The Study On Copper Alloy Graphite Composite Contain No Lead Used For Plain Bearing

Cu10Sn based graphite composites with graphite contents of0~3wt.%werefabricated by powder metallurgy method using either Cu-coated or uncoated graphitepowders. The Cu-coating process of graphite powders was carried out usingelectroless coating technique. The effects of graphite content, graphite particle sizeand Cu-coating thickness on both mechanical and tribological properties were studied.The wear mechanism were investigated at different load conditions and analyzed byscanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX).The result showed that:(1) The friction coefficient of the composites decreasedwith the increase of graphite fraction. It decreases from0.4~0.5to0.2~0.3when thegraphite fraction reached to approximately2.5wt.%. Meanwhile, the wear resistancewas also improved accompanying with graphite fraction increasing. However, theimprovement of tribological properties was at the expense of mechanical properties.The compression strength of the composites with the graphite content of3wt.%shows about50%decline than that of0.5wt.%.(2) Both the mechanical andtribological properties were improved with the increase of graphite particle size atgraphite fraction higher than1wt.%, especially at the graphite fraction of3wt.%.(3)The formation of the Cu-coating was related to mechanism of nucleus forming ofcopper rather than layer opon layer by the small copper particles. The Cu-coatingplayed an important role in improving the mechanical properties of the composites.When the Cu-coating was thin(MC: MCu＜1:1), all the properties of the Cu-coatedgraphite composites are not obvious different from the Cu-uncoated ones. While themass ratio of graphite to copper is1:1, the Cu-coated graphite composites showedabout a5to10%improvement on compression strength and15to25%on wearresistance at the applied load of100N. The density and relative density were alsoimproved. However, due to the low hardness and relative density, the tribological andmechanical properties of Cu-coated graphite composites decreased with furtherincreasing the Cu-coating thickness.(4) The main wear mechanism was mild abrasivewear at low applied load (30,50N), severe abrasive wear at high applied load (100N),severe adhesive wear at low graphite content (lower than1wt.%) and mild adhesivewear at high graphite content (higher than2.5wt.%). In addition, fatigue wearoccurred in the case of small graphite particle size (20μm) and thick Cu-coating (MC:MCu=1:2). Applied load and graphite content were the chief factors on wear mechanism. All composites showed the same wear mechanism but different degrees.