Nanostructure influence on DLC-Ag tribological coatings

Addition of diamond like carbon (DLC) phase to Ag-base overlay prepared by ECR–DC hybrid sputtering was found to reduce its coefficient of friction compared to that of the substrate material in dry sliding. The coefficient of friction, tested in dry conditions, of the Ag matrix overlay decreased by sp3-rich C formation. It decreased from 0.72±0.05 to 0.25±0.05 by increasing the graphite/Ag target area ratio from 1/9 to 5/5 at low sliding speed (0.01 ms−1), 5 N load in dry sliding. Its drastic decrease was found when the grain size of the prepared films was lower than 10 nm as measured by transmission electron microscopy (TEM). The prepared coatings were characterized also by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and atomic force microscopy (AFM).