ROLLING-CONTACT-FATIGUE WEAR CHARACTERISTICS OF DIAMOND-LIKE HYDROCARBON COATINGS ON STEELS

Adherent diamond-like hydrocarbon (DLHC) coatings were applied on AISI M-50, 52100, 4118 and 440C steel rods by using an approximately 0.2 m um amorphous-silicon-hydrocarbon (a-SiHC) bonding layer between the DL HC and the steel. Both the a-SiHC and DLHC coatings were applied using a single, broad-beam ion source. The rods were subjected to rolling-c ontact-fatigue (RCF) testing under high, cyclic Hertzian stress (5.5 G Pa), low lubricant-film-thickness parameter (lambda=0.7) conditions. O rder-of-magnitude increase in the fatigue lives of all four rod materi als were observed. Systematic RCF tests coupled with microscopic exami nation after various test intervals show that micro-polishing by hard DLHC coating fragments may play an important role in prolonging fatigu e lives. Raman spectroscopic measurements suggest that cyclic stressin g of the DLHC layer causes it to transform from what was initially amo rphous carbon into the more lubricous and stable graphite phase.