Effects of carbon incorporation in tungsten carbide films deposited by r.f. magnetron sputtering: single layers and multilayers

Tungsten carbide coatings with different carbon content have been obtained by r.f. magnetron sputtering from a sintered pure WC target on high-speed steel. Two different sputtering deposition processes were tried in order to deposit tungsten carbides with two stoichiometries: one with pure Ar, and the other one with a reactive Ar/CH4 mixture. Single tungsten carbide coatings obtained with pure Ar show a cubic WC1−x phase with a strong (2 0 0) crystallographic orientation, while single coatings deposited with the reactive mixture of gases show a (1 1 1) preferred orientation. Multilayer structures were also deposited by sequentially changing the sputtering gas composition between both single layer deposition conditions. The bilayer period was thus varied from 100 to 10 nm. SIMS analysis confirmed the coatings multilayer structure. XRD analysis of the multilayers shows a combination of the orientations obtained for single layers with a progressive decrease of (2 0 0) orientation when decreasing the bilayer period. Nanoindentation, microscratch and ball-on-disk tests were performed over all the coatings to compare their mechanical and tribological properties.