Wear transitions and mechanisms in lubricated sliding of a molybdenum coating

Wear tests were performed for a Mo coating sliding against bearing steel specimen under boundary lubrication conditions. Results were compared with (i) hardened carbon steel sliding against bearing steel and (ii) Mo coating sliding against boron cast iron. Tests indicated that the wear resistance of the Mo coating was superior to that of the uncoated hardened steel. The initial surface topographies of the coatings were suitable to facilitate the transfer of the applied load directly onto the phases and prevented the softer phase directly involved in the wear process. The morphology of the transfer layer formed on the Mo coating was identified by X-ray diffractometry. And the layers were expected to supply an in situ lubrication effect. The wear rates of the coating against a steel slider were lower compared with those worn against a cast iron slider. With increasing applied load, the probability of the harder phases crack and fracture increased until the fraction of the unfragmented phases on the contact surfaces was no longer adequate to support the load. The dominant wear mechanisms in each wear regime were discussed.