Graphene copper-based composite material, its preparation method and brake pads

Abstract

The present invention relates to a graphene copper-based composite material, a preparation method thereof, and a brake pad. The preparation method of the graphene copper-based composite material comprises the following steps: mixing a graphene slurry and a copper-based powder to obtain a powder; pressing the powder into a shape to obtain a green compact; subjecting the green compact to vacuum sintering to obtain a sintered compact; and subjecting the sintered compact to solution heat treatment and aging heat treatment to obtain the graphene copper-based composite material. This preparation method can produce a graphene copper-based composite material with high strength, high hardness, low wear amount, and high thermal conductivity.

Description

Technical Field

[0001] The present invention relates to the technical field of friction materials, and particularly to a graphene copper-based composite material, a preparation method thereof, and a brake pad. Background Art

[0002] With the rapid development of high-speed railways, the train braking system for ensuring driving safety at high speeds has attracted much attention. As a core component in the train braking system, the performance of the brake pad directly affects the safety and stability of train braking. With the continuous increase in train speed, the brake pads of trains require higher friction, excellent wear resistance, stable friction coefficient, good high-temperature resistance, and sufficient impact resistance, while being unaffected by the climate, having high economy, being easy to form, and achieving lightweight.

[0003] The brake pad materials of trains include asbestos friction materials, cast iron friction materials, powder metallurgy friction materials, etc. In recent years, copper-based powder metallurgy friction materials have become popular materials for developing high-performance brake pads due to their good wear resistance and thermal conductivity. In addition, graphene is a two-dimensional carbon nanomaterial with a honeycomb lattice structure composed of carbon atoms, possessing excellent mechanical properties and thermal conductivity. Combining graphene with copper-based powder to form a new composite material is beneficial to optimizing the performance of copper-based friction materials. However, due to the large density difference between graphene and copper-based powder, it is difficult to mix different components evenly, and the homogenization degree of the copper-based powder alloy after sintering is not high, and the contact between particles is poor, resulting in unsatisfactory strength, hardness, wear resistance, and thermal conductivity of the composite material. Summary of the Invention

[0004] Based on this, it is necessary to provide a graphene copper-based composite material with high strength, high hardness, low wear amount, and high thermal conductivity, a preparation method thereof, and a brake pad.

[0005] The above object of the present invention is achieved through the following technical solutions:

[0006] In the first aspect of the present invention, a preparation method of a graphene copper-based composite material is provided, including the following steps:

[0007] Mix a graphene slurry and copper-based powder to obtain a powder;

[0008] Press the powder into a mold to obtain a green compact;

[0009] Vacuum sinter the green compact to obtain a sintered compact;

[0010] Perform solution heat treatment and aging heat treatment on the sintered compact to obtain the graphene copper-based composite material.

[0011] In one embodiment, the solution heat treatment comprises the following steps: under a vacuum degree of ≤0.01 Pa, heating the green blank at 600°C to 800°C for 0.5 to 4 h, and then cooling to room temperature.

[0012] In one embodiment, the aging heat treatment comprises the following steps: under a vacuum degree of ≤0.01 Pa, heating the green blank after solution heat treatment at 200°C to 500°C for 0.5 to 4 h, and then cooling to room temperature.

[0013] In one embodiment, the vacuum sintering satisfies one or more of the following conditions:

[0014] 1) The sintering temperature is 800°C to 1000°C;

[0015] 2) The sintering time is 0.5 to 4 h;

[0016] 3) The vacuum degree is ≤0.01 Pa.

[0017] In one embodiment, the method of pressing and forming is one of cold isostatic pressing, hydrostatic forming, and die pressing.

[0018] In one embodiment, the cold isostatic pressing satisfies one or more of the following conditions:

[0019] 1) The maximum forming pressure is 100 MPa to 200 MPa;

[0020] 2) The pressure holding time is 10 min to 120 min.

[0021] In one embodiment, the graphene slurry comprises a solvent, graphene powder, and a dispersant.

[0022] In one embodiment, the graphene slurry satisfies one or more of the following conditions:

[0023] 1) The sheet diameter of the graphene powder is 0.1 to 5 μm;

[0024] 2) The solvent is water and / or ethanol;

[0025] 3) The dispersant is one or more of polyethylene glycol, polyvinyl alcohol, and ammonium polyacrylate;

[0026] 4) The mass ratio of the solvent, the graphene powder, and the dispersant is (75 to 95):(3 to 25):(0.5 to 5);

[0027] 5) The content of the graphene powder in the graphene copper-based composite material is 0.05 wt.% to 2 wt.%.

[0028] In one embodiment, the copper-based powder satisfies one or more of the following conditions:

[0029] 1) The chemical composition of the copper-based powder includes copper and one or more of the elements tin, zinc, iron, nickel, chromium, lead, phosphorus, bismuth, and silicon;

[0030] 2) The copper-based powder contains 75 wt.% to 92 wt.% of copper element;

[0031] 3) The copper-based powder contains 5 wt.% to 8 wt.% of tin element;

[0032] 4) The copper-based powder contains 2 wt.% to 8 wt.% of zinc element;

[0033] 5) The particle size of the copper-based powder is 0.1 μm to 100 μm.

