Tribological properties of hydrogenated amorphous carbon under dry and lubricated conditions

•Graphitisation occurs due to rubbing under dry condition and promotes a-C:H wear.•Gear oil significantly suppresses graphitisation and decreases wear of a-C:H.•a-C:H/steel contact has tribolayers of a-C:H- and additive-derived products.•Tribolayers of a-C:H/steel are highly wear resistant than those of steel/steel.

Diamond-like carbon (DLC) coatings are considered as potential surface coatings for many engineering applications including gears and engine parts. It is important to know whether conventional extreme pressure (EP) additive-containing oil can work with DLCs and provide tribological performance as effective as they provide on steel surfaces. This study examines the friction and wear properties of hydrogenated amorphous carbon (a-C:H) under dry, base oil (BO)- and fully formulated gear oil (FF)-lubricated conditions. Pronounced graphitisation occurs due to rubbing under dry condition and provides low friction but promotes wear. However, BO and FF greatly suppress graphitisation and wear. Tribofilms formed from FF in a-C:H/steel contact appear to exhibit superior antiwear properties than those formed in steel/steel contact.

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