Transition from static to kinetic friction of unlubricated or oil lubricated steel/steel, steel/ceramic and ceramic/ceramic pairs

Tribological tests were conducted on different pairs of the bearing steel 100Cr6 and a commercial alumina under unlubricated and oil lubricated conditions where the transition behaviour from static to kinetic friction as a function of surface finish and contact pressure was of particular interest. Static and kinetic friction were measured using a laboratory tribometer with ball-on-plate geometry at an extremely low tangential speed of 8.3 μm/s applied to the plate specimen. Results showed a significant effect of surface finish on both the static and kinetic coefficients of friction as well as on the transition behaviour. Transition behaviour was strongly dependent on the materials mated. The self-mated steel pairs showed greater values of kinetic than static coefficient of friction while no significant difference of both friction values was measured on self-mated alumina pairs with ground plate specimens. Influence of oil lubrication on static friction was small compared with that on kinetic friction where the last one was substantially reduced by oil lubrication with 100Cr6/100Cr6 and 100Cr6/Al2O3 pairs, particularly. Stick-slip effects occurred with both unlubricated and lubricated pairs under high normal loads and depending on surface finish.