Effect of surface roughness of self-mated alumina on friction and wear in isooctane-lubricated reciprocating sliding contact

Tribological tests were carried out on a commercial Al2O3 ceramic with varied surface finishing by grinding and polishing. The effect of surface roughness on friction and wear was studied in reciprocating sliding in 2,2,4-trimethylpentane (isooctane) as well as in distilled water and air as reference. Surface roughness was characterized by using scanning electron microscopy (SEM) and stylus profilometry and roughness values were calculated from bearing ratio curves. The experimental results showed a strong difference in the influence of initial surface quality on the tribological performance in isooctane or distilled water, particularly when rougher surfaces were mated. Depending on the surface finishing, the tests run in the boundary or mixed lubrication regimes and both the friction coefficient and the wear intensity displayed a transition from high to low values after a period of running-in. This running-in was characterized by a change in surface structure and could be anticipated by proper surface finishing of the specimens before testing or by controlled running-in procedure.