Tribological behavior and lubrication mechanism of self-lubricating ceramic/metal composites: The effect of matrix type on the friction and wear properties

This study aims at revealing the mechanisms of how matrix type and lubricant content affect the lubricating properties of graphite doped self-lubricating composites. Self-lubricating mechanism and tribological properties of three kinds of lubricating materials having different matrix-types (copper alloy, zirconia and alumina) are investigated. Results show that the effect of matrix type on the friction and wear properties of the composites is mainly related to its hardness and binding property with graphite. The variation of matrix-type causes significant changes in the degree of difficulty for extruding lubricants onto the friction surface from the material interior and plastic deformation resistance of composites, thus affecting the formation of lubricating and transferring films, and wear mechanisms of the materials. For copper alloy matrix that has low hardness and binding force with graphite, incorporating just a little graphite can greatly promote its lubricating performance. By contrast, alumina-graphite composite is difficult to achieve good lubrication when the graphite content (volume fraction) is less than 15% because of a relatively high hardness and brittleness of alumina matrix. Based on these analyses, we formulated some principles to design self-lubricating ceramic/metal composites.