Elastoplastic properties of tribological layers of WC – (Fe – Mn – C) composites formed after high-speed sliding on steel

Abstract

In this work, the authors studied the elastoplastic properties of the formed tribological layers of WC – (Fe – Mn – C) composites with matrices consisting of γ-iron (containing 4 % Mn (WC – 80G20)) and γ + α′ (containing 20 % Mn (WC – 80G4)) after friction on a high-speed steel disk at contact pressure of 5 MPa and sliding speeds in the range from 10 to 37 m/s. It was established that the main factor determining the morphology of the worn surface is sliding speed. At sliding speeds of 10 and 20 m/s, finely dispersed mechanically mixed tribolayers 3 – 4 µm thick are formed. As the sliding speed increases to 30–37 m/s, the thickness of the tribolayers reaches 10 – 15 µm, and the structure consists of oxidized fragments of WC – (Fe – Mn – C) composites and FeWO4 complex oxide and does not have a sharp boundary, like the tribolayers formed at lower sliding speeds. The highest values of nanohardness (~33 GPa) and effective Young’s modulus (~523 GPa) were achieved in the WC – 80G4 tribolayer after friction at 10 m/s when the nanoindenter was embedded into agglomerates of fragmented WC grains. This contrasted with the properties of the tribolayers formed at sliding speeds above 20 m/s. The results of nanoindentation showed an obvious effect of tribochemically induced softening in the emerging tribolayer after high-speed sliding at a speed of 37 m/s. Such a layer had a composite microstructure consisting of fragmented composite components cemented in-situ by tribochemically formed FeWO4 and, in addition to antifriction properties, had an increased indentation fracture resistance.