Role of chemical short-range order in friction and wear behaviors in medium-entropy alloy CoCrNi

Abstract

Chemical short-range order (SRO) can effectively retard the dislocation motion, allowing for a substantive hardening effect. Notwithstanding, fundamental mechanisms behind subsequent friction and wear processes at the atom level are insufficiently understood. Meanwhile, it is still a tall order to experimentally characterize this nanoscale chemical inhomogeneity. Here, through conducting hybrid Monte-Carlo (MC) and molecular dynamic (MD) simulations, the impact of chemical SRO on the friction and wear behaviors in a CoCrNi medium-entropy alloy (MEA) was investigated. The friction weakening after introducing SRO was demonstrated to be the consequence of a combination of several factors apart from a reduction in penetration depth, which encompassed a suppression of the pile-up effect and lowered densities in total and immobile dislocation ahead of tip. Meanwhile, the SRO-dependent repression of sub-surface deformation behaviors was verified to effectively improve wear resistance. Particularly, the presence of Ni-rich domains was validated to impose additional resistance to dislocations slipping toward the interior and increase the interlocking likelihood between dislocations parallel to the surface and those slipping deeper into the sub-surface, effectively weakening the sub-surface damage. In addition, a strong SRO was corroborated to further decrease friction and wear damage. These findings are expected to provide important insights into understanding chemical SRO-related anti-friction and wear-resisting behaviors in a CoCrNi MEA.