Effect of tricresyl phosphate on wear of silicon nitride sliding against bearing steel

Wear tests of a silicon nitride ball pressed against a bearing steel rod were carried out at room temperature under lubrication with a light mineral oil using a lathe. The wear of the Si3N4 ball was measured at various fixed sliding distances up to a maximum distance of 3000 m. A mineral oil of low viscosity (base oil), and a mineral oil containing different amounts of phosphorus (added as tricresyl phosphate) and 0.2 wt.% S were supplied to the contact region between the Si3N4 ball and the steel rod. An addition of 0.5 wt.% P to the base oil reduced the wear volume of the Si3N4 ball by about 90% of that with the base oil. The reduction in the wear is ascribed to surface film formation. When using the base oil alone, the wear of the Si3N4 ball decreased more at high sliding velocities than at low sliding velocities.