Wear behaviour of tetrahedral amorphous diamond-like carbon (ta-C DLC) in additive containing lubricants

Diamond-like carbon (DLC) coatings offer excellent mechanical and tribological properties. They provide ultra-low friction and superior wear resistance. In recent years, the research of DLC coating focuses on the application of these coating in mechanical components which work under boundary lubricated conditions. Since conventional lubricants and lubricant additives were formulated for metal surfaces, the effects of these lubricants on DLC contact and interaction between lubricant additives and DLC surfaces are still unclear. In this work, we present the influence of lubricant additives and counterbody materials on the wear behavior of ta-C DLC coating under boundary lubrication conditions. Tribological tests were performed in a home-build pin-on-disc tribometer. Atomic Force Microscopy (AFM), Field Emission Scanning Electron Microscopy (FESEM), Nano-indenter, X-ray Photoelectron Spectroscopy (XPS), Raman spectroscopy and scanning white light interferometry were used for characterization of ta-C DLC and worn surface analysis. The results show that ta-C DLC were totally wear out in DLC/steel contact tested in base oil. Addition of lubricant additives into the base oil significantly reduced the wear in the DLC/steel contact. ta-C DLC exhibited totally different wear behavior in DLC/steel and DLC/DLC contact depending on lubricant formulation. It is concluded that combination of lubricant formulation and counterbody material is a crucial factor for the use of DLC in lubricated conditions. •Additive containing oils provide better wear protection than base oil for ta-C DLC.•Passivation of either ta-C or steel surfaces is a crucial factor for wear resistance.•ZnDTP provides better wear protection than GMO for DLC/steel contact.•GMO provides better wear protection than ZnDTP for DLC/DLC contact.•GMO+ZnDTP together do not have synergistic correlation for wear protection.