Self-lubricating W-S-C-Cr tribological coatings deposited by r.f. magnetron sputtering

Abstract

Tribological coatings composed of transition metal dichalcogenides (TMD) have long been studied for their excellent self-lubricant properties. However, they exhibit low load-bearing capacity, and their performance tends to deteriorate significantly in the presence of humidity. In previous works, doping disulfides and diselenides of tungsten and molybdenum has proven to be a way of greatly improving the tribological performance of this class of films in different environments. In this work, thin films were deposited by r.f. magnetron sputtering on silicon and steel samples, using two targets (carbon and chromium) and tungsten disulfide pellets. The final composition was controlled by the number of WS2 pellets and the ratio of the power applied to the targets. The carbon content was fixed at approximately 40 at.% in all depositions. The chromium content in the coatings was varied in the range 0 – 13.5 at.% and the S/W ratio was approximately 1.25 in all compositions in the series. The coatings were characterized in regard to their hardness, adhesion, chemical composition and bonding, microstructure and morphology, as well as their tribological behaviour.