Wear Mechanism of Ceramics and Surface Topography

Assuming that harder asperities sliding on a flat surface were semicylindrical with the hemispherical ends, whose surface consisted of a series of spherical micro-asperities, effects of the number of contact points n, total area S_p of the cross-sections of grooves ploughed by harder asperities and depth of plastic zone on the coefficient of friction and wear for ceramics were theoretically analyzed. To verify theory, wear tests with various ceramic pins and a Si₃N₄ disk were carried out at a sliding speed of 1.63 m/s and under load of 0.98 N with no lubrication. The sizes of wear scratches on the worn surfaces were measured by means of a Talysurf and SEM photographs. The wear rates of the pins and Si₃N₄ disks increased with an increase in the mean cross-sectional area S_p/n of the scratches. This trend agreed with the theoretical results, which also showed that the S_p values were proportional to the wear rates. Theory also indicated the existence of a new criterion applicable to estimation of the wear rate.