Microstructure and tribological behaviour of super-hard Ti–Si–C–N nanocomposite coatings deposited by plasma enhanced chemical vapour deposition

Abstract

In this study, a series of new quaternary Ti–Si–C–N nanocomposite coatings have been deposited on HSS substrate at 550 °C using an industrial set-up of pulsed direct circuit plasma enhanced chemical vapour deposition (PECVD) equipment with a gas mixture of TiCl 4/SiCl 4/H 2/N 2/CH 4/Ar. The composition of the coatings can be controlled through the adjustment of CH 4 flow rate and the mixing ratio of the chlorides. Detailed structural and chemical characterisations using transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) suggest the formation of a Ti (C, N)/a-C/a-Si 3N 4 nanocomposite structure. Ti (C, N) films show a (200) texture, which change to random orientation of the crystallites when the silicon content reaches about 9 at.%. The tribological behaviour of these coatings was investigated at room and elevated temperature. The results show that the nanocomposite Ti–Si–C–N coatings with low Si and high C contents have a lower friction coefficient of 0.17–0.35 at room temperature. The Ti–Si–C–N nanocomposite coating containing 12 at.% Si and 30 at.% C shows excellent tribological properties with a low friction coefficient of 0.30 and a low wear rate of 4.5 × 10 5 mm 3 N − 1 m − 1 at 550 °C.