Tribological characteristics of DLC and Si-containing DLC films deposited by electron beam excited plasma (EBEP)-CVD

Tribological behavior of diamond-like carbon (DLC) and Si-containing DLC films deposited by an electron beam excited plasma (EBEP)-CVD system is investigated for applications to mechanical components. The ball-on-disc tests against SUJ2 with dry and oil-lubrication under several sliding conditions have been performed for DLC and Si-containing DLC coated carburized-SCM420 discs. Under dry-lubrication, the Si-containing DLC-coated discs prepared with SiH4, flow ratios of 2.8 and 12.5% show lower coefficients of friction than a DLC-coated disc at disc temperatures from room temperature to 120 degrees C. The Si-containing DLC at a 36.4% SiH4 flow ratio reveals high friction and wear because it includes an amorphous SiC structure. Under oil-lubrication, the coefficients of friction of the coated discs are lower than that of the uncoated disc, and the Si-containing DLC displays lower friction than the DLC. Remarkably these tendencies have appeared under mixed lubrication. Ball-on-disc tests at oil temperatures from room temperature to 120 degrees C show that the Si-containing DLC has a low coefficient of friction of 0.06 and that wear is not detected under boundary lubrication. An optimal surface roughness exists for the lubricating condition to obtain a lower coefficient of friction.