Tribological properties of silicon nitride ceramics coated with molybdenum films under boundary lubrication

The tribological behaviour of Si 3N 4 ceramics, with and without molybdenum films deposited by means of ion beam mixing (IBM), was investigated on a reciprocating friction tester under boundary lubrication. Paraffin oil containing 3 wt.% tricresyl phosphate (TCP), sulfide olefin (SO), chlorinated paraffin (CP) and zinc dialkyldithiophosphate (ZDDP) additives were used to lubricate the ceramics. SEM, EPMA and XPS were used to examine the rubbed surfaces. It was found that concurrent use of the IBM modification and additives reduced the friction of the tribosystem and wear of blocks, and in particular reduced the wear volume of blocks by a factor of 30 with SO lubrication. The wear mechanism and synergistic effects are discussed.