Influence of surface morphology on the tribological behavior of diamond- like carbon coating

Diamond-like carbon (DLC) films were prepared on top of hard coatings, namely, prior to the DLC deposition, CrN, TiCN and nanocomposite nACo (nc-AlTiN/(a-Si3N4) layers were deposited on WC-Co substrates. The R-a roughness of WC-Co substrates was 0.05 and 0.2 mu m. Surface morphology of DLC coatings was investigated by means of profilometry and geometrical parameters R-a (average roughness), R-sk (skewness), R-ku (kurtosis) and R-z (mean peak to valley height) were evaluated. Fretting tests were conducted with 3 mm in diameter alumina balls under 1 and 2 N load, at slip distance of 2 mm and frequency of 2 Hz. Statistical analysis shows significant correlation between R-a and R-z parameters corresponding to initial DLC surface and wear scar surfaces produced by fretting tests after 2400 and 4800 cycles, respectively. This finding indicates a relationship between friction (wear) and R-a and 12, parameters. Positive correlation between the coefficient of friction (COF) and kurtosis R-ku indicates that surface flatness is an important factor for optimal friction of an alumina ball against DLC coating.