Superlubricity remains an active and rapidly developing field of research. This work focuses on carbon-based (CB) coatings that may exhibit superlubricity, in particular amorphous carbon and carbon nitride (CNₓ) coatings. The underlying mechanisms of friction and wear of these coatings are examined in relation to surface roughness, gaseous environment, local asperity temperature, and the temporal evolution of environmental conditions, all of which strongly affect their tribological performance. Studies by Adachi and co-workers showed that CNₓ coatings exhibit markedly different friction and wear responses depending on the gaseous environment. In some cases, CNₓ coatings display counterintuitive behavior. For example, they can exhibit a low coefficient of friction accompanied by a high wear rate. Depending on the sequence of environmental changes, these coatings may also exhibit solid superlubricity. A satisfactory theoretical explanation of these experimental findings has not yet been established. Here, the observed phenomena are interpreted using an energy-based view of friction together with the combined action of distinct friction and wear mechanisms. The analysis suggests that these coatings may exhibit superlubricity when the surfaces are superfinished and active dangling-bond sites are largely saturated.