[0034] In the second aspect of the present invention, a graphene copper-based composite material is provided, which is prepared by using the preparation method of the graphene copper-based composite material described above.

[0035] In the third aspect of the present invention, a brake pad is provided, which is prepared by subjecting the graphene copper-based composite material described above to surface treatment.

[0036] The present invention adopts solution heat treatment and aging heat treatment, combined with powder mixing, pressing molding, and vacuum sintering, to make the components of the composite material mix evenly and contact well, with a higher degree of alloy homogenization and densification, and realizes the dispersed distribution of graphene in the copper-based powder, thereby obtaining a graphene copper-based composite material with high strength, high hardness, low wear amount, and high thermal conductivity, effectively extending its service life. Description of the Drawings

[0037] Figure 1 SEM image of the graphene copper-based brake pad prepared for Example 2. Detailed Embodiments

[0038] In order to make the above objects, features, and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention will be given with reference to the drawings. Many specific details are set forth in the following description to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this invention belongs. The terms used in the description of this invention herein are for the purpose of describing specific embodiments only and are not intended to limit the invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0040] Terms and definitions:

[0041] Friction material: The component material that relies on friction to perform braking and transmission functions, has good friction coefficient and wear resistance, and at the same time has certain heat resistance and mechanical strength, and can be used to prepare brake pads.

[0042] Tensile strength: Tested with reference to "Metallic materials - Tensile testing - Part 1: Method of test at room temperature" (GB / T 228.1-2021); the tensile specimen is a round bar specimen with a diameter of 5 mm and a gauge length of 25 mm. The tensile properties of 3 specimens are detected for each group of experiments, and the average value is taken to record the data, with the unit of MPa; the larger the value, the higher the strength of the brake pad.

[0043] Hardness: Tested with reference to "Metallic materials - Vickers hardness test - Part 1: Test method" (GB / T 4340.1-2009); experiments are carried out using a Vickers hardness tester. The experimental load is 0.1 kg, the loading time is 10 s, 5 points are tested for each group of experiments, and the average value is taken to record the data, with the unit of HV; the larger the value, the higher the hardness of the brake pad.

[0044] Wear volume: Tested by reciprocating friction experiment. The counter - part is a GCr15 steel ball with a diameter of Φ5 mm, the test force is 50 N, the frequency is 5 Hz, the experimental size is 5 mm, the experimental time is 1 h. The wear volume of 3 specimens is detected for each group of experiments, and the average value is taken to record the data, with the unit of g; the smaller the value, the better the wear resistance of the brake pad and the longer the service life.

[0045] Thermal conductivity: Tested with reference to "Transient measurement of thermal conductivity and thermal diffusivity of materials - Pulse method" (DB51 / T 2434-2017), with the unit of W / (m·K); the larger the value, the better the thermal conductivity of the brake pad.

[0046] SEM: Scanning electron microscope.

[0047] In the first aspect of the present invention, a method for preparing a graphene - copper - based composite material is provided, including the following steps:

[0048] Mix graphene slurry and copper - based powder to obtain a powder.

[0049] Press the powder into a shape to obtain a green compact.

[0050] vacuum sintering the green body to obtain a cooked body;

[0051] The sintered body is subjected to solution heat treatment and aging heat treatment to obtain the graphene copper-based composite material.

[0052] The present invention adopts solution heat treatment and aging heat treatment, combined with powder mixing, pressing molding and vacuum sintering, so that the components of the composite material are evenly mixed and in good contact, the alloy has higher homogenization and density, and the graphene is dispersed in the copper-based powder, thereby obtaining a graphene copper-based composite material with high strength, high hardness, low wear and high thermal conductivity, effectively extending its service life.

[0053] In some embodiments, the solution heat treatment comprises the following steps: heating the slab at 600° C. to 800° C. for 0.5 to 4 hours under a vacuum degree of ≤0.01 Pa, and then cooling the slab to room temperature.

[0054] It can be understood that the temperature of the solution heat treatment can be any value between 600℃ and 800℃, such as 600℃, 650℃, 700℃, 750℃ or 800℃, etc., the heating time can be any value between 0.5 and 4h, such as 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h or 4h, etc., and the vacuum degree can be any value lower than 0.01Pa, such as 0.01Pa, 0.007Pa, 0.005Pa, 0.003Pa or 0.001Pa, etc.

[0055] It can be understood that room temperature refers to indoor temperature, normal temperature or general temperature, and the temperature range is 20℃~30℃.

[0056] In some embodiments, the cooling method is one of air cooling, water cooling, or oil cooling.

