Study On The Preparation And Friction And Wear Properties Of Copper-based Self-lubricating Composites

Copper matrix self-lubricating composites possess good mechanical,physical and chemical properties of metal matrix and excellent tribological properties of solid lubricants,which are suitable for chemical,electrical,high and low temperature,heavy load,high vacuum,strong radiation and so on.Revealling the friction and wear mechanism of copper matrix self-lubricating composites,developing a new method of quantitative characterization of the key features of friction surfaces,and establishing relevant models are the key problems that need to be solved in the design and application of metal-based self-lubricating composites.In this paper,the Cu-Mo2S and Cu-W2S self-lubricating composites were prepared by power metallurgy hot pressing process.the microstructure evolution and friction and wear behavior of the two materials were studied.The friction model of metal matrix self-lubricating composite is established and verified.The details were shown as follows:(1)The effect of MoS2 content on the friction and wear properties of Cu-MoS2 composites was studied.MoS2 was very effective in reducing the friction coefficient of copper matrix composites when the content of MoS2 was less than 20 vol%.When the content of MoS2 is added further,the friction coefficient can hardly be reduced,which is related to the covering area of the MoS2 lubricating film on the worn surface.The MoS2 lubricating film was formed by a large number of peeling MoS2 nanoparticles.The coverage area of MoS2 nanoparticles on the worn surface increased with the increase of MoS2 content,and the content of MoS2 on the outermost surface was much higher than that of the composite material,which was caused by the slip of layered MoS2 crystals during friction.(2)The effects of WS2 content and annealing temperature on microstructure evolution,mechanical and tribological properties of Cu-WS2 composites were investigated.A large number of W and Cu2S appeared in most WS2 particles after annealing at 700℃ and 800℃.The effect of WS2 on reducing the friction and wear of Cu-WS2 composites is remarkable.The friction coefficient of Cu matrix decreases from 0.76 to 0.2 when 10 vol%WS2 is added,and the wear rate of Cu-40 vol%WS2 composites is much lower than that of pure copper.After annealing at 900℃and 950℃,the friction coefficient of Cu-20 vol%WS2 composites increased from 0.2 to 0.5.The wear rate of the composites annealed at 700℃ was the highest.The severe plastic deformation of the friction layer could lead to the parallel arrangement of the WS2 sheets in the sliding direction.It is beneficial to the formation of lubricating film and crack propagation under friction surface,and the main wear mechanism is delamination.(3)The worn surface of Cu-MoS2 composites was analyzed by XPS technique.It was found that the coverage area of MoS2 film on the worn surface of Cu-MoS2 composites decreased from the friction surface to the matrix,which was consisted of a large number of MoS2 thin sheets less than 200nm.The coverage of MoS2 film on the outermost surface is 2.9-6.2 times that of the substrate.The coverage of MoS2 film is exponentially related to the volume content of MoS2.This is why adding too much lubricant does not significantly reduce the friction coefficient.The relationship among friction coefficient,lubricant film coverage and lubricant volume fraction was successfully established,and the friction model of metal matrix self-lubricating composite was verified.