Phase formation and microstructure in sputter-deposited Ti-Mo-C and Ti-W-C thin films

Ti-Mo-C and Ti-W-C films were deposited by cosputtering from carbide targets in order to examine the phase formation, microstructure, and mechanical properties. A series of Ti-Mo-C films were deposited, with compositions ranging from TiC to Mo2C. The X-ray diffraction (XRD) analysis showed that multiphase Ti-Mo-C films, containing the (Ti,Mo)C, Mo2C, and Mo3C2 phases, were only obtained in highly Mo-rich films. The transmission electron microscopy (TEM) analysis showed a higher defect content in single-phase alloy Ti-Mo-C films in comparison to TiC alone. The hardness for most Ti-Mo-C films was in the range of 8 to 10 GPa, but even lower values were obtained in the multiphase films. Ti-W-C films deposited by cosputtering of TiC and WC formed only (Ti,W)C solid solutions. The X-ray photoelectron spectroscopy (XPS) analysis of peak positions showed that the W 4f(7/2) binding energy decreased with increasing W content. The hardness of most of the Ti-W-C coatings was in the range of 15 to 17 GPa; however, a sample with 40 pct W had a hardness of 29 GPa. The TEM analysis of this sample revealed an extremely small grain size and a higher film density. The high hardness of this specimen is attributed to Hall-Petch strengthening.