Influence of EP additive concentration on the tribological behaviour of DLC-coated steel surfaces

This investigation indicated that the life of boundary lubricated DLC-coated surfaces involves several stages. After running-in, the DLC coating, although unable to form a tribofilm on top of the coating, takes an active part in forming a low friction tribofilm on the uncoated steel counterpart or on the exposed steel substrate, which eventually leads to the final wear out of the coating. Further, the concentration of additive has a significant influence on the tribological behaviour of DLC-coated steel surfaces. Contrary to the common rule for steel/steel contacts, reduction of the EP additive concentration may lead to improved tribological behaviour of DLC-coated surfaces.