Superhard nanocomposite Ti–Si–C–N coatings prepared by pulsed-d.c plasma enhanced CVD

Ti–Si–N coatings have been investigated widely in recent years due to their unique nanocomposite microstructure and attractive properties of superhardness, fairly good oxidation-resistance nearly to 1000 °C, etc. For this study, complex quaternary Ti–Si–C–N coatings were deposited on HSS substrate at 550 °C using an industrial set-up of pulsed-d.c. plasma enhanced chemical vapor deposition technique from TiCl4/SiCl4/H2/N2/CH4/Ar mixtures. The composition of the films could be controlled well through adjustment of CH4 flow rate and the mixing ratio of the chlorides. Detailed structural and chemical characterizations using transmission electron microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) suggest formation of a Ti(C,N)/a-C/a-Si3N4 nanocomposite structure. Ti(C,N) films show (200) texture which change to random orientation of the crystallites when the silicon content reaches about 9 at.%. Depth-sensing indentation measurement on coatings reveals that the hardness of coatings increases from 30 to 48 GPa with increasing Si and C content. These coatings show surprisingly high thermal stability and retain their hardness, even after annealing to 800 °C.