| Graphene reinforced copper-based self-lubricating composite combine the high thermal conductivity of copper and the high mechanical strength,wear resistance of graphene,and have broad application prospects.However,graphene is easily agglomerated in the preparation process,and the bonding strength with the copper matrix is poor,not only weakening the mechanical properties,but also affecting the formation of the graphene self-lubricating transfer film in the friction process,thereby reducing the graphene copper-based self-lubricating composite performance.In order to solve this problem,the graphene-coated copper particle composite powder was prepared by one-step reduction using molecular-level mixing method.The composite was uniformly dispersed.Then,the graphene-copper-based composite material was prepared by hot-press sintering,and the graphene-copper-based composite was studied in detail.Material preparation process,morphology structure and wear mechanism.(1)Preparation of powders by molecular-level mixing method:Graphene oxide was first prepared,and the number of layers was lower than four,and then graphene copper-based composite powders were prepared by one-step reduction of ascorbic acid using a molecular-level mixing method as a reducing agent.The difference in pH will affect the morphology and uniformity of the composite powder.At pH=8,the uniformity of the composite powder is best.The analysis of the composite process of graphene and copper by molecular-level mixing method showed that graphene not only coated on the surface of copper particles,but also embedded in the copper particles.With the increase of graphene content,the coating effect on copper particles is more complete.(2)The bulk graphene copper matrix composites were fabricated by vacuum hot-press sintering.It was found that the addition of graphene hinders the growth of copper particles during the sintering process.With the increase of the graphene content in the powder,the graphene changes from a random distribution to a network-like distribution in the copper matrix,and the grain growth of copper is also suppressed.The graphene network structure provides a fast load transmission channel for the composite material.Even if the graphene content is increased to 2.0 wt%,the hardness and compressive strength of the composite material are still higher than pure copper by 39%and 17%,respectively.(3)When the load is 5N,10N,the friction coefficient and the wear rate of the composite material decrease with the increase of the graphene content.The self-lubricating transfer film formed during the friction of the composite material effectively improves the wear resistance of the composite material.When the load condition is 20N,the friction coefficient and wear rate of the composites decrease first and then increase with graphene content.Adding more than a certain amount of graphene will cause the mechanical properties of the composite material to decrease.When the load exceeds the range of the composite material,it is difficult to form a continuous dense transfer film,and the anti-wear and anti-wear properties of the composite material begin to decrease.The lwt%content of graphene composites has the best comprehensive performance.It not only has excellent lubricity and wear resistance,but also has no deterioration in mechanical properties.It has better friction reduction and wear resistance than composites prepared by ball milling.It shows that the lubricity matches the mechanical properties,specialty.(4)A preliminary study on tantalum-doped graphene-copper based composites was conducted.The cerium-doped graphene copper-based composites were prepared by molecular-level mixing and high energy ball milling.The hardness of the composites prepared by the two methods has been greatly improved,but the friction performance is not ideal and the density is low.The probable reason is that tantalum and copper are refractory systems,and it is difficult to make it dense using the same sintering process as the graphene copper matrix composite. |
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