Multiscale boundary frictional performance of diamond like carbon coatings

This paper investigates the frictional performance of a PECVD hydrogenated undoped DLC coating and the alternative super-finished gear steel surface pairs. A tribometer replicates the conditions found in the conjunction of a performance racing transmission spur gear pair. In mixed and boundary regimes of lubrication the DLC contact is shown to have a lower coefficient of friction despite having comparable surface topography when measured using optical interferometry. To determine the mechanisms responsible for improved friction of DLC coated tribo-pairs atomic force microscopy is used. It is shown that the nanoscale surface topography of the investigated PECVD DLC coated pairs reduces the real asperity contact area formed at the same load carrying capacity. This highlights a contributing mechanism for improved friction with the DLC coating.