Nanotribological Investigation of Sliding Properties of Transition Metal Dichalcogenide Thin Film Coatings

Abstract

Transition metal dichalcogenide (TMD)-based coatings are known for their low friction performance, which is attributed to the formation of a tribolayer consisting almost exclusively of pure well-ordered TMD. However, the formation of such a tribolayer and its wear track coverage is still unknown. In this study, we employed surface mapping and nanotribological techniques to study the properties of the wear tracks of composite W-S-C coatings. Our analysis revealed that the as-deposited coating consisted of two phases, with significantly different nanoscale frictional properties. We attributed the phases to nanocrystalline WS₂ (low friction) and amorphous solution of carbon and WS₂ (high friction). The two phases wear at different rates, especially at lower loads, where we observed faster depletion of nanocrystalline WS₂. In the wear track, sparse flat WS₂ flakes were identified, suggesting that the recrystallization of the WS₂ phase occurs only at the spots where the contact pressure is the highest.