Tribological characteristics of Si-containing diamond-like carbon films under oil-lubrication

Tribological behaviors of Si-containing diamond-like carbon (DLC) and DLC films deposited by an electron beam excited plasma (EBEP)–CVD system were investigated for applications to mechanical components. The ball-on-disc tests against bearing steel with oil-lubrication were performed for the Si-containing DLC and the DLC-coated carburized Cr–Mo steel discs. Two different oils with and without zinc dialkyldithiophosphate (Zn-DTP) additives were used as lubricants. The Si-containing DLC films deposited at SiH4 flow ratios of 2.8 and 12.5% showed low coefficients of friction and wear resistance when lubricated in the oil with additives. The results from X-ray photoelectron spectroscopy (XPS) analysis indicated that it was due to the effect of formation of a boundary lubrication film including ZnO, ZnS, FePO4, FeS and FeS2 compounds on the lubricated contact region.