[0057] In some more preferred embodiments, the solution heat treatment comprises the following steps: heating the sintered blank at 600°C to 800°C for 0.5 to 4 hours under a vacuum degree of ≤0.01 Pa, and then cooling it to room temperature in water.

[0058] Solution heat treatment helps eliminate the large, unevenly distributed precipitates formed during vacuum sintering, allowing the copper powder and other metal powders to form a more uniform, supersaturated solid solution. It also removes thermal stresses generated during sintering and improves the toughness of the composite material. After heat treatment, water cooling is performed rapidly, allowing the supersaturated solid solution formed at high temperatures to remain as the temperature rapidly decreases, resulting in optimal solutionization.

[0059] In some embodiments, the aging heat treatment comprises the following steps: under a vacuum degree of ≤ 0.01 Pa, heating the solution heat-treated cured blank at 200°C to 500°C for 0.5 to 4 h, and then cooling to room temperature.

[0060] It can be understood that the temperature of the aging heat treatment can be any value between 200°C and 500°C, such as 200°C, 250°C, 300°C, 350°C, 400°C, 450°C or 500°C, etc., the heating time can be any value between 0.5 h and 4 h, such as 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h or 4 h, etc., and the vacuum degree can be any value lower than 0.01 Pa, such as 0.01 Pa, 0.007 Pa, 0.005 Pa, 0.003 Pa or 0.001 Pa, etc.

[0061] In some more preferred embodiments, the aging heat treatment comprises the following steps: under a vacuum degree of ≤ 0.01 Pa, heating the solution heat-treated cured blank at 200°C to 500°C for 0.5 to 4 h, and then cooling to room temperature in air.

[0062] Through the aging heat treatment, second-phase particles such as FeCr compounds are dispersed and precipitated on the copper matrix, achieving the purpose of precipitation strengthening, effectively improving the strength and hardness of the composite material, and thus reducing the wear amount during the friction process.

[0063] In some embodiments, the vacuum sintering satisfies one or more of the following conditions:

[0064] 1) The sintering temperature is 800°C to 1000°C;

[0065] 2) The sintering time is 0.5 to 4 h;

[0066] 3) The vacuum degree ≤ 0.01 Pa.

[0067] It can be understood that the sintering temperature can be any value between 800°C and 1000°C, such as 800°C, 850°C, 900°C, 950°C or 1000°C, etc., the sintering time can be any value between 0.5 h and 4 h, such as 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h or 4 h, etc., and the vacuum degree can be any value lower than 0.01 Pa, such as 0.01 Pa, 0.007 Pa, 0.005 Pa, 0.003 Pa or 0.001 Pa, etc.

[0068] High-temperature sintering under a certain vacuum degree can enable all gases in the green compact to escape from the pores, which is beneficial to reducing the number of pores, thereby improving the density and hardness of the material. At the same time, under the condition of extremely low vacuum degree, the contents of oxygen, nitrogen, hydrogen and water vapor are extremely small, and almost no chemical reaction occurs during the sintering process, which is beneficial to improving the purity of the composite material.

[0069] In some embodiments, the method of pressing and forming is one of cold isostatic pressing, hydraulic forming and die pressing.

[0070] The cold isostatic pressing satisfies one or more of the following conditions:

[0071] 1) The maximum forming pressure is 100 MPa to 200 MPa;

[0072] 2) The pressure holding time is 10 min to 120 min.

[0073] By cold isostatic pressing and forming, a green compact with uniform density and fewer pores can be obtained, which is beneficial to further improving the density and strength of the composite material.

[0074] In some embodiments, after mixing the graphene slurry and the copper-based powder evenly by powder mixing, it is dried and encapsulated.

[0075] In some embodiments, the powder mixing satisfies one or more of the following conditions: 1) The powder mixing time is 1 h to 6 h; 2) The rotation speed is 100 rpm to 300 rpm.

[0076] In some embodiments, the graphene slurry includes a solvent, graphene powder and a dispersant.

[0077] In some embodiments, the graphene slurry satisfies one or more of the following conditions:

[0078] 1) The sheet diameter of the graphene powder is 0.1 to 5 μm;

[0079] 2) The solvent is water and / or ethanol;

[0080] 3) The dispersant is one or more of polyethylene glycol, polyvinyl alcohol and ammonium polyacrylate;

[0081] 4) The mass ratio of the solvent, the graphene powder and the dispersant is (75 to 95):(3 to 25):(0.5 to 5);

[0082] 5) The content of the graphene powder in the graphene copper-based composite material is 0.05 wt.% to 2 wt.%.

[0083] After mixing the solvent, graphene powder and dispersant, a uniformly dispersed graphene slurry is obtained, which avoids the agglomeration of graphene during the powder mixing process, thereby realizing the dispersed distribution of graphene in the copper-based powder. The internal organizational structure of the composite material is more uniform and dense, and its mechanical strength and thermal conductivity are significantly improved. Controlling the content of graphene powder within 0.05 wt.% to 2 wt.% can also inhibit the agglomeration of graphene and make it easy to form during powder pressing.

