Tribochemical Lubrication of Ceramics by Carbonaceous Vapors

Abstract

Friction coefficients of less than 0.02 and negligible wear have been attained and continuously maintained in a pin-on-disc apparatus between a sapphire pin and discs of Sialon, silicon carbide, zirconia or zirconialalumina as long as a carbonaceous gas or vapor, such as ethylene, propane, benzene, or 1-propanol, was supplied to the conjunction region. Mean contact pressures were around 300 MPa and bulk temperatures were varied between ambient and 700°C. For every ceramic and vapor combination some temperature ranges exhibited high friction and wear, others very low friction and wear. Raman and Auger spectroscopies of the carbonaceous deposits formed in the wear tracks show significant differences depending on the temperature range and the feed gases or vapors supplied. In general, friction and wear reduction occurred in two steps at different rates. The tribochemistry involved is likely to comprise hydrocarbon acid-catalytic cracking at low temperatures and pyrolysis at high temperatures.