Friction reduction by thermal treatment of arc evaporated TiAlTaN coatings in methane

For severe cutting applications, the reduction of friction between work-piece and tool surface is of vital importance. Within this work, the surface of arc evaporated TiAlTaN coatings was modified by the thermal treatment in methane. The modified coatings were investigated with respect to their weight gain, composition, microstructure and friction behaviour. The weight gain is attributed to the formation of an up to ~500 nm thick discontinuous carbon deposit, which consists of an amorphous layer adjacent to the TiAlTaN coating and a graphitic layer on top. The friction coefficient was reduced from 0.66 for the as-deposited coating to 0.25 after the treatment in methane, where the low friction behaviour is stable for sliding distances up to 1000 m.