Probing the low friction mechanisms of WC/a-C films under low humidity conditions

Developing a carbonaceous transfer film on the counterpart surface leads to a C/C strong adhesive interface, which dominates the friction behavior of hydrogen-free carbon-based films in low-humidity environments, ultimately resulting in high friction. This research illustrated that WC/a-C films can accomplish low friction under low humidity conditions, a performance not attainable for hydrogen-free carbon-based films. To clarify the low friction mechanisms, a comparative investigation was conducted on the frictional characteristics of a-C, WC/a-C:H, and WC/a-C films. Contrary to two prevalent lubrication hypotheses of ‘friction-induced graphitization’ and ‘passivation’ mechanisms in carbon-based films, the establishment of an intrinsic weakly adhesive C/WO₃ sliding interface was identified as a critical factor contributing to the low friction of WC/a-C films.