The influence of initial roughness and circular axial run-out on friction and wear behavior of Si3N4-Al2O3 sliding in water

Recently, it has been shown that water-lubricated sliding of Si3N4 against Al2O3 can result in steady-state friction coefficient values as low as 0.004. However, most experiments were performed using extremely polished surfaces and did not consider the effect of circular axial run-out of the discs, which could be important in practical applications. In this paper it was investigated the influence of these parameters on the ultra-low friction coefficient (ULFC) phenomenon, including correlations with running-in. Greater initial surface roughness and circular axial run-out resulted in greater running-in duration and wear. In addition, the transition of wear mode from mechanical to tribochemical dominated as a function of sliding distance was clarified and it was proposed that a mixed lubrication regime is required for ULFC to occur.