Diamond-like carbon-coated Ti6Al4V: influence of the coating thickness on the structure and the abrasive wear resistance

Diamond-like carbon (DLC) coatings of 0.7, 1.5 and 3.0 μm thickness were deposited on the titanium-alloy Ti6Al4V by a direct current discharge using benzene as gaseous precursor. Scanning electron microscopy, Raman spectroscopy, atomic force microscopy were utilised for gaining information about the micro-structural features and the composition. Hardness measurements, scratch and simple abrasion wear tests (ball-cratering apparatus with an abrasive fluid) were carried out for describing the tribological performance of the DLC. The fractures cross-sections of the DLC seems to be featureless and smooth. The universal hardness (HU) amounts to values of between approximately 12.8 and 22.2 GPa and the Young’s modulus of between nearly 133 and 213 GPa. Raman spectroscopy points microstructural changes in dependence of the coating thickness. Although, the cohesive failure of the DLC is dependent on the coating thickness, the DLC spallation at the lateral edges of the scratch occurs at approximately 35 N for all coatings. The worn surfaces exhibit a very heterogeneous DLC damage due to the abrasive loading which also points to the micro-structural differences within the DLC film.