We report the study of fatigue improvement for power transmission equipment in, for example, automobiles. We coated DLC(Diamond-Like Carbon)on rollers of a rolling contact fatigue tester and carried out roller pitting tests. The results showed that the DLC coating improves the life of the rollers by more than two orders of magnitude. We observed the metal structure under the DLC coating by optical microscopy, SEM(Scanning Electron Microscopy), and TEM(Transmission Electron Microscopy), and confirmed that a major cause of fatigue damage was cracks and pitting on a surface, caused by shearing force. We also found that metal nanocrystals were formed on the surface of the sample that showed a long life in the roller pitting tests. Probably that was caused by accumulation of plastic strain from repeated stress. A small friction coefficient by the DLC coating reduced shearing force, suppressed fatigue damage, and led to the formation of metal nanocrystals.
