The influence of carbon content on the microtribological performance of W-S-C films

Abstract

The layered structure of transition metal dichalcogenides makes them promising materials for self-lubricating films. Transition metal dichalcogenide films can be considered as substitute for carbon-based self-lubricating films in several varieties of environmental conditions. The tribological properties of these films at high load have been studied extensively. However, the tribological behaviour of these films in the milli-Newton load range relevant for micro-electro-mechanical systems has hardly been reported. In the present work, the microtribological response of W-S-C coatings deposited by reactive sputtering is investigated. For that purpose, W-S-C coatings with various concentrations of carbon were deposited on steel substrates using magnetron sputtering. The friction and wear of these coatings are determined as function of applied load and carbon content. The results show that, even though the wear of these films increases with applied load and decreases with carbon content, the friction coefficient is minimum for the films containing the highest amount of carbon at low and intermediate load. It is maximum for the films containing minimum carbon at the highest load. There is no evidence for a transfer layer on the worn surfaces.