Self-lubrication and wear behavior of TiC/a-C:H nanocomposite coatings

Advanced TiC/a-C:H nanocomposite coatings have been produced via reactive deposition in a closed-field unbalanced magnetron sputtering system. In this paper, we report on the tribological behavior of TiC/a-C:H nanocomposite coatings in which ultra-low friction is tailored with superior wear resistance, being two properties often difficult to achieve simultaneously. In-situ monitoring the wear depth at nanometer scale reveals that the self-lubricating effects are induced by the formation of transfer films on the surface of ball counterpart. In addition, the CoF of TiC/a-C:H nanocomposite coatings decreases with decreasing relative humidity. This phenomenon can be interpreted in terms of water molecule interactions with the wear track. The influence of the volume fraction and grain size of TiC nanocrystallites on the coating properties has been examined. A superior wear resistance at a level of 10^-17 m ³/(N m lap) has been achieved under the condition of super-low friction and high toughness, both of which require fine TiC nano-particles (e.g. 2 nm) and a wide matrix separation that must be comparable to the dimensions of the nano-particles.