Structural superlubricity and dislocation bending behaviors of NiCoCr medium-entropy alloys with incommensurate contact

Abstract

Structural superlubricity has emerged as an effective lubrication approach to reduce friction; however, it remains elusive whether this approach can be extended to multi-principal element alloys. In this study, we comprehensively investigated the frictional behaviors of NiCoCr medium-entropy alloy (MEA) tribo-pairs using molecular dynamics (MD) simulations. A substantial reduction in friction force, by at least one order of magnitude, was observed when the sliding interface twists from 0° to 2.5°. This reduction is primarily attributed to the continuous slipping of dislocations during the friction process. Furthermore, a nearly structural superlubricity state was achieved at the twist angle of 30°, with the friction coefficients of 0.003 and the absence of dislocations, which underscores the effectiveness and universality of forming an incommensurate interface. More importantly, the comparative study between NiCoCr and pure Ni clarified the pivotal role of dislocation bending in increasing the friction force of NiCoCr MEAs at small twist angles.