MICROFRICTION STUDIES OF MODEL SELF-LUBRICATING SURFACES

Self-lubricating composites consist of at least one structural (matrix) phase and at least one phase to provide lubrication. Modelling the behavior of such composites involves ascertaining the frictional contributions of each constituent phase under varying conditions of lubricating film coverage. The ORNL friction microprobe, a specialized microcontact tribometer, was used to investigate the frictional behavior of both matrix and lubricant phases in order to support the development of self-lubricating surfaces. Polished chemical-vapour-deposited SiC deposits and silicon wafers were used as substrates. The wafers were intended to simulate the thin SiO2 films present on SiC surfaces at elevated temperatures. MoS2 in both sputtered and burnished forms was used as the model lubricant. The effects of the chemical-vapor-deposited SiC substrate surface roughness and method of lubricant film deposition on the substrate were studied for single passes of a spherical Si3N4 slider (NBD 200 material). In contrast to the smooth sliding exhibited by burnished films, sputtered MoS2 surfaces exhibited marked stick-slip behavior, indicating that the frictional behavior of solid lubricating coatings can be quite erratic on a microscale, especially when asperity contacts are elastically compliant.