The Effect Of Graphite Particle Size On The Properties Of Copper-graphite Composites Made With Copper-coated And Uncoated Graphite Powders Via Electroless Copper Plating

Copper-graphite composites were prepared by powder metallurgy process.The effect of graphite particle size on the microstructure, physical andmechanical properties of the composites made with copper-coated anduncoated graphite powders via electroless copper plating was investigated.The friction and wear properties were analyzed under the conditions ofdifferent combinations between friction surface, sliding direction and flakegraphite base. The combinations fall into three types, respectively A, B and C.Type A means the combination of friction surface perpendicular to press axisand sliding direction parallel to the flake graphite base, type B means thecombination of friction surface parallel to press axis and sliding directionperpendicular to the flake graphite base, type C means the combination offriction surface parallel to press axis and sliding direction parallel to thelongitudinal direction of graphite flake.Both copper-graphite and copper-copper coated graphite composites withgraphite contents of 10wt.% were prepared by pressing at 400MPa, sinteringat 950℃×2h and repressing at 600MPa. The composites have homogenousmicrostructure, a minimum density of 6.61g/cm3 and the relative density up to98.4%. The particle size of graphite has significant effect on the properties ofthe copper-graphite composites. With the particle size of graphite increased,the netlike copper matrix changes from discontinuous to continuous-skeleton,the orientation of flake graphite base tend to be perpendicular array relative topress axis, the microstructure difference of the composites intersectioned atperpendicular and parallel direction relative to press axis is more remarkable.Volume expansion of the copper-graphite composite greens occurred during石墨粒度及其表面化学镀铜对铜-石墨复合材料性能的影响sintering. The density of the sintered composites was increased afterrepressing. With the graphite particle size increased, the density, the electricalconductivity and the bending strength of the repressed composites increased,but the density of the greens decreased. The graphite powders coated byelectroless copper plating resulted in the uniform graphite distribution in thecomposites, the improvement of sintering, and the enhancement of interfacecohesion between copper and graphite, thus the decrease of the porosity andthe raise of the electrical conductivity and the bending strength of thecomposites.Dry sliding friction and wear tests were performed in a pin-on-ring modeusing three kinds of orientation combinations. It was found that thecopper-graphite composites have lower friction coefficient and better frictionstability, and wear weight losses increase linearly with an increase of slidingdistance. The copper-graphite composites with large graphite particle haveslightly higher friction coefficients but lower wear rates than that with smallgraphite particle. The wear rates of copper-copper coated graphite compositesare decreased obviously with respect to copper-graphite composites. However,the friction coefficients and fluctuation of copper-coated composites withsmall (1μm,6μm,10μm,25μm) graphite particle were increased. Thefriction coefficients and wear rates of the copper-graphite composites in typeA combination are lower than that in type B or C combination. Themorphology characteristics on the worn surface can be divided into three maintypes such as scallop, furrow and cavity. The wear mechanisms of bothcopper-graphite and copper-copper coated graphite composites includeadhesion, abrasion, delamination and oxidation. With the particle size ofgraphite increased, the dominant wear mechanism of the copper-graphitecomposites changes from abrasion to delamination. The wear mechanism ofthe copper-copper coated graphite composites tend to bedelamination-dominant.