Graphene / copper-based self-lubricating composite material and preparation method thereof

Abstract

The invention belongs to the field of metal-based composite materials, and discloses a graphene / copper-based self-lubricating composite material and a preparation method thereof. According to the preparation method, a synergistic process combining laser scanning shaping treatment and die casting is adopted, a micro-metallurgical bonding point is established between graphene and copper powder in advance before die casting through laser scanning, the interface bonding force is remarkably enhanced, early falling of a lubricating phase in the friction process is avoided, and the service life is prolonged; the problems of interface bonding and dispersion stability of graphene are solved; through die casting, the near-net forming problem of complex parts is efficiently solved, so that the pre-composite powder can effectively resist melt scouring in the die casting process, and graphene is prevented from being reagglomerated; the obtained composite material has excellent self-lubricating property, high strength and good conductivity. The friction coefficient of the obtained composite material is 0.10-0.28, the tensile strength is 300 MPa or above, the electric conductivity is not lower than 85% IACS, and the composite material can be widely applied to the fields of mechanical equipment, aerospace, precision parts and the like.

Description

Technical Field

[0001] This invention belongs to the field of metal matrix composite technology, and particularly relates to a graphene / copper matrix composite material with self-lubricating properties and its preparation method. Background Technology

[0002] Copper is widely used in key components such as bearings, sliders, and electrical contacts in machinery, electronics, and transportation due to its excellent electrical and thermal conductivity and machinability. However, pure copper has low hardness and poor wear resistance, especially under dry friction or boundary lubrication conditions, making it prone to adhesive wear and leading to component failure.

[0003] To improve the wear resistance of copper, self-lubricating composite materials are typically prepared by adding solid lubricants (such as graphite and molybdenum disulfide). However, the interfacial bonding between traditional solid lubricating phases (such as graphite powder) and the copper matrix is ​​weak, and they are prone to peeling off during friction, resulting in limited lubrication life. Furthermore, adding large amounts of lubricating phase can significantly reduce the material's strength and conductivity.

[0004] Graphene, as a two-dimensional nanomaterial, possesses extremely high strength, excellent lubrication properties (extremely low coefficient of friction), and good thermal and electrical conductivity, making it an ideal reinforcing and lubricating phase. However, uniformly dispersing graphene into a copper matrix and achieving a strong interfacial bond remains a technical challenge. Common powder metallurgy methods (such as ball milling and hot pressing sintering) easily damage the graphene structure and are cumbersome, making it difficult to achieve near-net-shape forming of complex parts.

[0005] Die casting, as a near-net-shape forming process, boasts high production efficiency and is suitable for large-scale production of complex-shaped parts. However, traditional die casting is mainly applicable to low-melting-point alloys such as aluminum and zinc alloys. For copper alloys (with melting points as high as 1083℃), mold life and process control pose significant challenges. More importantly, whether in powder metallurgy or simple mechanical mixing die casting, the interaction between graphene and the copper matrix is ​​primarily physical adsorption or weak mechanical bonding. Interfacial adhesion remains a technical bottleneck, limiting further improvements in material properties.

[0006] Therefore, it is crucial to develop a novel preparation method that can achieve strong interfacial bonding between graphene and copper substrate. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a method for preparing a graphene / copper-based self-lubricating composite material with excellent self-lubricating properties, high strength and good electrical and thermal conductivity.

[0008] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows: A method for preparing a graphene / copper-based self-lubricating composite material includes the following steps: (1) Pre-treat the copper powder by heating it under vacuum or inert atmosphere; (2) The pretreated copper powder and the few-layer graphene powder are dry mixed so that the graphene is uniformly attached to the surface of the copper powder to obtain a mixed powder. (3) Spread the mixed powder on the substrate to form a powder layer, and then use a laser beam to scan and shape the powder layer under the protection of an inert atmosphere. After crushing and sieving, a pre-composite powder is obtained. (4) The pre-composite powder and molten copper liquid are injected together into the mold cavity at high speed, and the die casting is obtained after holding the pressure and cooling. (5) The die casting is subjected to stress-relief annealing and cooled to obtain the final product.

