Behaviour of boundary lubricating additives on DLC coatings

The additive molybdenum dithiocarbamate formed a low friction film on both DLC surfaces, with lower friction on the graphitic than on diamond-like carbon one. Atomic force microscopy (AFM) measurements showed that this was due to the formation of regions of low lateral force on asperities within the rubbed track. ZDDP provided some reduction in friction on both DLC surfaces after rubbing but did not form thick ZDDP tribofilms like those generated on steel surfaces.