Graphene carbon nanotube copper-based electric sliding contact composite material and directional forming method

Abstract

The invention relates to the technical field of conductive materials, in particular to a graphene carbon nanotube copper-based electric sliding contact composite material and a directional forming method. The composite material is provided with a sliding surface and is characterized by comprising a metal matrix, the metal matrix is a copper matrix or a copper alloy matrix, graphene sheets and carbon nanotubes are uniformly dispersed in the metal matrix, and the carbon nanotubes are used for bridging adjacent graphene sheets; the included angle between the 002 crystal face orientation of at least 80% of the graphene sheets and the sliding surface of the composite material is smaller than 15 degrees. The composite material is used for a high-speed railway pantograph slide plate, a high-power motor brush or a power switch contact, and has the advantages of extremely low friction and wear, excellent arc ablation resistance, high mechanical strength and conductivity and long service life.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of conductive materials, and particularly relates to a graphene carbon nanotube copper-based electric sliding contact composite material and a directional forming method. BACKGROUND

[0002] In the fields of high-speed railway and high-power motor, electric sliding contact components (such as pantograph slide plate and contact net conductor, motor brush and commutator) are the key to ensure stable power transmission. These components bear the coupling effect of mechanical friction, electrical wear and arc ablation when working, and the working conditions are extremely harsh. The traditional copper-based composite materials (such as copper-graphite and copper-metal oxide) often face the following challenges: performance trade-off: increasing the content of graphite can improve the lubricity, but will seriously sacrifice the electrical conductivity and strength of the material. ① Anisotropy: in the traditional powder metallurgy prepared material, the orientation of the flaky graphite is random, which leads to the anisotropy of the friction and wear performance, and the advantage of low interlayer friction coefficient of the graphite cannot be fully utilized. ② Poor arc resistance: the arc generated when the current is turned off or the contact is poor can instantly produce high temperature, melt the surface of the material and form pits, accelerating the failure. ③ Insufficient wear resistance: under high-speed sliding, the traditional materials wear out quickly, have short service life and need to be replaced frequently, affecting the continuous operation of the equipment.

[0003] Graphene has extremely high in-plane strength, thermal conductivity and extremely low interlayer friction coefficient. If the basal plane (i.e. (002) crystal plane) of graphene is parallel to the sliding surface, the self-lubricating property of graphene can be maximally utilized. Carbon nanotubes have extremely high aspect ratio and toughness, which can effectively play the role of toughening, strengthening and inhibiting crack propagation. However, how to introduce both of them into the copper matrix and realize the directional arrangement of graphene is a technical problem that the prior art has not solved well. SUMMARY

[0004] The present application aims to provide a graphene carbon nanotube copper-based electric sliding contact composite material and a directional forming method. The composite material is used for high-speed railway pantograph slide plate, high-power motor brush or electric switch contact, has extremely low friction and wear, excellent arc ablation resistance, high mechanical strength and electrical conductivity, and long service life.

[0005] To achieve the above purpose, the present application adopts the following technical solutions: A graphene carbon nanotube copper-based electric sliding contact composite material, the composite material has a sliding surface, comprising a metal matrix, the metal matrix is a copper matrix or a copper alloy matrix, the metal matrix uniformly disperses graphene sheets and carbon nanotubes, and the carbon nanotubes are used to bridge adjacent graphene sheets. Further, in the composite material, the volume fraction of the graphene is 2%-10%, and the volume fraction of the carbon nanotubes is 0.5%-5%.

[0006] Furthermore, the graphene sheet has a diameter of 5-50 μm and the number of graphene layers is less than 10.

[0007] Furthermore, the carbon nanotubes are multi-walled carbon nanotubes, with a length of 1-20 μm and a diameter of 5-50 nm.

