Micro-wear and friction of carbon film with molecularly thin PFPE lubricants

When a surface protective diamond-like-carbon (DLC) film experiences high speed contact, it can be degraded and damaged by mechanical stress and frictional temperature rise. In this study, the thermomechanical contact behavior of thin DLC film on a magnetic recording disk was systematically investigated with respect to the contact speed (1.2 m/s ~ 36.1 m/s) using a newly-developed experiment technique. For comparison, experiments were performed on the DLC film samples with and without molecularly thin perfluoropolyether (PFPE) lubricants on the surface. Using the post experiment samples, atomic force microscopy (AFM) and micro Raman measurements were carried out to examine the mechanisms of surface wear and material degradation. It was observed that the higher contact speed (12.0 m/s & 36.1 m/s) caused earlier failure and wider wear track on the surface than the lower contact speed (i.e., 1.2 m/s). When a monolayer thick PFPE lubricant is applied onto the surface, it significantly improved the friction and wear performance of the DLC film. Based on the Raman analysis, it could be found that the DLC on the contact area showed a clear evidence of thermal degradation, i.e., graphitization process, by frictional heat generation.