Microtribological Behavior of W-S-C Films Deposited by Different Sputtering Procedures

Abstract

Tungsten sulfide is a transition metal dichalcogenide (TMD) with excellent self-lubricating properties, and a potential candidate for coatings for MEMS applications. Its mechanical and tribological properties can be further improved by alloying it with carbon (W-S-C films). These films are commonly manufactured by sputter deposition. The present work investigates the influence of sputtering procedure on the microtribological performance of W-S-C films. For this purpose, carbon was incorporated in the films via three different ways: (1) by using a reactive gas (CH4); (2) by co-sputtering from two separate targets (WS2 and C); and (3) by sputtering from a composite target of graphite embedded with WS2 pellets. The films were characterized with scanning electron microscopy (SEM), nanoindentation, atomic force microscopy (AFM), and micro-Raman spectroscopy (RS). Reciprocating wear tests were performed on a microtribometer with steel balls as counterbodies. The worn surfaces were investigated with white light confocal microscopy, RS, and X-ray photoelectron spectroscopy (XPS). The results show that the total wear decreases with the hardness of the investigated films and increases with applied load of the tribological test. The friction coefficient at higher load is governed by the roughness of the films. At low load, the presence of graphitic carbon determines the friction coefficient. No transfer of material from the counteracting body is observed.