Friction and wear characteristics of surface in sliding contact under lubricant-free and mixed lubrication conditions were determined in the case of applying DC voltage (10 V, 10 A) by taking into account the state of oxide films forming between sliding surfaces and effect of Joule heat. It was found that under dry sliding and mixed lubrication conditions oxidation proceeded on the anode side, and on the cathode side, oxidation was controlled or a tendency toward reduction appeared. In particular, under dry sliding conditions, where oxidation was notable, and under severe contact and normal sliding conditions, oxidation was not practically observed on the block surface if it was used as an anode. Also, wear of the block surface differed with the specific electric resistance and proceeded in the region of contact by surface protrusions where the current density grew high and lubricant provided insulation. Mechanisms of running-in, in the case of large electric currents, were almost same under both dry sliding and mixed lubrication conditions. For example, in the case of electrification by using the block as an anode on the stationary side oxidation of the ring surface, controlled oxidation on the block surface and reduction occurred simultaneously. The phenomena were explained by the softening of surface protrusions by Joule heat generated by friction and wear proceeding under lower friction conditions.
展开▼