[0008] A method for directional molding of a graphene carbon nanotube copper-based electrosliding contact composite material, wherein the method is used to prepare the graphene carbon nanotube copper-based electrosliding contact composite material according to any one of claims 1-4; The orientation molding method includes the following steps: (1) Preparation of composite powder: Metal powder, graphene sheets and carbon nanotubes are uniformly mixed by wet ball milling or solution ultrasonic mixing to obtain composite powder; (2) Pre-pressing: The composite powder is loaded into a mold and pre-pressed in one direction to obtain a green body; (3) Hot pressing sintering: The green blank is hot pressed and sintered in a reducing atmosphere or an inert atmosphere, and the direction of the pressure applied during the hot pressing sintering process is consistent with the direction of the unidirectional cold pressing pressure in step S2. (4) Plastic deformation processing: The sintered billet is subjected to plastic deformation processing, wherein the processing method is rolling, extrusion or forging along the pressure direction perpendicular to step (2); (5) Slicing and finishing: Slice the material along the rheological direction parallel to the plastic deformation process in step (4). The surface of the resulting sheet material is the sliding surface. The sliding surface is then finished.

[0009] Furthermore, in step (4), the deformation amount of the sintered billet after plastic deformation processing is greater than or equal to 60%.

[0010] Furthermore, in step (3), the pressure for hot pressing and sintering the green blank is 30-80 MPa, the sintering temperature is 800-950°C, and the holding time is 1-3 hours.

[0011] An electric sliding contact component includes the above-mentioned graphene carbon nanotube copper-based electric sliding contact composite material, wherein the electric sliding contact component is a pantograph sliding plate of a high-speed railway, a brush of a high-power motor, or a power switch contact.

[0012] The technical solution provided by this invention may include the following beneficial effects: (1) Extremely low friction and wear: The oriented graphene basal surface in the composite material provides a continuous and stable solid lubricating film, which can reduce the friction coefficient to below 0.15 and reduce the wear rate by an order of magnitude compared with traditional copper-graphite materials.

[0013] (2) Excellent resistance to electric arc ablation: The high thermal conductivity of graphene and carbon nanotubes in the composite material allows the heat generated by the electric arc to be quickly dissipated, reducing local high temperature; at the same time, the introduction of the reinforcing phase increases the recrystallization temperature and high temperature strength of the material, effectively resisting the melting and erosion of the electric arc.

[0014] (3) High mechanical strength and conductivity: The copper or copper alloy metal matrix ensures excellent conductivity. The synergistic reinforcement of carbon nanotubes and graphene sheets compensates for the strength loss caused by the introduction of graphene, so that the material has high wear resistance while maintaining high conductivity.

[0015] (4) Long life and high reliability: The improvement of overall performance directly translates into a significant extension of the service life of components, which is particularly suitable for fields with extremely high requirements for reliability and life, such as high-speed railways and high-power motors. Detailed Implementation

[0016] An embodiment of the present invention provides a graphene-carbon nanotube copper-based electrosliding contact composite material, the composite material having a sliding surface, including a metal matrix, the metal matrix being a copper matrix or a copper alloy matrix, wherein graphene sheets and carbon nanotubes are uniformly dispersed within the metal matrix, and the carbon nanotubes are used to bridge adjacent graphene sheets. At least 80% of the graphene sheets have an 002 crystal plane orientation with an angle of less than 15° between it and the sliding surface of the composite material.

[0017] In this scheme, carbon nanotubes are randomly distributed within the metal matrix, forming a three-dimensional network. Like "steel bars," they strengthen the matrix, preventing the graphene sheets from being pulled out under pressure; furthermore, their high thermal conductivity facilitates rapid heat dissipation, enhancing resistance to arc ablation. They bridge the oriented graphene sheets, forming a synergistically reinforced composite system, resulting in an electrical contact material with excellent overall performance. The vast majority (≥80%) of the graphene sheets in the metal matrix have (002) crystal planes parallel to the sliding surface (angle less than 15°). This ensures that during sliding, friction primarily occurs between the low-friction coefficient basal planes of the graphene, significantly reducing frictional wear.

[0018] Preferably, in the composite material, the volume fraction of graphene is 2%-10%, and the volume fraction of carbon nanotubes is 0.5%-5%.

[0019] More preferably, the graphene sheet has a diameter of 5-50 μm and the number of graphene layers is less than 10.

