Microstructure and tribological properties of magnetron sputtered nc-TiC/a-C nanocomposite

In this study, nanocomposite nc-TiC/a-C coatings were deposited on polished stainless steel substrates and silicon wafers by co-sputtering of graphite and titanium targets at a low temperature of 150 °C. Atomic force microscopy (AFM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were used to investigate the morphology and structure of the coatings. The hardness and tribological properties were assessed using Nanoindentation and Tribometer. The coatings consisted of two phases: nanocrystalline of TiC embedded in amorphous matrix of a-C. With Ti content of less than 8 at.%, the coating appeared X-ray amorphous. As Ti increased to 16 at.%, nanocrystalline phase (nc-TiC) was detected. The crystallite size was in the range of 5 to 16 nm as Ti increased from 16 to 48 at.%. The maximum hardness of 31 GPa was obtained at 36 at.%Ti. In dry tribotests against stainless steel ball, the coefficient of friction was less than 0.24 as Ti was less than 36 at.%, but abruptly increased to 0.39 as Ti reached 42 at.%. Extremely low coefficient of friction of 0.046 was obtained with oil lubrication.