[0084] In some embodiments, the copper-based powder satisfies one or more of the following conditions:

[0085] 1) The chemical composition of the copper-based powder includes copper, and one or more of the elements tin, zinc, iron, nickel, chromium, lead, phosphorus, bismuth, and silicon;

[0086] 2) The copper-based powder contains 75 wt.% to 92 wt.% of copper powder;

[0087] 3) The copper-based powder contains 5 wt.% to 8 wt.% of tin element;

[0088] 4) The copper-based powder contains 2 wt.% to 8 wt.% of zinc element;

[0089] 5) The particle size of the copper-based powder is 0.1 μm to 100 μm.

[0090] Adding elements such as tin, zinc, iron, nickel, chromium, lead, phosphorus, bismuth, and silicon to copper powder is beneficial to improving the strength, hardness, friction stability, and wear resistance of the copper matrix. Adding 2 wt.% to 8 wt.% of zinc element can improve the hardness, strength, and impact toughness of the copper-based powder, making it have good creep resistance and high-temperature resistance. Adding 5 wt.% to 8 wt.% of tin element can make the copper-based powder easily alloyed during vacuum sintering, making the copper-based powder have high heat resistance, strength, and hardness, and can prevent the adhesion of the friction pair surface during counter friction; the introduction of tin element is also beneficial to preventing dezincification phenomenon, thereby improving the corrosion resistance of the copper-based powder; when working at high temperature, adding tin will make the friction coefficient unstable, so graphene powder needs to be added to improve the heat resistance and friction performance to obtain a stable friction coefficient.

[0091] In some more preferred embodiments, the copper-based powder is made from the following raw materials in mass percentages: copper 77.55% to 91.34%, tin 5% to 8%, zinc 2% to 8%, iron 0.8% to 2%, nickel 0.8% to 3%, chromium ≤ 0.4%, lead ≤ 0.4%, phosphorus 0.03% to 0.35%, bismuth 0.02% to 0.2%, and silicon 0.01% to 0.1%.

[0092] In some more preferred embodiments, the copper-based powder is made of raw materials with the following mass percentages: copper 84.75%, tin 6%, zinc 5%, iron 1.5%, nickel 2%, chromium 0.2%, lead 0.2%, phosphorus 0.2%, bismuth 0.1% and silicon 0.05%;

[0093] In the second aspect of the present invention, a graphene copper-based composite material is provided, which is prepared by using the preparation method of the graphene copper-based composite material described above.

[0094] In the third aspect of the present invention, a brake pad is provided, which is obtained by surface-treating the graphene copper-based composite material described above.

[0095] In some more preferred embodiments, the graphene copper-based composite material described above is sandblasted and polished, and the sandblasting satisfies one or more of the following conditions: 1) the sandblasting air pressure is 0.2 MPa to 1.2 MPa; 2) the sandblasting time is 5 min to 20 min; 3) the shot is alumina ceramic.

[0096] The present invention will be further described in detail below with reference to specific embodiments.

[0097] Example 1

[0098] (1) Provide graphene slurry and copper-based powder:

[0099] The graphene slurry is made of raw materials with the following mass percentages: solvent 80%, graphene powder 15% and dispersant 5%; wherein, the solvent is ethanol, the dispersant is polyethylene glycol, and the sheet diameter of the graphene powder is 0.1 to 5 μm; to improve the dispersion of graphene, the above raw materials are mixed evenly by ultrasonic.

[0100] The copper-based powder is made of raw materials with the following mass percentages: copper 84.75%, tin 6%, zinc 5%, iron 1.5%, nickel 2%, chromium 0.2%, lead 0.2%, phosphorus 0.2%, bismuth 0.1% and silicon 0.05%; the particle size of the copper-based powder is 0.1 to 100 μm;

[0101] The content of graphene powder in the graphene copper-based composite material is 0.1 wt.%.

[0102] (2) Put the graphene slurry and the copper-based powder into a powder mixer and mix evenly. The powder mixing time is 4 h and the rotation speed is 200 rpm; then dry and encapsulate to obtain the powder.

[0103] (3) Load the powder into a special silica gel elastic mold and seal it; then put the powder-loaded mold into a cold isostatic pressing cylinder body, and perform powder pressing and forming through cold isostatic pressing. The maximum pressure is 150 MPa and the pressure holding time is 60 min to obtain a green blank.

[0104] (4) Put the green blank into a vacuum sintering furnace for sintering. The sintering temperature is 900 °C, the sintering time is 2 h, and the vacuum degree is ≤0.01 Pa; after sintering, it is cooled to room temperature with the furnace to obtain a mature blank.

