Tribological behaviour of carbon thin films against bearing steel under continuous sliding in hydrogen environment

Carbon thin films such as diamond like carbon (DLC) coatings have been studied extensively for many years and they are already utilized in applications where low friction and low wear are needed. Yet, the understanding of the tribological behaviour of the carbon coatings in hydrogen environment is limited. This study concentrates on the tribological behaviour of the hydrogen-free and hydrogenated diamond like carbon films against bearing steel under continuous sliding in hydrogen environment. The tribological experiments using pin-on-disc test rig showed that DLC coatings provide lower friction coefficient and lower wear rate than uncoated 100Cr6 when sliding against 100Cr6 pin in hydrogen environment. The hydrogen environment can however be influencing the adhesion behaviour of the DLC coatings detrimentally causing delamination of the coating. The increase in water impurity level of hydrogen does not show to affect the friction coefficient of the DLC coatings significantly. Nevertheless, based on this study it can be said that the a-C:H coatings provide more stable friction behaviour compared to the ta-C type coatings when sliding against steel pin in hydrogen environment regardless of the water impurity level.