Effect of Bias and Test Environments on Tribological Behavior of MoS₂-Ti Composite Coatings

The MoS₂-Ti composite coatings were deposited by a new hybrid high power impulse magnetron sputtering. The effect of the substrate bias and the multiple test environments on the tribological performance of the coatings was discussed. The results show that the composite coatings presented the granular surface morphology. The presence of titanium oxides from reaction of Ti with oxygen on the surface inhibited the oxidation of MoS₂. The atomic ratio of S to Mo decreased with the increase of the substrate negative bias from 0 V to -400 V. The hardness and elastic modulus reached the maximum value at the substrate bias of -300 V, due to the much denser microstructure with the smooth surface. Meanwhile, the composite coatings exhibited the lowest average friction coefficient (0.04) as well as the wear rate 10^-7 mm³/(N·m). The tribological behaviors under multiple test environments indicate that the microstructure densification of composite coatings played a key role in the lubrication performance in ambient environment, while the excellent tribological property in N₂ and various humidity conditions was greatly attributed to the effective formation of transfer film during friction tests.