[0105] (5) Put the mature blank into a vacuum heat treatment furnace for solution heat treatment and aging heat treatment to obtain a graphene copper matrix composite material; among them, the solution heat treatment includes the following steps: under a vacuum degree of ≤0.01 Pa, heat the above-mentioned mature blank to 700 °C, keep it warm for 2 h, and cool it to room temperature with water; the aging heat treatment includes the following steps: under a vacuum degree of ≤0.01 Pa, heat the mature blank after solution heat treatment to 400 °C, keep it warm for 2 h, and cool it to room temperature in air to obtain a graphene copper matrix composite material.

[0106] (6) First, perform surface treatment on the graphene copper matrix composite material with a sandblasting machine. The sandblasting air pressure is 0.6 MPa, the sandblasting time is 10 min, and the shot peening is Al2O3 ceramic; then use a grinding machine to polish its surface smoothly to obtain a graphene copper matrix brake pad.

[0107] (7) Performance test of the graphene copper matrix brake pad:

[0108] Test the tensile strength, Vickers hardness, wear amount, and thermal conductivity of the graphene copper matrix brake. The test results are shown in Table 1. It can be seen from Table 1 that the tensile strength of the graphene copper matrix brake pad is 690 MPa, the Vickers hardness is 216 HV, the wear amount is 0.0527 g, and the thermal conductivity is 407 W / (m·K), indicating that through the preparation process of powder mixing, cold isostatic pressing, vacuum sintering, solution heat treatment, and aging heat treatment, a graphene copper matrix brake pad with high strength, high hardness, low wear amount, and high thermal conductivity can be prepared.

[0109] Table 1. Performance test results of the brake pads prepared in Examples 1-9 and Comparative Examples 1-2

[0110]

[0111]

[0112] Example 2

[0113] The preparation method of this example is basically the same as that of Example 1, the difference is that: the content of graphene powder in the graphene copper matrix composite material is 0.5 wt.%.

[0114] Test the tensile strength, Vickers hardness, wear amount, and thermal conductivity of the graphene copper matrix brake. The test results are shown in Table 1. Perform SEM characterization on the graphene copper matrix brake pad, and the results are as Figure 1 shown.

[0115] FromFigure 1 It can be seen that the density and alloy homogenization degree of the graphene copper-based brake pads prepared by the preparation process of cold isostatic pressing, vacuum sintering, solution heat treatment and aging heat treatment are relatively high. As can be seen from Table 1, the tensile strength of the graphene copper-based brake pads is 754 MPa, the Vickers hardness is 243 HV, the wear amount is 0.0425 g, and the thermal conductivity is 435 W / (m·K), indicating that through the above preparation process, graphene copper-based brake pads with high strength, high hardness, low wear amount and high thermal conductivity can be prepared. Moreover, increasing the content of graphene powder is beneficial to improving the strength, hardness, wear resistance and thermal conductivity of the graphene copper-based brake pads.

[0116] Example 3

[0117] The preparation method of this example is basically the same as that of Example 1, the difference is that: the content of graphene powder in the graphene copper-based composite material is 1 wt.%. The tensile strength, Vickers hardness, wear amount and thermal conductivity of this graphene copper-based brake were tested, and the test results are shown in Table 1. As can be seen from Table 1, the tensile strength of the graphene copper-based brake pads is 897 MPa, the Vickers hardness is 282 HV, the wear amount is 0.0311 g, and the thermal conductivity is 482 W / (m·K), indicating that through the preparation process of powder mixing, cold isostatic pressing, vacuum sintering, solution heat treatment and aging heat treatment, graphene copper-based brake pads with high strength, high hardness, low wear amount and high thermal conductivity can be prepared. Moreover, increasing the content of graphene powder is beneficial to improving the strength, hardness, wear resistance and thermal conductivity of the graphene copper-based brake pads.

[0118] Example 4

[0119] The preparation method of this example is basically the same as that of Example 1, the difference is that: the content of graphene powder in the graphene copper-based composite material is 2 wt.%. The tensile strength, Vickers hardness, wear amount and thermal conductivity of this graphene copper-based brake were tested, and the test results are shown in Table 1. As can be seen from Table 1, the tensile strength of the graphene copper-based brake pads is 873 MPa, the Vickers hardness is 276 HV, the wear amount is 0.0366 g, and the thermal conductivity is 476 W / (m·K), indicating that through the preparation process of powder mixing, cold isostatic pressing, vacuum sintering, solution heat treatment and aging heat treatment, graphene copper-based brake pads with high strength, high hardness, low wear amount and high thermal conductivity can be prepared. Compared with Example 3, the strength, hardness, wear resistance and thermal conductivity of the graphene copper-based brake pads decreased slightly, but compared with Examples 1 and 2, their strength, hardness, wear resistance and thermal conductivity still increased significantly.

