Comparison of interface mechanics characteristics of DLC coating deposited on bearing steel and ceramics

The load response of a coating and substrate system was built using interface mechanics theory. The characteristics of interface mechanics of diamond-like carbon (DLC) coatings deposited on bearing steel (M50) and ceramics (silicon nitride, Si₃N₄) were calculated, where the results showed that Si₃N₄ substrate could bear greater stresses along the interface than M50 under similar surface load and DLC coating conditions. Since the elastic modulus of ceramics is greater than that of the steel's, when a thicker coating is deposited, there will be a greater increase of interface normal stress for ceramics than for steel, as well as a greater elastic modulus of coatings meaning a greater interface normal stress. The interface transverse stress can be small when the difference of elastic modulus between coating and substrate is minor, meaning a better match. From the scratch test results, the interface bonding capacity of DLC coating with Si₃N₄ and M50 substrate were verified.