[0020] More preferably, the carbon nanotube is a multi-walled carbon nanotube, and the length of the carbon nanotube is 1-20 μm and the diameter is 5-50 nm.

[0021] Accordingly, the present invention also provides a method for directional molding of a graphene-carbon nanotube copper-based electrosliding contact composite material, used to prepare the above-mentioned composite material; the directional molding method includes the following steps: (1) Preparation of composite powder: Metal powder, graphene sheets and carbon nanotubes are uniformly mixed by wet ball milling or solution ultrasonic mixing to obtain composite powder; (2) Pre-pressing: The composite powder is loaded into a mold and pre-pressed in one direction to obtain a green body; (3) Hot pressing sintering: The green blank is hot pressed and sintered in a reducing atmosphere or an inert atmosphere, and the direction of the pressure applied during the hot pressing sintering process is consistent with the direction of the unidirectional cold pressing pressure in step S2. (4) Plastic deformation processing: The sintered billet is subjected to plastic deformation processing, wherein the processing method is rolling, extrusion or forging along the pressure direction perpendicular to step (2); (5) Slicing and finishing: Slice the material along the rheological direction parallel to the plastic deformation process in step (4). The surface of the resulting sheet material is the sliding surface. The sliding surface is then finished.

[0022] This invention utilizes a unique "pressure-induced rheological orientation" process to achieve the directional alignment of graphene in a copper matrix, synergistically enhancing the performance of carbon nanotubes to obtain an electrical contact material with excellent overall properties. Specifically, unidirectional cold pressing and unidirectional hot pressing initially induce the graphene sheets to align perpendicular to the pressure direction (at this point, their basal planes are parallel to the upper and lower surfaces of the compact). Large-deformation rolling or extrusion of the sintered compact forces the internal sheet-like reinforcing phases to reorient along the rheological direction during plastic rheological changes in the metal matrix. After this step, the graphene sheets tend to align parallel to the rolling plane or extrusion direction. Slicing along a direction parallel to the material's rheological direction yields a final product with a sliding surface nearly parallel to the graphene basal plane.

[0023] Preferably, in step (4), the deformation amount of the sintered billet after plastic deformation processing is greater than or equal to 60%.

[0024] Preferably, in step (3), the pressure for hot pressing and sintering the green blank is 30-80 MPa, the sintering temperature is 800-950°C, and the holding time is 1-3 hours.

[0025] Accordingly, the present invention also provides an electric sliding contact component, comprising the above-mentioned graphene carbon nanotube copper-based electric sliding contact composite material, wherein the electric sliding contact component is a high-speed railway pantograph sliding plate, a high-power motor brush, or a power switch contact.

[0026] The present invention will be further illustrated below through examples and comparative examples.

[0027] Embodiments 1-5 of the present invention Example 1: Directional forming method of graphene-carbon nanotube copper-based electrosliding contact composite material Raw materials: electrolytic copper powder (average particle size 50μm), few-layer graphene (sheet diameter 10-20μm, number of layers 3-5), multi-walled carbon nanotubes (length 5-15μm, diameter 10-20nm).

[0028] The orientation molding method in this embodiment includes the following steps: (1) Preparation of composite powder: Copper powder (92%), graphene (6%) and carbon nanotubes (2%) were placed in an alcohol solvent by volume fraction and ball-milled for 4 hours at 200 rpm using a planetary ball mill with a ball-to-powder ratio of 5:1. Then the powder was dried in a vacuum drying oven at 80℃.

[0029] (2) Pre-pressing: The composite powder is loaded into a cylindrical mold and unidirectionally cold-pressed at a pressure of 400MPa to obtain a green blank with a diameter of 50mm.

[0030] (3) Hot pressing sintering: The green blank is placed in a graphite mold and then placed in a hot pressing sintering furnace. Under vacuum, the temperature is raised to 900°C at 15°C / min, and then an axial pressure of 50MPa is applied. The temperature and pressure are maintained for 2 hours, and then the furnace is cooled.

