Nanostructured TiC/a-C coatings for low friction and wear resistant applications

Closed-field unbalanced and balanced magnetron sputtering was used to deposit nanocrystalline TiC (nc-TiC)/amorphous carbon (a-C) nanocomposite coatings with hydrogenated or hydrogen-free a-C matrix, respectively. The contents of Ti and C in the coatings have been varied over the full range of interest (7-45 at.% Ti) by changing the flow rate of acetylene gas or the locations of substrates relative to the center of C/TiC targets. Different levels of bias and deposition pressure were used to control the nanostructure. The nanocomposite coatings exhibit hardness of 5-35 GPa, hardness/E-modulus ratio up to 0.15, wear rate of 4.8×10−17 m3/N m lap, friction coefficient of 0.04 under dry sliding and strong self-lubrication effects. The nanostructure and elemental distribution in the coatings have been characterized with cross-sectional and planar high-resolution transmission electron microscopy (HRTEM) and energy-filtered TEM. The influence of the volume fraction and size distribution of nc-TiC on the coating properties has been examined.