[0120] Example 5

[0121] This embodiment is basically the same as the preparation method of Embodiment 3, except that: when the powder is pressed into shape in step (3), the maximum pressure of cold isostatic pressing is 200 MPa and the pressure holding time is 30 min. The tensile strength, Vickers hardness, wear amount and thermal conductivity of this graphene copper-based brake are tested, and the test results are shown in Table 1. It can be seen from Table 1 that the tensile strength of the graphene copper-based brake pad is 862 MPa, the Vickers hardness is 261 HV, the wear amount is 0.0405 g, and the thermal conductivity is 472 W / (m·K), indicating that through the preparation process of powder mixing, cold isostatic pressing, vacuum sintering, solution heat treatment and aging heat treatment, under the condition of cold isostatic pressing with a maximum pressure of 200 MPa and a pressure holding time of 30 min, a graphene copper-based brake pad with high strength, high hardness, low wear amount and high thermal conductivity can also be prepared.

[0122] Example 6

[0123] This embodiment is basically the same as the preparation method of Embodiment 3, except that: when the green blank is subjected to vacuum sintering in step (4), the sintering temperature is 800 °C and the sintering time is 2 h. The tensile strength, Vickers hardness, wear amount and thermal conductivity of this graphene copper-based brake are tested, and the test results are shown in Table 1. It can be seen from Table 1 that the tensile strength of the graphene copper-based brake pad is 853 MPa, the Vickers hardness is 255 HV, the wear amount is 0.0411 g, and the thermal conductivity is 459 W / (m·K), indicating that through the preparation process of powder mixing, cold isostatic pressing, vacuum sintering, solution heat treatment and aging heat treatment, under the condition of vacuum sintering with a sintering temperature of 800 °C and a sintering time of 2 h, a graphene copper-based brake pad with high strength, high hardness, low wear amount and high thermal conductivity can also be prepared.

[0124] Example 7

[0125] This embodiment is basically the same as the preparation method of Embodiment 3, except that: when the semi-finished blank is subjected to solution heat treatment in step (5), the heating temperature is 600 °C and the heat preservation time is 2 h. The tensile strength, Vickers hardness, wear amount and thermal conductivity of this graphene copper-based brake are tested, and the test results are shown in Table 1. It can be seen from Table 1 that the tensile strength of the graphene copper-based brake pad is 846 MPa, the Vickers hardness is 247 HV, the wear amount is 0.0422 g, and the thermal conductivity is 463 W / (m·K), indicating that through the preparation process of powder mixing, cold isostatic pressing, vacuum sintering, solution heat treatment and aging heat treatment, under the condition of solution heat treatment with a heating temperature of 600 °C and a heat preservation time of 2 h, a graphene copper-based brake pad with high strength, high hardness, low wear amount and high thermal conductivity can also be prepared.

[0126] Example 8

[0127] This embodiment is basically the same as the preparation method of Embodiment 3, except that: when performing solution heat treatment on the cured blank in step (5), the heating temperature is 800 °C and the holding time is 2 h. Tensile strength, Vickers hardness, wear amount and thermal conductivity of this graphene copper-based brake are tested, and the test results are shown in Table 1. It can be seen from Table 1 that the tensile strength of the graphene copper-based brake pad is 841 MPa, the Vickers hardness is 243 HV, the wear amount is 0.0439 g, and the thermal conductivity is 462 W / (m·K). It shows that through the preparation process of powder mixing, cold isostatic pressing, vacuum sintering, solution heat treatment and aging heat treatment, under the solution heat treatment conditions of a heating temperature of 800 °C and a holding time of 2 h, it is also possible to prepare a graphene copper-based brake pad with high strength, high hardness, low wear amount and high thermal conductivity.

[0128] Example 9

[0129] This embodiment is basically the same as the preparation method of Embodiment 3, except that: when performing aging heat treatment on the cured blank after solution heat treatment in step (5), the heating temperature is 300 °C and the holding time is 2 h. Tensile strength, Vickers hardness, wear amount and thermal conductivity of this graphene copper-based brake are tested, and the test results are shown in Table 1. It can be seen from Table 1 that the tensile strength of the graphene copper-based brake pad is 886 MPa, the Vickers hardness is 269 HV, the wear amount is 0.0336 g, and the thermal conductivity is 478 W / (m·K). It shows that through the preparation process of powder mixing, cold isostatic pressing, vacuum sintering, solution heat treatment and aging heat treatment, under the aging heat treatment conditions of a heating temperature of 300 °C and a holding time of 2 h, it is also possible to prepare a graphene copper-based brake pad with high strength, high hardness, low wear amount and high thermal conductivity.

[0130] Example 10

[0131] This embodiment is basically the same as the preparation method of Embodiment 3, except that: when performing aging heat treatment on the cured blank after solution heat treatment in step (5), the heating temperature is 400 °C and the holding time is 4 h. Tensile strength, Vickers hardness, wear amount and thermal conductivity of this graphene copper-based brake are tested, and the test results are shown in Table 1. It can be seen from Table 1 that the tensile strength of the graphene copper-based brake pad is 893 MPa, the Vickers hardness is 274 HV, the wear amount is 0.0325 g, and the thermal conductivity is 479 W / (m·K). It shows that through the preparation process of powder mixing, cold isostatic pressing, vacuum sintering, solution heat treatment and aging heat treatment, under the aging heat treatment conditions of a heating temperature of 400 °C and a holding time of 4 h, it is also possible to prepare a graphene copper-based brake pad with high strength, high hardness, low wear amount and high thermal conductivity.

