The morphology and bonding characteristics of nanocrystalline diamond films prepared with different Ar:H ratios have been studied and are correlated to tribological performance. A coating made with high Ar:H ratio displayed low friction of 0.05 and very minimal wear, while the low Ar:H film showed high friction (> 0.2), rapid wear, and complete failure after 50 cycles. As both films had the same rms roughness, their different tribology appears to stem from a change in morphology.