Microstructural and tribological characterization of MoS2-Ti composite solid lubricating films

Sputtered MoS2 thin films provide lubrication and wear improvements for vacuum and space applications. When exposed to humid environments, however, the MoS2 films are prone to rapid deterioration by oxidation. In this study, we synthesized a composite coating, which consists of titanium metal and solid lubricating MoS2 layers by the unbalanced magnetron sputtering process. Experimental results indicate that the Ti interlayers among the MoS2-Ti composite films effectively enhance the density and stability of the film structure. Transmission electron microscopy, X-ray diffractometry, and Raman analyses reveal the amorphous nature of the MoS2-Ti coating, which contains only a short-range order within the Ti interlayers. Ball-on-disc tribotests of the MoS2-Ti composite films show a higher friction coefficient, increased wear life and microhardness, and reduced wear debris as Ti interlayers increased in thickness. In addition to its densification and strengthening effect, the Ti interlayer also reacts preferentially with oxygen to form TiO2 and thus effectively suppresses adverse oxidation of MoS2. Thus, in humid environments, the MoS2-Ti composite film is highly promising as a solid lubricant, as evidenced by its prolonged wear life and resistance to oxidation. (C) 1999 Elsevier Science S.A. All rights reserved.