The Influence of Material Roughness, Hardness and Lubricant Additives on Micropitting Behaviour in Rolling-Sliding Contacts

Regarding micropitting, which is one of the fatigue damages that occur under conditions where the oil film thickness is smaller than the surface roughness, the effects of hardness and roughness of the test piece and differences in lubricants were confirmed. Endurance tests and friction tests were conducted using two-disc test rig. On the condition with harder and rougher surface of test pieces, deeper micropits were produced. The phosphorus additive blended oil led to a shallower pit depth than the sulfur additive blended oil. It was further suggested that the friction coefficient had little effect on micropit progress, and the influence of the lambda ratio (ratio of the oil film thickness to the root mean square roughness) after initial running-in was large. In a surface of high hardness and high roughness, micropitting tend to progress more easily. However, it was found out that the progress can be suppressed by suitable lubricants additives.