[0009] In the preparation method of the above-mentioned graphene / copper-based self-lubricating composite material, further, in step (1), the particle size of the copper powder is 15-75 μm, and the number of layers of the few-layer graphene powder is 3-10 layers with a specific surface area of ​​100-500 m². 2 / g.

[0010] Furthermore, in step (1), the pretreatment conditions are as follows: heat treatment at 200-400℃ for 1-2 hours.

[0011] Furthermore, in step (2), the volume ratio of copper powder to few-layer graphene powder is 95-99:1-5.

[0012] Furthermore, in step (3), the thickness of the powder layer is 50-200 μm.

[0013] Furthermore, in step (3), the conditions for the scanning and shaping process are as follows: the laser power is 100-500W, the scanning speed is 100-1000mm / s, the spot diameter is 50-200μm, and the powder layer is scanned with a checkerboard path with a line spacing of 60-100μm.

[0014] Furthermore, in step (4), the mass ratio of the pre-composite powder to the molten copper liquid is 1:50-100.

[0015] Furthermore, in step (4), the temperature of the molten copper liquid is 1100-1200℃, the preheating temperature of the mold cavity is 200-350℃, and the injection pressure of the high-speed injection is 50-150 MPa.

[0016] Furthermore, in step (5), the stress annealing conditions are as follows: stress annealing is performed at 400-550℃ for 1-3 hours.

[0017] Based on a general inventive concept, the present invention also provides a graphene / copper-based self-lubricating composite material obtained by the above preparation method, wherein the graphene / copper-based self-lubricating composite material has a friction coefficient of 0.10-0.28, a tensile strength of 300 MPa or more, and a conductivity of not less than 85% IACS.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The preparation method of the present invention adopts a synergistic process of laser scanning shaping treatment and die casting. Before die casting, laser scanning establishes micro-metallurgical bonding points between graphene and copper powder, which significantly enhances the interfacial bonding force, avoids the early shedding of the lubricating phase during the friction process, extends the service life, and solves the problem of interfacial bonding and dispersion stability of graphene. Meanwhile, die casting efficiently solves the problem of near-net-shape forming of complex parts, enabling the pre-composite powder to effectively resist melt erosion during the die casting process and prevent graphene from re-agglomerating. The resulting composite material has excellent self-lubricating properties, high strength, and good conductivity.

[0019] (2) The preparation method of the present invention, due to the uniform dispersion and strong interfacial bonding of graphene, only a very low amount of graphene needs to be added to make the composite material have both low friction coefficient and high strength, while maintaining the good electrical and thermal conductivity of the copper matrix, thus reducing the preparation cost; the laser scanning shaping step only causes slight sintering of the powder, which can avoid damage to the graphene structure; during the die casting process, the pre-composite powder can be uniformly dispersed in the molten copper liquid, reducing agglomeration, while reducing the wear of the mold on the copper alloy die casting, thus taking into account both production efficiency and product quality.

[0020] (3) The composite material prepared by the present invention has a friction coefficient of 0.10-0.28, a tensile strength of more than 300 MPa, and a conductivity of not less than 85% IACS. It can be widely used in mechanical equipment, aerospace, precision components and other fields. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This refers to the graphene / copper-based precomposite powder of Example 1 of the present invention.

[0023] Figure 2 This refers to the graphene / copper-based self-lubricating composite bulk material of Example 1 of the present invention. Detailed Implementation

