MECHANISM OF TRANSFER FILM FORMATION DURING REPEAT PASS SLIDING OF CERAMIC MATERIALS

The formation of transfer film and the consequent effects on the friction and wear behavior of ceramic materials during repeat sliding contact were studied. This was done using four structural ceramics, namely silicon nitride, silicon carbide, alumina and zirconia, with a cylinder-on-flat test configuration. The transfer film consists of reattached fine wear debris particles, the film, whenever formed, is strongly attached, enough to resist being wiped off by the slider. Calculations suggest that the fine particles are attached primarily by van der Waals forces and to a lesser extent by electrostatic attractive forces. As a consequence, the formation of transfer film leads to a decrease in the wear rate because of the `protecting' role of the film. The presence of the film at the contact interface also results in high friction. The presence of a liquid environment and/or surface active species reduces the particle adhesive forces and hence can inhibit the formation of a transfer film.