Effect of carbon content on structure and properties of WCN coatings prepared by RF magnetron sputtering

WCN coatings with carbon content ranging from 0 to 19.2 at.% were deposited by reactive magnetron sputtering technique. The structure, mechanical, tribological properties and corrosion performance were investigated by XPS, XRD, SEM, HRTEM, nano-indentation CSM, ball-on-disk tribo-meter, AFM, Bruker 3D Profiler and corrosion testers. The results show that the incorporation of carbon does not affect the cubic structure. WCN coatings consist of WCN and amorphous C and CNx phases. The incorporation of carbon results in the crystallite size refinement and the decrease of the average roughness. The H, H/E and H3/E2 ratios of WCN coatings first increase and then decrease and the maximum values are 36.7 GPa, 0.110 and 0.30 GPa, respectively, at 14.8 at.% C. All the H, H/E and H3/E2 ratios of WCN coatings are higher than that of W2N coating. The friction coefficient and wear rate of WCN coatings first decrease and then increase with increasing the carbon content. The friction coefficient and wear rate are mainly related to the lubricant wear debris. Moreover, the hardness and the ratios of H/E and H3/E2 also have a certain influence on the wear rate of the coatings. The corrosion resistance of the substrate which coated with W2N or WCN coatings is superior to the bare substrate. The corrosion resistance of the W2N coating is improved by doping some carbon content.