Dislocation analysis in CrCoNi medium-entropy alloy using nanoindentation and molecular dynamics simulations

Abstract This study investigates the indentation size effect (ISE), strain rate sensitivity (SRS) and incipient plasticity in CrCoNi medium-entropy alloys (MEAs) through a combination of nanoindentation experiments and molecular dynamics (MD) simulations. Microstructural characterization reveals grain refinement and twin formation dependent on processing conditions, with significant effects on mechanical response. Nanoindentation results confirm classic ISE behaviour at the microscale, but show pronounced deviations at nanoscale depths, accompanied by discrete pop-in events indicative of homogeneous dislocation nucleation. An SRS of m=0.083 and an activation volume of 40–60 b3 suggest that thermally activated dislocation glide is governed by Peierls friction rather than forest hardening. MD simulations incorporating realistic short-range order (SRO) demonstrate reduced dislocation activity and elevated critical stresses compared to randomly distributed atomic configurations. The presence of SRO modulates deformation mechanisms, suppresses phase transformation and enhances twinning-dominated plasticity. These findings highlight the synergistic role of atomic-scale chemical ordering and geometric confinement in controlling plasticity and strengthen the case for SRO-informed design strategies in next-generation high-performance alloys.