Towards Self-Lubricating Effect of In Situ Iron Tungstate in Rubbing WC/Mn13 Steel Cermet against a HSS Steel

We study the mechanism of formation of the multilayer structure of the subsurface regions of WC/Mn13 steel cermets after sliding on a steel disk at speeds from 10 to 37 m/s and contact pressure of 5 MPa in order to elucidate the fundamental role of the processes of tribooxidation on a worn surface in the formation of the tribomechanical properties of a large family of similar W/Fe-containing materials. It was shown that the maximum antifriction effect of WC/Mn13 steel cermets under conditions of high-speed sliding was due to in-situ generated FeWO4 that provided friction coefficient drop from ~0.17 to ~0.07 when sliding at 10 and 37 m/s, respectively. The sliding speed had its effect on the subsurface structure and tribolayer thickness, so micron-sized, mechanically mixed 3–4 μm-thick layers (MML) were generated in sliding at 10 and 20 m/s, whose wear occurred mainly by subsurface fracture and delamination of tile-shaped wear particles. Continuous tribolayers with 10–15 μm thickness were generated at 30–37 m/s with underlying zones containing fragmented and deformed WC grains. Such a structure provided plasticizing effect during sliding so that wear was mainly by flow of so plasticized subsurface layers.