Mechanical and tribological properties of Ti-DLC films with different Ti content by magnetron sputtering technique

Ti-doped diamond-like carbon (DLC) films were deposited on Si substrates at room temperature by magnetron sputtering Ti twin-target in methane and argon mixture atmosphere. The DLC films with different Ti concentrations were fabricated by varying the gas flow ratio of Ar/CH4. X-ray photoelectron spectroscopy (XPS), Raman spectra were used to analyze the composition and the microstructure of the films. The internal stress was calculated by using the Stoney equation, where the curvature of the film/substrate was measured by BGS 6341 type film stress tester. The mechanical and tribological properties of the films were systematically studied by the nano-indentor and reciprocating ball-on-disc tester, respectively. The Ti atomic concentration in the films increased from 0.41% to 8.2% as the Ar/CH4 flow ratio increased from 60/190 to 140/110. The Ti atoms exist mainly in the form of metallic-like Ti rather than TiC when Ti concentration is 0.41%, confirmed by XPS analysis. As the Ti concentration rose to 6.7%, the Ti-DLC films transformed to composite DLC films with carbide phase embedded in the DLC matrix because of the formation of TiC. As a result, the hardness is decreased, while the stress is dramatically increased. The Ti-DLC films with 0.41% Ti doping showed a relatively high hardness (13.75 GPa), low stress (0.56 GPa), extremely low wear rate (∼10-10 mm3/Nm) and low friction coefficient (0.05).