How to achieve superlow friction with DLC films?

Abstract

Among diamond-like carbon coatings, hydrogenated amorphous carbon films are of peculiar interest, since some of them exhibit under vacuum coefficient of friction in the millirange, so-called “superlow friction”. This paper will review some key requirements for achieving this peculiar friction regime. Firstly, not all hydrogenated amorphous carbon films lead to superlow friction. Hydrogen content is known to be critical, but it appears to be strongly dependent on deposition process. Some mechanical properties of the films can also be correlated with friction reduction, like viscoplasticity. Secondly, formation and evolution of a transfer film on sliding counterface seems to control frictional behavior. By performing tribological experiments under controlled environment, combined with the use of “Triboscopy”, it is possible to have some clues on the evolution of the transfer film and on its relation with the friction level observed.