[0031] (4) Plastic deformation processing: The sintered cylindrical billet is rolled in multiple passes at room temperature, with a total reduction of 80% (i.e., the thickness is reduced by 80%), to obtain sheet and strip. During this process, the material extends along the rolling direction.

[0032] (5) Slicing and finishing: Cut out test samples along the direction parallel to the rolling surface (i.e. the surface of the strip). Polish the sliding surface to obtain the final product.

[0033] Example 2: Directional forming method of graphene-carbon nanotube copper-based electrosliding contact composite material Raw materials: electrolytic copper powder (average particle size 50μm), few-layer graphene (sheet diameter 5-10μm, number of layers 3-5), multi-walled carbon nanotubes (length 1-10μm, diameter 5-10nm).

[0034] The orientation molding method in this embodiment includes the following steps: (1) Preparation of composite powder: Copper powder (85%), graphene (10%) and carbon nanotubes (5%) were placed in an alcohol solvent by volume fraction and ball-milled for 4 hours at 200 rpm using a planetary ball mill with a ball-to-powder ratio of 5:1. Then, the powder was dried in a vacuum drying oven at 80℃.

[0035] (2) Pre-pressing: The composite powder is loaded into a cylindrical mold and unidirectionally cold-pressed at a pressure of 400MPa to obtain a green blank with a diameter of 50mm.

[0036] (3) Hot pressing sintering: The green blank is placed in a graphite mold and then placed in a hot pressing sintering furnace. Under vacuum, the temperature is raised to 900°C at 15°C / min, and then an axial pressure of 50MPa is applied. The temperature and pressure are maintained for 2 hours, and then the furnace is cooled.

[0037] (4) Plastic deformation processing: The sintered cylindrical billet is rolled in multiple passes at room temperature, with a total reduction of 80% (i.e., the thickness is reduced by 80%), to obtain sheet and strip. During this process, the material extends along the rolling direction.

[0038] (5) Slicing and finishing: Cut out test samples along the direction parallel to the rolling surface (i.e. the surface of the strip). Polish the sliding surface to obtain the final product.

[0039] Example 3: Directional forming method of graphene-carbon nanotube copper-based electrosliding contact composite material Raw materials: electrolytic copper powder (average particle size 50μm), few-layer graphene (sheet diameter 30-50μm, number of layers 6-9), multi-walled carbon nanotubes (length 10-20μm, diameter 25-50nm).

[0040] The orientation molding method in this embodiment includes the following steps: (1) Preparation of composite powder: Copper powder (85%), graphene (10%) and carbon nanotubes (5%) were placed in an alcohol solvent by volume fraction and ball-milled for 4 hours at 200 rpm using a planetary ball mill with a ball-to-powder ratio of 5:1. Then, the powder was dried in a vacuum drying oven at 80℃.

[0041] (2) Pre-pressing: The composite powder is loaded into a cylindrical mold and unidirectionally cold-pressed at a pressure of 400MPa to obtain a green blank with a diameter of 50mm.

[0042] (3) Hot pressing sintering: The green blank is placed in a graphite mold and then placed in a hot pressing sintering furnace. Under vacuum, the temperature is raised to 900°C at 15°C / min, and then an axial pressure of 50MPa is applied. The temperature and pressure are maintained for 2 hours, and then the furnace is cooled.

[0043] (4) Plastic deformation processing: The sintered cylindrical billet is rolled in multiple passes at room temperature, with a total reduction of 80% (i.e., the thickness is reduced by 80%), to obtain sheet and strip. During this process, the material extends along the rolling direction.

[0044] (5) Slicing and finishing: Cut out test samples along the direction parallel to the rolling surface (i.e. the surface of the strip). Polish the sliding surface to obtain the final product.

[0045] Example 4: Directional forming method of graphene-carbon nanotube copper-based electrosliding contact composite material Raw materials: electrolytic copper powder (average particle size 50μm), few-layer graphene (sheet diameter 10-20μm, number of layers 3-5), multi-walled carbon nanotubes (length 5-15μm, diameter 10-20nm).

