate can reach 6%, the Vickers microhardness can reach 153 HV, and the conductivity can reach 56.1 MS / 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 all higher than those of the commercial copper-silver contact wire material.

[0101] Please refer to Figure 6 In (a) and (b), it can be seen from the microscopic morphology diagrams that for the copper-silver material without adding network graphene, the surface cracking, melting, and oxidation are more serious. At the same time, more carbon rods in contact with it fall off, and the cracking is more obvious;

[0102] Please refer to Figure 6 In (c) and (d), it can be seen from the microscopic morphology diagrams that the surface of the copper-silver graphene composite material rod is flatter after contact, with fewer and smaller pits, no obvious cracking phenomenon, lower oxidation degree. At the same time, the loss of the carbon rod in contact with it is less, and the surface is smoother.

[0103] Please refer to Figure 6 In (c1) and (c2), it can be seen from the microscopic morphology diagrams that obvious network graphene can be found exposed on the surface after contact, which can correspond well to the advantage mechanism of network graphene in improving the electrical contact performance. Figure 7 The advantage mechanism of network graphene in enhancing the electrical contact performance corresponds well.

[0104] Please refer to the appendix Figure 7 In (b), and combined with the test data, it can be seen that for the CuAg alloy without network graphene, very serious cracking, melting, and oxidation phenomena will occur after electrical contact. At the same time, a large amount of elements in the matrix and on the carbon rod will be lost, resulting in a large amount of mass consumption and erosion pits. Please refer to Figure 6 In (e) for the mass loss values, it is 16.4 mg for CuAg-C, while it is 2.2 mg for CuAg / graphene-C. Please refer to the table data in the appendix Figure 6 In the appendix, the discharge phenomenon is very intense and there is more mutual transfer between the materials. While referring to the appendix Figure 7As can be seen from Fig. (a), after adding network graphene, due to the high melting point of graphene and its chemical inertness to arc ablation, when an arc is generated on the surface of the composite material, the electron density of the matrix is higher than that of graphene. Due to the lower 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 at the sharp edges of the network graphene, graphene can focus and consume the 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 states 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 less, and the surface of the carbon rod is flatter 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 lifespan.

[0105] Comparative Example 2

[0106] The preparation process is the same as that of Example 1, except that step (2) is cancelled, that is, 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 lifespan is about 586 times, which is lower than that of the copper-silver-three-dimensional network graphene composite material (821 times) in Example 1 of the present invention.

[0107] The tensile properties, Vickers microhardness, and electrical 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 210 MPa at most, the tensile strength can reach up to 375 MPa at most, the elongation rate can reach 7.1%, the Vickers microhardness can reach HV144, and the electrical conductivity can reach 56.5 MS / m (97.4% IACS). The Vickers microhardness, tensile strength, contact lifespan, 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 of this comparative example.

[0108] By introducing a very small amount of Ag into the pure copper substrate in the present invention, the electrical contact performance of the composite material can be significantly improved.

[0109] First of all, in the field of copper-silver electrical contact materials, the higher the silver content, the better its electrical contact performance and the higher the contact lifespan. However, silver belongs to precious metals, and a higher content means higher costs. Therefore, on the premise of adding network graphene, a very small amount of silver content can also achieve a higher contact lifespan and significantly reduce costs.

[0110] Secondly, compared with ordinary pure copper-three-dimensional network graphene composites, in the copper-silver base material, the role of silver is reflected in solid solution strengthening. Silver can be solid dissolved in the copper matrix, improving the strength and hardness of the material. Considering the frequent switching of circuits at the electrical contact point, strong wear resistance and hardness are essential for the practical application of electrical contact materials. Silver has a high oxidation resistance and is not easily oxidized at room temperature, which can effectively prevent the formation of an oxide film on the surface of the contact point, thus avoiding problems such as increased contact resistance and unstable electrical signals caused by the oxide film. Silver is a highly conductive element (electrical conductivity 108.6% IACS), and this property enables silver-containing electrical contact materials to efficiently transmit current, reduce power loss, and ensure the stable transmission of electrical signals. The contact resistance of silver is low and stable. A low contact resistance helps reduce power loss on the circuit, improve the energy efficiency of the device, and also ensure the smooth flow of current, avoiding 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 erode and damage the electrical contact materials. Silver-containing electrical contact materials have good arc erosion resistance performance, can maintain relatively stable structure and performance under the action of arcs, reduce material loss, and extend the service life of electrical contact components. The high electrical conductivity and thermal conductivity of silver help quickly disperse the heat generated by the arc, reduce the energy density of the arc, thereby reducing the destructive effect of the arc on the contact point and improving the reliability of electrical contact materials under high voltage and large current conditions.

