Unbalanced magnetron sputtered Ti-Si-N:MoS_x composite coatings for improvement of tribological properties

Development of nanocomposite coatings attracted great interest in the past few years. The Ti-Si-N nanocomposite coatings demonstrated superhigh hardness and thermal stability. The tribological performance of these coatings, however, was often under expectation in comparison with that of conventional coatings such as TiN, due to their high friction coefficients. It is desired to incorporate lubricant elements into these coatings without significantly sacrificing their mechanical properties. In this work, Ti-Si-N composite coatings incorporated with MoS_x were deposited using unbalanced magnetron sputtering. The MoS₂ was co-sputtered and served as lubricant element to reduce the wear friction coefficient. The results showed that with a small amount of MoS₂ incorporation (less than 5 at.% of Mo), the tribological properties of the as-deposited composite coatings were significantly improved with little influence on their superhigh hardness. Both the friction coefficient and wear rate decreased monotonously with increase of the Mo content. It is interesting to note that for the coating with only about 1 at.% of Mo content, the friction coefficient and wear rate were abruptly reduced to about 1/2 and 1/3 of those without MoS₂ incorporation, respectively. When the Mo content was increased up to about 5 at.%, the wear rate of the coating could be reduced to about one tenth in comparison with the coatings without MoS₂ co-deposition.