Nanocomposite TiC/a–C:H hard coatings deposited by reactive PVD

Thin films of titanium carbide and amorphous hydrogenated carbon at various compositions have been deposited by unbalanced reactive magnetron sputtering from a metallic titanium target in the presence of argon and acetylene. XRD probed the presence of nanocrystalline TiC and, at high titanium concentrations, of metallic titanium. The XPS examinations allowed one to determine the amount of TiC produced at any concentration of titanium. Raman spectroscopy proved the presence of a-C:H up to 38 at.% of titanium. The coatings have a pronounced hardness maximum of 35 GPa at a composition of approximately 80% TiC and 20% a-C:H. The hardness at 60% TiC and 40% a-C:H as well as that of 100% TiC does not exceed 18 GPa. The mean separation of the crystallites, whose diameter is approximately 4 nm, amounts to a few atomic distances. At the maximum hardness a coefficient of friction of 0.25–0.3 is obtained. The coatings thus provide, at the optimum composition, high hardness at low friction.