[0132] Comparative Example 1

[0133] This comparative example has basically the same preparation method as Example 1, except that: without adding graphene slurry, directly make copper-based powder into copper-based friction materials and copper-based brake pads. The specific steps are as follows:

[0134] (1) Provide copper-based powder:

[0135] The copper-based powder is made from raw materials with the following mass percentages: copper 84.75%, tin 6%, zinc 5%, iron 1.5%, nickel 2%, chromium 0.2%, lead 0.2%, phosphorus 0.2%, bismuth 0.1%, and silicon 0.05%; the particle size of the copper-based powder is 0.1 - 100 μm;

[0136] (2) Load the copper-based powder into a special silica gel elastic mold and seal it; then place the powder-loaded mold into a cold isostatic pressing cylinder body, and perform powder compaction molding through cold isostatic pressing. The maximum pressure is 150 MPa, and the pressure holding time is 60 min to obtain a green compact;

[0137] (3) Place the green compact into a vacuum sintering furnace for sintering. The sintering temperature is 900 °C, the sintering time is 2 h, and the vacuum degree is <0.01 Pa; after sintering, cool it to room temperature with the furnace to obtain a mature compact;

[0138] (4) Place the mature compact into a vacuum heat treatment furnace for solution heat treatment and aging heat treatment to obtain a graphene copper-based composite material; among them, the solution heat treatment includes the following steps: under a vacuum degree of ≤0.01 Pa, heat the above-mentioned mature compact to 700 °C, hold for 2 h, and cool it to room temperature with water; the aging heat treatment includes the following steps: under a vacuum degree of ≤0.01 Pa, heat the mature compact after solution heat treatment to 400 °C, hold for 2 h, and air-cool it to room temperature to obtain a copper-based friction material;

[0139] (5) First, perform surface treatment on the copper-based friction material with a sandblasting machine. The sandblasting air pressure is 0.6 MPa, the sandblasting time is 10 min, and the shot peening is Al2O3 ceramic; then use a grinding machine to polish its surface smoothly to obtain a copper-based brake pad.

[0140] (6) Performance testing of the copper-based brake pad:

[0141] Test the tensile strength, Vickers hardness, wear amount, and thermal conductivity of the copper-based brake. The test results are shown in Table 1. It can be seen from Table 1 that the tensile strength of the copper-based brake pad is 556 MPa, the Vickers hardness is 172 HV, the wear amount is 0.0608 g, and the thermal conductivity is 391 W / (M·K), indicating that without adding graphene to modify the copper-based powder, the strength, hardness, wear resistance, and thermal conductivity of the copper-based brake pad have all decreased.

[0142] Comparative Example 2

[0143] This comparative example is basically the same as the preparation method of Example 3, except that: solution heat treatment and aging heat treatment are not carried out after vacuum sintering. The specific steps are as follows:

[0144] (1) Provide graphene slurry and copper-based powder:

[0145] The graphene slurry is made of raw materials with the following mass percentages: 80% solvent, 15% graphene powder, and 5% dispersant; among them, ethanol is selected as the solvent, polyethylene glycol is selected as the dispersant, and the sheet diameter of the graphene powder is 0.1 - 5 μm; to improve the dispersibility of graphene, the above raw materials are mixed evenly by ultrasonic waves;

[0146] The copper-based powder is made of raw materials with the following mass percentages: 84.75% copper, 6% tin, 5% zinc, 1.5% iron, 2% nickel, 0.2% chromium, 0.2% lead, 0.2% phosphorus, 0.1% bismuth, and 0.05% silicon; the particle size of the copper-based powder is 0.1 - 100 μm;

[0147] The content of graphene powder in the graphene copper-based composite material is 1 wt.%.

[0148] (2) Put the graphene slurry and the copper-based powder into a powder mixer and mix evenly. The powder mixing time is 4 h, and the rotation speed is 200 rpm; then dry and encapsulate to obtain the powder;

[0149] (3) Load the powder into a special silicone elastic mold and seal it; then put the powder-loaded mold into a cold isostatic pressing cylinder body, and perform powder pressing and forming through cold isostatic pressing. The maximum pressure is 150 MPa, and the pressure holding time is 60 min to obtain a green blank;

[0150] (4) Put the green blank into a vacuum sintering furnace for sintering. The sintering temperature is 900 °C, the sintering time is 2 h, and the vacuum degree is <0.01 Pa; after sintering, cool it to room temperature with the furnace to obtain a cooked blank;

[0151] (5) First, perform surface treatment on the graphene copper-based composite material through a sandblasting machine. The sandblasting air pressure is 0.6 MPa, the sandblasting time is 10 min, and the shot peening is Al2O3 ceramic; then use a grinding machine to polish its surface smoothly to obtain a graphene copper-based brake pad.