[0024] A method for preparing a graphene / copper-based self-lubricating composite material includes the following steps: (1) Raw material preparation and pretreatment: Prepare copper powder with a particle size of 15-75μm and 3-10 layers with a specific surface area of ​​100-500m². 2 / g of few-layer graphene powder; the copper powder is pretreated by keeping it at 200-400℃ for 1-2h under vacuum or inert atmosphere; (2) Powder mixing: The pretreated copper powder and graphene are mixed at a ratio of 1.0%-5.0% by volume of graphene, and the mixture is dry-mixed using a colloid mill to ensure that the graphene is uniformly attached to the surface of the copper powder; preferably, the volume fraction of the graphene is 1.5%-3.0%; (3) Laser selective scanning and shaping: The uniformly mixed powder is spread on the substrate to form a powder layer with a thickness of 50-200μm; under the protection of an inert atmosphere, a laser beam is used to scan the powder layer along a preset path, with a laser power of 100-500W, a scanning speed of 100-1000mm / s, and a spot diameter of 50-200μm; the laser scanning causes the powder layer to undergo slight sintering to form a brittle sheet-like precomposite, but does not achieve complete densification; the obtained precomposite is slightly broken and sieved to obtain a precomposite powder with good flowability; preferably, the laser power is 250-350W and the scanning speed is 400-600mm / s; (4) Die casting: The pre-composite powder and molten copper liquid at a temperature of 1100-1200℃ are injected at high speed into the mold cavity preheated to 200-350℃ at a mass ratio of 1:50-100. The injection pressure is 50-150 MPa. The pressure is held until cooling to obtain the die casting. (5) Post-treatment: The die casting is subjected to stress-relief annealing at 400-550℃ for 1-3 hours and then cooled in the furnace.

[0025] The graphene / copper-based self-lubricating composite material prepared by the above method exhibits a strong chemical-mechanical composite interface formed between graphene and the copper matrix through laser-induced micrometallurgical action, with uniform dispersion. This composite material has a coefficient of friction of 0.10-0.28, a tensile strength of over 300 MPa, and a conductivity of not less than 85% IACS.

[0026] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0027] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0028] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0029] Example 1: A method for preparing a graphene / copper-based self-lubricating composite material according to the present invention includes the following steps: (1) Raw material preparation and pretreatment: Prepare 1 kg of brass powder with an average particle size of 45 μm, 3-5 layers, and a specific surface area of ​​300 m². 2 / g of few-layer graphene powder; brass powder was heat-treated at 300℃ for 1.5h under argon protection; (2) Powder mixing: The pretreated brass powder and graphene are mixed at a ratio of 2.0% by volume of graphene. The mixture is then dry-mixed for 4 hours at a speed of 40 rpm using a colloid mill to ensure that the graphene is uniformly attached to the surface of the copper powder, thus obtaining the mixed powder. (3) Laser selective scanning and shaping: The uniformly mixed powder is spread on the substrate to form a 100μm thick powder layer; in a high-purity argon protective chamber, a laser beam is used to scan the powder layer in a checkerboard path with a line spacing of 80μm to perform scanning and shaping treatment. The laser power is 300W, the scanning speed is 500mm / s, and the spot diameter is 100μm to obtain a slightly sintered sheet-like pre-composite. It is then gently ground and passed through a 100-mesh sieve to obtain a pre-composite powder with good flowability. Figure 1 ); (4) Die casting: Add the pre-composite powder into the cold chamber die casting machine, set the injection pressure to 80MPa, preheat the mold to 280℃, and then press the pre-composite powder and the molten copper liquid preheated to 1120℃ into the mold cavity at a mass ratio of 1:100. Hold the pressure until cooling to obtain the die casting. (5) Post-treatment: The die-cast parts were stress-relief annealed at 500℃ for 2 hours and then cooled in the furnace to obtain graphene / copper-based self-lubricating composite material (sample 1). Figure 2 ).

[0030] Tests showed that the composite material (sample 1) had an average friction coefficient as low as 0.18, a tensile strength as high as 320 MPa, and an electrical conductivity of 87% IACS.

[0031] Example 2: A method for preparing a graphene / copper-based self-lubricating composite material according to the present invention, the steps are the same as in Example 1, the only difference being that the volume fraction of graphene is 1.0% (sample 2), 3.0% (sample 3), and 5.0% (sample 4).

[0032] The composite material (sample 2) was tested and found to have an average friction coefficient of 0.23, a tensile strength of 305 MPa, and a conductivity of 91% IACS.

[0033] The composite material (sample 3) has an average friction coefficient of 0.15, a tensile strength of 330 MPa, and a conductivity of 85% IACS.

[0034] The composite material (sample 4) has an average friction coefficient of 0.13, a tensile strength of 310 MPa, and an electrical conductivity of 86% IACS.

[0035] Example 3: A method for preparing a graphene / copper-based self-lubricating composite material according to the present invention, the steps are the same as in Example 1, the only difference being that the average particle size of the brass powder is 15 μm (sample 5) and 75 μm (sample 6).

