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

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.