[0152] (6) Performance test of the graphene copper-based brake pad:

[0153] The tensile strength, Vickers hardness, wear amount, and thermal conductivity of the graphene copper-based brake were tested, and the test results are shown in Table 1. It can be seen from Table 1 that the tensile strength of the graphene copper-based brake pad is 515 MPa, the Vickers hardness is 163 HV, the wear amount is 0.0723 g, and the thermal conductivity is 425 W / (m·K). Compared with Example 3, the strength, hardness, wear resistance, and thermal conductivity of this graphene copper-based brake pad are significantly reduced; compared with Example 1, the thermal conductivity of this graphene copper-based brake pad has increased, but the reduction amplitudes of its strength, hardness, and wear resistance are very obvious. This shows that on the basis of the powder mixing, cold isostatic pressing, and vacuum sintering processes, the introduction of solution heat treatment and aging heat treatment is not only beneficial to further improve the thermal conductivity of the graphene copper-based brake pad, but also can greatly improve the strength, hardness, and wear resistance of the brake pad.

[0154] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0155] The above-described embodiments merely represent several implementation manners of the present invention, and the description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims, and the description and drawings can be used to explain the content of the claims.

Claims

1. A preparation method of a graphene copper-based composite material, characterized in that, It includes the following steps: Mix graphene slurry and copper-based powder to obtain a powder body; Press the powder body into a shape to obtain a green body; Vacuum sinter the green body to obtain a sintered body; Perform solution heat treatment and aging heat treatment on the sintered body to obtain the graphene copper-based composite material; Among them, the chemical composition of the copper-based powder includes copper, tin, zinc, and one or more of iron, nickel, chromium, lead, phosphorus, bismuth, and silicon elements; the copper-based powder contains 75wt.% - 92wt.% of copper element, 5wt.% - 8wt.% of tin element, and 2wt.% - 8wt.% of zinc element; The content of graphene powder in the graphene copper-based composite material is 0.05wt.% - 2wt.%; The vacuum sintering includes the following steps: under a vacuum degree of ≤0.01 Pa, sinter the green body at 800°C - 1000°C for 0.5 - 4 h, and then cool it to room temperature; The solution heat treatment includes the following steps: under a vacuum degree of ≤0.01 Pa, heat the sintered blank at 600°C - 800°C for 0.5 - 4 h, and then cool it to room temperature.

2. The preparation method of the graphene copper-based composite material according to claim 1, characterized in that The solution heat treatment includes the following steps: under a vacuum degree of ≤0.01 Pa, heat the sintered blank at 700°C for 2 h, and then cool it to room temperature.

3. The preparation method of the graphene copper-based composite material according to claim 1, characterized in that, The aging heat treatment includes the following steps: under a vacuum degree of ≤0.01 Pa, heat the sintered blank after solution heat treatment at 200°C - 500°C for 0.5 - 4 h, and then cool it to room temperature.

4. The preparation method of the graphene copper-based composite material according to any one of claims 1 to 3, characterized in that, The vacuum sintering includes the following steps: under a vacuum degree of ≤0.01 Pa, sinter the green body at 900°C for 2 h, and then cool it to room temperature.

5. The preparation method of the graphene copper-based composite material according to claim 4, characterized in that, The method of pressing into a shape is one of cold isostatic pressing, hydraulic pressing, and die pressing.

6. The preparation method of the graphene copper-based composite material according to claim 5, characterized in that, The cold isostatic pressing satisfies one or more of the following conditions: 1) The maximum forming pressure is 100 MPa - 200 MPa; 2) The pressure holding time is 10 min - 120 min.

7. The preparation method of the graphene copper-based composite material according to claim 1, wherein, The graphene slurry includes a solvent, graphene powder, and a dispersant.

8. The preparation method of the graphene copper-based composite material according to claim 7, wherein, The graphene slurry satisfies one or more of the following conditions: 1) The sheet diameter of the graphene powder is 0.1 - 5 μm; 2) The solvent is water and / or ethanol; 3) The dispersant is one or more of polyethylene glycol, polyvinyl alcohol, and ammonium polyacrylate; 4) The mass ratio of the solvent, the graphene powder, and the dispersant is (75 - 95):(3 - 25):(0.5 - 5).

9. The preparation method of the graphene copper-based composite material according to claim 1, characterized in that, The particle size of the copper-based powder is 0.1 μm - 100 μm.

10. A graphene copper-based composite material, characterized in that, It is prepared by using the preparation method of the graphene copper-based composite material according to any one of claims 1 - 9.

11. A brake pad, characterized in that, It is prepared by performing surface treatment on the graphene copper-based composite material according to claim 10.

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