Tribochemical investigation of DLC coating tested against steel in water using a stable isotopic tracer

Tribochemical reaction of DLC coating in water was investigated using a stable isotopic tracer, heavy water (deuterium oxide, D2O), in which the friction test of DLC coating and 440C ball pair was carried out. The worn surfaces were analyzed by ToF–SIMS. For comparison, a test was also conducted in ion exchanged water (H2O). The result showed that tribochemical reaction between DLC and D2O occurred, and CD, OD groups were formed on the worn DLC surface. It is suggested that OD groups mainly combine with the secondary or tertiary carbons on the surface. It is considered that the formed hydrophilic hydroxyl groups play an important role in reducing the friction and wear of DLC coating and the counter part in a water environment.