Mechanical and tribological properties of TiC/amorphous hydrogenated carbon composite coatings fabricated by DC magnetron sputtering with and without sample bias

TiC/amorphous hydrogenated carbon (a-C:H) composite films were deposited by Ti DC magnetron sputtering using argon and acetylene as the carrier gas and precursor, respectively. The working pressure was maintained at 4 x 10(-1) Pa and the composition of the films was modulated by controlling the partial pressure of acetylene. The composition and structure of the films were evaluated by X-ray photoelectron spectroscopy and glancing angle X-rays diffraction, whereas the hardness and elastic modulus values of the films fabricated using different sample biases were measured by nano-indentation. Ball-on-disk tribometry was used to measure the tribological properties, and secondary electron microscopy was used to analyze the wear tracks. The results show that the friction coefficients and wear rates do not vary significantly with the Ti concentrations when the Ti concentration is above 39.7 at.% or below 20 at.% but increase with increasing titanium concentrations between 20 at.% and 39.7 at.%. The wear mechanism depends on the relative amounts of TiC and a-C:H. At high Ti concentrations, the mechanism resembles that of TiC due to the thin a-C:H matrix surrounding the TiC grains. At low Ti concentrations, the mechanism is similar to that of DLC as the effects of the a-C:H matrix dominates over those of the TiC grains. (c) 2006 Elsevier B.V. All rights reserved.