Or0404—Effect of a Tribochemical Reacted Film on Friction and Wear Properties of DLC Coatings

Abstract

AbstractDiamond‐like carbon (DLC) coatings provide low friction properties without lubricants and, with lubricants, should provide super low friction. In this study, the friction and wear properties of DLC coatings with lubrication in the sliding contact area were evaluated to find an environmentally friendly material combination that can provide super low friction (i.e., a coefficient of friction lower than 0.01). The friction and wear properties of a steel pin on a DLC coated disk with lubrication were evaluated by using environmentally friendly fluids (organic acid or alcohol) as lubricants. In a sliding test of tetrahedral amorphous carbon (ta‐C) lubricated with DL (a mixture of dextrorotatory and levorotatory molecules)‐lactic acid, a super low coefficient of friction (0.01) was obtained at the end of the test and was much lower than that of an uncoated disk and an amorphous hydrogenated carbon (a‐C:H) disk. The coefficient of friction obtained with DL‐lactic acid was lower than that seen for acetic acid or glycerol. The ta‐C disk lubricated with DL‐lactic acid showed a small wear scar width. The main reason for the reduced friction and wear is probably attributable to the formation of a tribochemical reacted film in a tribochemical reaction with the acid. An oxidation film (white colored layer) of FeO also formed on the mating pin under DL‐lactic acid lubrication in the sliding contact area. These results showed not only the difference in the adsorbed lubricants due to the chemical structure of DLC, but also that the oxidized condition of the steel pin influenced the coefficient of friction.