Surface Roughness Effects on the Properties of Silicon-Doped Diamond-like Carbon Coatings

This paper evaluates surface roughness effects on the properties of a-C:H:Si coatings obtained using plasma-assisted chemical vapor deposition (PACVD). Prior to coating deposition, the surfaces of the samples were subjected to grinding (Ra = 0.25) and then polishing (Ra = 0.05) or sandblasting (Ra = 1.41). Microscopic observations, measurements of thickness, wettability, surface topography, and tribological tests were used to characterize the substrate. The coating microstructure, thickness, and chemical content were investigated using scanning electron microscopy with energy dispersive spectroscopy (EDS). The geometric structure of the surface was examined using confocal microscopy before and after tribological tests. Tribological studies used a ball-on-disk sliding configuration in reciprocating motion under dry friction and cutting oil lubrication. The values of the contact angles were indicative of surface hydrophilic characteristics. Compared with the sandblasted surfaces, the adhesion strength of the coatings deposited on the polished surfaces was found to be higher. The coatings contributed to the improvement of friction and wear parameters. Under dry friction, a-C:H:Si coating friction coefficients and linear and volumetric wear on the polished surface were reduced compared with the sandblasted surface, respectively, by 10%, 83%, and 85%. In addition, the lubricant contributed to reducing the friction coefficients of the coating applied to the sandblasted sample compared with the polished sample without the coating by about 94%. Microscopic observations of wear traces allowed the determination of wear mechanisms; in the case of Ti13Nb13Zr, it was tribochemical wear through oxidation, while in the case of coatings, scratching and microcutting dominated.