Influence of roughness on ZDDP tribofilm formation in boundary lubricated fretting

Influence of initial surface topography on tribofilm formation in zinc dialkyldithiophosphate (ZDDP) lubricated contact was analysed. Small displacement fretting tests with sinusoidal motion were carried out in classical sphere/plane configuration. A range of surfaces with different initial roughnesses was prepared by milling and grinding processes. Tests were carried out using variable displacement method where amplitude of imposed displacement was gradually increased after every 1000 cycles from 2 to 30 μm. The surfaces after tribological tests were measured by interferometric profiler. Main findings confirm that initial roughness has a significant influence on antiwear tribofilm formation in boundary lubricated contact. Tribofilm forms faster and require less energy to activate in case of rough surface obtained by milling process than in case of smooth grinded surface. However, in contact lubricated by oil with ZDDP additive, a significant transfer of material occurred from plane to sphere specimen.