Grain-scale microtribological behavior of VCoNi medium-entropy alloy

The tribological behavior of equiatomic face-centered cubic (FCC) VCoNi medium-entropy alloy (MEA) remains underexplored despite of the alloy’s notable tensile strength and ductility. In this study, the tribological performance of VCoNi MEA is investigated using microscratching techniques, with emphasis on the effects of grain orientation, normal force, and scratch velocity. The study has demonstrated that the grain orientation in VCoNi MEA determines the activation of slip systems during the scratching processes, which significantly affects the morphology of wear tracks, slip steps and pile-up, as well as changes in microtribological behavior. As the normal force increases, the degree of wear intensifies, which is attributed to the significant material pile-up and more intense plastic flow. The plastic deformation of VCoNi MEA is found to be independent of scratch velocity within the 0.1–2 µm/s range. Ploughing and micro-shearing are identified as the primary wear mechanisms under various friction conditions. Furthermore, during the ploughing process, the deformation mechanism of the alloy is still dominated by dislocations. The direction of dislocation motion aligns with the direction of pile-up resulted from plastic deformation. The present study offers critical insights into the tribological behavior of medium-entropy alloys and broadens the potential for their applications in friction-intensive environments.