[0111] In addition, there is an interaction between silver and graphene: Silver element has high wettability and can form a good interfacial bond with the graphene surface. Silver atoms may attach to graphene through chemical bonds or van der Waals forces, improving the interfacial bonding force of the overall composite material. Silver can act as a surface modifier to improve the dispersion of graphene through chemical reactions or physical adsorption, thus avoiding the agglomeration of graphene in the copper-silver matrix. Silver has excellent electrical conductivity, and its combination with graphene can improve the electron transport ability of the composite material. Silver can fill the conduction path between graphene and the copper matrix, improving the overall conduction efficiency. The high thermal conductivity of silver and graphene are complementary, making the composite material exhibit excellent thermal conduction performance, especially in electrical contact devices, where it can effectively dissipate heat. Silver can prevent the oxidation of graphene in some cases, protecting the network structure of graphene, thereby enhancing the stability of the material. The presence of silver can reduce interface defects, combined with the excellent slip properties of graphene, improving the wear resistance and flexibility of the composite material.

[0112] Comparative Example 3

[0113] The preparation process is the same as that of Example 1, except that in step (2), instead of low-energy ball milling, high-energy ball milling (400 rpm, for 1 - 2 h) is used. 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 prepared by low-energy ball milling (821 times).

[0114] Due to the relatively high energy of high-energy ball milling, the milled powder will be crushed, resulting in the destruction of the skeleton structure of porous copper, and the three-dimensional network structure of graphene will be damaged to a certain extent, leading to a reduction in the electrical contact life. And by using the low-energy ball milling method to mix porous copper powder and Ag powder, as Figure 8 shown, due to the mechanical action during mixing, the surfaces of some copper powder and Ag powder will be pre-alloyed. There will be a preliminary surface bonding between different types of powders, ensuring the uniform dispersion of Ag powder. At the same time, pre-alloying will ensure the uniform densification of the sample during subsequent rapid hot pressing sintering and solution treatment.

[0115] Comparative Example 4

[0116] The preparation process is the same as that of Example 1, except that step (5) is omitted, that is, solution quenching treatment is not carried out. The tensile properties, Vickers microhardness, and electrical 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, tensile strength reaches 398 MPa, hardness reaches HV149, elongation rate can reach 5.4%, and electrical conductivity can reach 54.1 MS / m (93.3% IACS). Its contact life is about 765 times, which is lower than that of the copper-silver-three-dimensional network graphene composite material with solution quenching treatment in Example 1 (821 times).

[0117] It is found by comparison that solution quenching treatment can effectively dissolve silver elements into the copper matrix, enhance the stability of the material, strengthen the interfacial bonding between graphene and silver, enhance the mechanical properties, and significantly improve the contact life.

[0118] Comparative Example 5

[0119] The preparation process is the same as that of Example 1, except that in step (2), porous copper powder (40 g) is mixed with silver powder (2 g), and in step (3), acetylene is not introduced. Finally, a CuAg5 alloy material is obtained. The prepared sample is subjected to an electrical contact experiment, 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).

[0120] The tensile properties, Vickers microhardness, and electrical 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 413 MPa, tensile strength reaches 524 MPa, hardness reaches HV160, elongation rate can reach 3.7%, and electrical conductivity can reach 53.6 MS / m (92.4% IACS).

[0121] The research concept of the present invention is to achieve a higher electrical contact life based on a relatively low silver content. The common understanding of electrical contact materials is that the higher the silver element content, the better the electrical contact life. However, the addition of silver elements will lead to too high costs. The silver content in Example 1 is only 0.1 wt%, while the silver content in this comparative example is 5 wt%. It can be seen that compared with the conventional copper-silver alloy materials, the extremely small silver addition amount of 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.

[0122] Please refer to Table 3 for the mechanical properties, electrical conductivity, and contact life parameters of the materials prepared in different examples and comparative examples of the present invention.

[0123] Table 3 Mechanical properties, electrical conductivity, and contact life parameters of materials prepared in different examples and comparative examples

[0124]

[0125] The present invention provides a method for preparing a copper-silver-three-dimensional network graphene composite material by combining in-situ synthesis and low-energy ball milling. This method helps to form a three-dimensional graphene network in-situ while ensuring effective powder mixing. The subsequent processes of rapid hot pressing, solution quenching treatment, room temperature rolling, and annealing treatment contribute to the dissolution of silver in the composite material and the formation of a three-dimensional graphene network. Compared with the methods reported by predecessors, this method is very effective and is 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 material as an electrical contact exceeds that of the commercial copper-silver materials used in overhead contact lines for railway transportation. This proves their excellent ability to solve the electrical contact challenges and abnormal wear phenomena in electrical engineering systems.

[0126] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. 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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