[0036] The composite material (sample 5) was tested and found to have an average friction coefficient of 0.16, a tensile strength of 345 MPa, and a conductivity of 85% IACS.

[0037] The composite material (sample 6) has an average friction coefficient of 0.21, a tensile strength of 300 MPa, and an electrical conductivity of 89% IACS.

[0038] Example 4: A method for preparing a graphene / copper-based self-lubricating composite material according to the present invention, the steps are the same as in Example 1, the only difference being that the specific surface area of ​​the few-layer graphene powder is 100 m². 2 / g (sample 7), 500m 2 / g (sample 8).

[0039] The composite material (sample 7) was tested and found to have an average friction coefficient of 0.22, a tensile strength of 310 MPa, and a conductivity of 88% IACS.

[0040] The composite material (sample 8) has an average friction coefficient of 0.14, a tensile strength of 325 MPa, and an electrical conductivity of 86% IACS.

[0041] Example 5: A method for preparing a graphene / copper-based self-lubricating composite material according to the present invention, the steps are the same as in Example 1, the only difference being the scanning and shaping conditions as follows: the laser power is 100W, the scanning speed is 300mm / s, the spot diameter is 50μm, and the powder layer is scanned using a checkerboard path with a line spacing of 80μm (sample 9); the laser power is 500W, the scanning speed is 800mm / s, the spot diameter is 200μm, and the powder layer is scanned using a checkerboard path with a line spacing of 80μm (sample 10).

[0042] The composite material (sample 9) was tested and found to have an average friction coefficient of 0.19, a tensile strength of 315 MPa, and a conductivity of 86% IACS.

[0043] The composite material (sample 10) has an average friction coefficient of 0.24, a tensile strength of 300 MPa, and an electrical conductivity of 88% IACS.

[0044] Example 6: A method for preparing a graphene / copper-based self-lubricating composite material according to the present invention, the steps are the same as in Example 1, the only difference being that the injection pressure is 50 MPa (sample 11) and 150 MPa (sample 12).

[0045] The composite material (sample 11) was tested and found to have an average friction coefficient of 0.25, a tensile strength of 300 MPa, and an electrical conductivity of 85% IACS.

[0046] The composite material (sample 12) has an average friction coefficient of 0.17, a tensile strength of 350 MPa, and an electrical conductivity of 89% IACS.

[0047] Example 7: A method for preparing a graphene / copper-based self-lubricating composite material according to the present invention, the steps are the same as in Example 1, the only difference being that stress-relief annealing is performed at 400°C for 2 hours (sample 13) and stress-relief annealing is performed at 550°C for 2 hours (sample 14).

[0048] The composite material (sample 13) was tested and found to have an average coefficient of friction of 0.20, a tensile strength of 325 MPa, and a conductivity of 84% IACS.

[0049] The composite material (sample 14) has an average friction coefficient of 0.17, a tensile strength of 300 MPa, and an electrical conductivity of 90% IACS.

[0050] Comparative Example 1: A method for preparing a graphene / copper-based self-lubricating composite material, the steps are the same as those for sample 1 in Example 1, the only difference being that the laser selective scanning shaping process in step (3) is not performed.

[0051] The composite material was tested and found to have an average coefficient of friction of 0.22, a tensile strength of 270 MPa, and an electrical conductivity of 78% IACS.

[0052] Comparative Example 2: A method for preparing a graphene / copper-based self-lubricating composite material, the steps are the same as those for sample 2 in Example 2, the only difference being that the laser selective scanning shaping process in step (3) is not performed.

[0053] The resulting composite material has an average friction coefficient of 0.28, a tensile strength of 265 MPa, and an electrical conductivity of 70% IACS.

[0054] Compared with Comparative Examples 1-2 which did not undergo laser selective scanning shaping, Examples 1-2, after undergoing laser selective scanning shaping, pre-established micro-metallurgical bonding points between graphene and copper powder before die casting, significantly enhancing the interfacial bonding force, avoiding early shedding of the lubricating phase during the friction process, and improving the overall performance of the material.

