Adsorption and tribo-chemistry aspects of nc-(W,Ti)C/a-C(Al) film with oil addition under boundary lubrication

To achieve an appropriate lubricating film under boundary and mixed lubrication, designing the interface between the solid and liquid phases is very important for the application of inert DLC coating on engine components. In this paper, nanocomposite coatings nc-(Ti,W)C/a-C(Al) were prepared. Combined with the oil additive DMTD, the coatings exhibited excellent boundary-lubricated friction performances under a wide load range. Through the theoretical calculation, as well as X-ray photoelectron spectroscopy (XPS) and gas chromatography (GC) analysis, a two-stage friction decrease mechanism was proposed: adsorption induced friction reduction under low load and tribo-chemical reaction induced friction reduction under high load. We hope this work would be instructive for designing optimum coating-additive composite system for industry applications.