In this article, a systematic study is carried out to assess the influence of lubricant additives on the durability of a hydrogenated diamond-like carbon (DLC) coating under mixed rolling/sliding contact is provided. Experiments were performed in a mini traction machine using a DLC (15 at.% hydrogen) coated disc on an uncoated steel ball at 50 per cent sliding/rolling ratio and in a motorized cylinder head (Ford Zetec) cam/follower test rig. Five different lubricants containing zinc dialkyldithiophosphate (ZDDP) and/or friction modifiers (Moly Dimer (MD)/Moly Trimer (MT)) were used. This study reveals that the lubricant additives have a strong influence on the coating durability while ZDDP additive effectively reduces wear to extremely low levels. The addition of the MT additives only has a marginal effect on wear, whereas the MD additive substantially reduces the performance. The mechanisms by which the additives affect the wear in this ultralow-wear regime are discussed.
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