Research On Preparation And Tribological Properties Of Copper Matrix Graphite Composites With Electric Current

Copper matrix graphite composites converge good contact lubricity, low thermalexpansion coefficient characteristics of graphite and high conductivity, goodscalability characteristics of copper to a wonderful performance that good conductivity,wear resistance, arc erosion. It can be a ideal materials for sliding electrical contactparts, the study of friction and wear property under electric current provides theoreticalsupport for the development of new electrical contact material.Copper matrix graphite composites were prepared by the powder metallurgicalmethod with the graphite plated by copper, and the mechanical properties of thecomposites were studied; the experiments were carried out on a pin-on-disc tribo-testerwith copper matrix graphite composites/QCr0.5couples. The effects of plating copper,graphite particle size and content, sliding-velocity and current density on tribologicalproperties were investigated by way of single factor experiment. With the help ofmorphologies of friction surface, the wear mechanism of composites under differentworking conditions were examined. The results of the studies were listed as follows.Copper plating graphite can significantly enhance the interfacial combinationstate of the copper/graphite, it improves the density and conductivity of the composites,and decreases the brinell hardness; it also reduces the friction coefficient and qualitywear rate under current-carrying friction.Smaller particle size graphite can remarkably split the copper matrix,it causes thereduction of density, conductivity, brinell hardness; because of the equally distributionin the matrix, graphite reduces arc stimulation and the friction coefficient and qualitywear rate under current-carrying friction.The density, conductivity, brinell hardness of composites reduce with theincreasing of graphite content. And the friction coefficient and quality wear rate alsodecrease under current-carrying friction, when the content exceeds10wt%, the qualitywear rate keeps a low range, the graphite content of composites that has best tribological performance at sliding velocity of40m/s is12.5wt%.Effect of surface roughness, temperature and lubricant condition changed bytesting conditions on friction and wear properties under current-carrying is significantimpact. The friction coefficient increases with the sliding-velocity raising and thereducing of current density, and the quality wear rate rises with the increase of velocityand current density.The wear mechanism of composites under current-carrying friction is a compositemechanism that coupling to mechanical wear and electrical wear, adhesion, abrasion,electrical wear are simultaneous. Wear process can be classified to three typical statesby differences of working conditions, that were slight wear state，medium wear stateand severe wear state, and each wear state has its dominant wear mechanism. At theslight wear state, the graphite equilibrium makes a good antifriction and anti-arc effect,slight adhesion occurs on the friction surface; at the medium wear state, severeradhesion, slight abrasion and arc erosion are dominant; serious electrical wear occursat the severe wear state, the copper melts down, the graphite ablates off, and thefriction surface fails.