[0046] The orientation molding method in this embodiment includes the following steps: (1) Preparation of composite powder: Copper powder (97.5%), graphene (2%) and carbon nanotubes (0.5%) were placed in an alcohol solvent by volume fraction and ball-milled for 4 hours at 200 rpm using a planetary ball mill with a ball-to-powder ratio of 5:1. Then, they were dried in a vacuum drying oven at 80℃.

[0047] (2) Pre-pressing: The composite powder is loaded into a cylindrical mold and unidirectionally cold-pressed at a pressure of 400MPa to obtain a green blank with a diameter of 50mm.

[0048] (3) Hot pressing sintering: The green blank is placed in a graphite mold and then placed in a hot pressing sintering furnace. Under vacuum, the temperature is raised to 800°C at 15°C / min, and then an axial pressure of 80MPa is applied. The temperature and pressure are maintained for 3 hours, and then the furnace is cooled.

[0049] (4) Plastic deformation processing: The sintered cylindrical billet is rolled in multiple passes at room temperature, with a total reduction of 80% (i.e., the thickness is reduced by 80%), to obtain sheet and strip. During this process, the material extends along the rolling direction.

[0050] (5) Slicing and finishing: Cut out test samples along the direction parallel to the rolling surface (i.e. the surface of the strip). Polish the sliding surface to obtain the final product.

[0051] Example 5: Directional forming method of graphene-carbon nanotube copper-based electrosliding contact composite material Raw materials: electrolytic copper powder (average particle size 50μm), few-layer graphene (sheet diameter 30-50μm, number of layers 6-9), multi-walled carbon nanotubes (length 10-20μm, diameter 25-50nm).

[0052] The orientation molding method in this embodiment includes the following steps: (1) Preparation of composite powder: Copper powder (91%), graphene (8%) and carbon nanotubes (1%) were placed in an alcohol solvent by volume fraction and ball-milled for 4 hours at 200 rpm using a planetary ball mill with a ball-to-powder ratio of 5:1. Then the powder was dried in a vacuum drying oven at 80℃.

[0053] (2) Pre-pressing: The composite powder is loaded into a cylindrical mold and unidirectionally cold-pressed at a pressure of 400MPa to obtain a green blank with a diameter of 50mm.

[0054] (3) Hot pressing sintering: The green blank is placed in a graphite mold and then placed in a hot pressing sintering furnace. Under vacuum, the temperature is increased to 950°C at 15°C / min, and then an axial pressure of 30MPa is applied. The temperature and pressure are maintained for 1 hour, and then the furnace is cooled.

[0055] (4) Plastic deformation processing: The sintered cylindrical billet is rolled in multiple passes at room temperature, with a total reduction of 80% (i.e., the thickness is reduced by 80%), to obtain sheet and strip. During this process, the material extends along the rolling direction.

[0056] (5) Slicing and finishing: Cut out test samples along the direction parallel to the rolling surface (i.e. the surface of the strip). Polish the sliding surface to obtain the final product.

[0057] Comparative Example 1 Using the same component ratio, but omitting step (4) (plastic deformation processing), that is, directly slicing and refining the hot-pressed sintered blank, the resulting composite material has random orientation of the graphene sheets inside.

[0058] The composite materials of the examples and comparative examples were subjected to performance tests and characterization, as detailed below: 1. Microstructure characterization: X-ray diffraction (XRD) texture analysis was performed on the cross-sections of the samples from Examples 1-5 of this invention. The results showed that the intensity of the (002) diffraction peak was significantly higher in the direction parallel to the sliding surface than in the vertical direction. It was calculated that approximately 85% of the graphene sheets had an angle of less than 15° with the sliding surface. Scanning electron microscopy (SEM) revealed that carbon nanotubes were uniformly distributed around the copper grain boundaries and the graphene.

[0059] 2. Friction and Wear Test: The test was conducted on a ring-block friction and wear testing machine. The mating parts were chromium-zirconium copper rings, the load was 50 N, and the sliding speed was 10 m / s. The test results showed that the stable friction coefficient of Examples 1-5 of this invention was 0.10-0.15, and the wear rate was only (1.3-1.8) × 10⁻ 6 1) The friction coefficient of the comparative example fluctuated between 0.20 and 0.28, and the wear rate was 8.0 × 10⁻ mm³ / N·m; 2) 6 mm³ / N·m.

