Nanomechanical and boundary lubrication properties of titanium carbide and diamond-like carbon nanoperiod multilayer and nanocomposite films

To develop a new low friction and wear resistant coating, nanometer period TiC and DLC multilayer films composed of titanium carbide and hydrogen-free diamond-like carbon (DLC) layers were deposited by bias rf sputtering. Nanoperiod multilayer films were deposited by controlling the opposing time of the substrate to each of the titanium carbide and graphite targets. Below the 6-nm target layer period, nanocomposite films with nm-scale particles were deposited. Above the 12-nm target layer period, multilayer films were deposited. The nanoindentation hardness and nanowear resistance of the nanoperiod multilayer (TiC/DLC)n films change with the layer period. The 12-nm-target-period (TiC/DLC)n film shows higher hardness and nanowear resistance. The dependence of boundary lubrication properties on target period under poly (alpha-olefin) (PAO), PAO with glycerol monooleate (GMO) and water was investigated by an oscillating tribotest. The boundary lubrication properties of the (TiC/DLC)n films are significantly improved compared with those of the DLC monolayer film. Moreover, the hard and nanowear-resistant 12-nm-target-period multilayer film shows the lowest friction coefficient and a small damage depth under boundary lubrication using PAO, PAO with GMO and water. It is deduced that the 12-nm-target-period multilayer (TiC/DLC)n film has the shortest period and the largest number of interfaces that prevent damage elongation, and it is hard and shows superior nanowear resistance.