Interaction of DLC and B4C coatings with fully formulated oils in boundary lubrication conditions

Diamond-like carbon (DLC) and Boron Carbide (B4C) coatings are promising candidates for sliding-rolling contact parts, especially gears to increase scuffing load capacity and prolong lifetime. Generally, commercially available fully formulated oils are compatible with ferrous surfaces, but normally have not been optimised for coatings. In this study, the tribological properties of tungsten carbide containing DLC (WC-DLC), hydrogenated DLC (H-DLC) and B4C coatings against steel ball with two fully formulated oils in boundary lubrication conditions have been evaluated. They were compared with that of a Steel/Steel tribocouple. Interactions between lubricants and sliding surfaces were also investigated using surface characterisation techniques such as XPS and Raman Spectroscopy. It was found that Steel/H-DLC system provided the lowest friction coefficient for both oils.