[0060] 3. Arc Erosion Resistance Test: An arc erosion testing machine was used. Under conditions of 100A current and 220V voltage, the energizer was applied for 0.1s at a time, with a 1s interval, for a total of 1000 cycles. The test results were as follows: The ablation areas in Examples 1-5 of this invention were smooth with only slight discoloration, and the ablation weight loss was 7-10mg. The ablation areas in the comparative examples showed obvious melting pits and spatter, with an ablation weight loss of 35mg.

[0061] 4. Electrical conductivity measurement: The electrical conductivity of the composite materials in Examples 1-5 of this invention reaches 75% IACS (International Standard for Annealed Copper), which is much higher than that of traditional powder metallurgy copper-graphite materials (usually <50% IACS).

[0062] Other components and operations of the graphene carbon nanotube copper-based electrosliding contact composite material and the directional molding method according to embodiments of the present invention are known to those skilled in the art and will not be described in detail here.

[0063] In the description of this specification, references to terms such as "embodiment," "example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0064] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A graphene-carbon nanotube copper-based electrosliding contact composite material, wherein the composite material has a sliding surface, characterized in that, It includes a metal matrix, wherein the metal matrix is ​​a copper matrix or a copper alloy matrix, and graphene sheets and carbon nanotubes are uniformly dispersed in the metal matrix, wherein the carbon nanotubes are used to bridge adjacent graphene sheets. At least 80% of the graphene sheets have an 002 crystal plane orientation with an angle of less than 15° between it and the sliding surface of the composite material.

2. The composite material according to claim 1, characterized in that, In the composite material, the volume fraction of graphene is 2%-10%, and the volume fraction of carbon nanotubes is 0.5%-5%.

3. The composite material according to claim 1, characterized in that, The graphene sheet has a diameter of 5-50 μm and has fewer than 10 layers.

4. The composite material according to claim 1, characterized in that, The carbon nanotubes are multi-walled carbon nanotubes, with a length of 1-20 μm and a diameter of 5-50 nm.

5. A method for directional molding of a graphene-carbon nanotube copper-based electrosliding contact composite material, characterized in that, The orientation molding method is used to prepare the graphene carbon nanotube copper-based electrosliding contact composite material according to any one of claims 1-4; The orientation molding method includes the following steps: (1) Preparation of composite powder: Metal powder, graphene sheets and carbon nanotubes are uniformly mixed by wet ball milling or solution ultrasonic mixing to obtain composite powder; (2) Pre-pressing: The composite powder is loaded into a mold and pre-pressed in one direction to obtain a green body; (3) Hot pressing sintering: The green blank is hot pressed and sintered in a reducing atmosphere or an inert atmosphere, and the direction of the pressure applied during the hot pressing sintering process is consistent with the direction of the unidirectional cold pressing pressure in step S2. (4) Plastic deformation processing: The sintered billet is subjected to plastic deformation processing, wherein the processing method is rolling, extrusion or forging along the pressure direction perpendicular to step (2); (5) Slicing and finishing: Slice the material along the rheological direction parallel to the plastic deformation process in step (4). The surface of the resulting sheet material is the sliding surface. The sliding surface is then finished.

6. The orientation molding method according to claim 5, characterized in that, In step (4), the deformation amount of the sintered billet after plastic deformation processing is greater than or equal to 60%.

7. The orientation molding method according to claim 5, characterized in that, In step (3), the pressure for hot pressing and sintering the green blank is 30-80 MPa, the sintering temperature is 800-950°C, and the holding time is 1-3 hours.

8. An electrically sliding contact component, characterized in that, The invention includes the graphene carbon nanotube copper-based electro-sliding contact composite material according to any one of claims 1-4, wherein the electro-sliding contact component is a high-speed railway pantograph sliding plate, a high-power motor brush, or a power switch contact.