Tribological testing of DLC coatings for automotive applications

Abstract: In this work, the friction and wear behavior of three DLC coatings was evaluated in various conventional and alternative fuels as well as in commercially available formulated engine oils and additive-free synthetic oil. The first DLC has a thin top-coating of hydrogenated amorphous carbon (a-C:H), the second consists of Si-doped DLC (a-C:H:Si) and the third is a W-doped multilayered structure of a-C:H and a-C:H:W. The tribological tests were performed using a ball-on-flat reciprocating rig at low contact pressures. Methods such as white light interferometry (VSI), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), Raman spectroscopy, transmission electron spectroscopy (TEM) and electron spectroscopy for chemical analysis (ESCA/XPS) were used for analyzing and characterizing the coatings and counter surfaces in an effort to gain an understanding of the tribological mechanisms involved.