[0055] Comparative Example 3: A method for preparing a graphene / copper-based self-lubricating composite material using traditional powder metallurgy: Copper powder and graphene in the same proportion as in Example 1 were mixed by high-energy ball milling for 12 hours, then pressed into shape at 600 MPa, and finally sintered at 950°C in a hydrogen atmosphere for 2 hours.

[0056] The obtained material has severe damage to the graphene structure, resulting in agglomeration. The coefficient of friction is 0.35, the tensile strength is 190 MPa, and the conductivity is 66% IACS, which are far lower than those in Example 1 of this invention.

[0057] Compared with the traditional powder metallurgy method in Comparative Example 3, the graphene / copper-based self-lubricating composite material prepared by the present invention through a synergistic process combining laser selective scanning shaping and die casting exhibits significantly better friction reduction performance, mechanical properties, and process efficiency than the traditional method.

[0058] In summary, this invention first mixes copper powder with graphene, then uses selective laser scanning irradiation to strengthen the interface between graphene and copper, obtaining a pre-composite powder, which is finally die-cast. This invention solves the problems of graphene's easy agglomeration and weak interfacial bonding, resulting in a material with excellent self-lubricating properties, high strength, and good electrical conductivity. The prepared composite material can be widely used in mechanical equipment, aerospace, precision components, and other fields.

Claims

1. A method for preparing a graphene / copper-based self-lubricating composite material, characterized in that, Includes the following steps: (1) Pre-treat the copper powder by heating it under vacuum or inert atmosphere; (2) The pretreated copper powder and the few-layer graphene powder are dry mixed so that the graphene is uniformly attached to the surface of the copper powder to obtain a mixed powder. (3) Spread the mixed powder on the substrate to form a powder layer, and then use a laser beam to scan and shape the powder layer under the protection of an inert atmosphere. After crushing and sieving, a pre-composite powder is obtained. (4) The pre-composite powder and molten copper liquid are injected together into the mold cavity at high speed, and the pressure is maintained until cooling to obtain the die casting; (5) The die-cast part is subjected to stress-relief annealing and cooled to obtain the graphene / copper-based self-lubricating composite material.

2. The preparation method of the graphene / copper-based self-lubricating composite material according to claim 1, characterized in that, In step (1), the copper powder has a particle size of 15-75 μm, and the few-layer graphene powder has 3-10 layers and a specific surface area of ​​100-500 m². 2 / g.

3. The method for preparing the graphene / copper-based self-lubricating composite material according to claim 1, characterized in that, In step (1), the pretreatment conditions are as follows: heat treatment at 200-400℃ for 1-2 hours.

4. The method for preparing the graphene / copper-based self-lubricating composite material according to claim 1, characterized in that, In step (2), the volume ratio of copper powder to few-layer graphene powder is 95-99:1-5.

5. The method for preparing the graphene / copper-based self-lubricating composite material according to claim 1, characterized in that, In step (3), the thickness of the powder layer is 50-200 μm.

6. The method for preparing the graphene / copper-based self-lubricating composite material according to claim 1, characterized in that, In step (3), the conditions for the scanning and shaping process are as follows: the laser power is 100-500W, the scanning speed is 100-1000mm / s, the spot diameter is 50-200μm, and the powder layer is scanned with a checkerboard path with a line spacing of 60-100μm.

7. The method for preparing the graphene / copper-based self-lubricating composite material according to claim 1, characterized in that, In step (4), the mass ratio of the pre-composite powder to the molten copper liquid is 1:50-100.

8. The method for preparing the graphene / copper-based self-lubricating composite material according to claim 1, characterized in that, In step (4), the temperature of the molten copper liquid is 1100-1200℃, the preheating temperature of the mold cavity is 200-350℃, and the injection pressure of the high-speed injection is 50-150 MPa.

9. The method for preparing the graphene / copper-based self-lubricating composite material according to any one of claims 1-8, characterized in that, In step (5), the stress annealing conditions are as follows: stress annealing is performed at 400-550℃ for 1-3 hours.

10. A graphene / copper-based self-lubricating composite material obtained by the preparation method according to any one of claims 1-9, characterized in that, The graphene / copper-based self-lubricating composite material has a friction coefficient of 0.10-0.28, a tensile strength of over 300 MPa, and a conductivity of not less than 85% IACS.

Images