Understanding of Mechanical Behavior of FeMnCoCr High Entropy Alloy Nanowire with Varying Mean Grain Size: An Atomistic Approach

Molecular dynamics (MD) simulations were employed to investigate the mechanical properties and deformation mechanisms of Fe50Mn30Co10Cr10 high-entropy alloy (HEA) nanowires (NWs). Seven polycrystalline samples with varying mean grain size (MGS) ranging from 3.98 to 20.97 nm were subjected to simulated tensile testing. Results demonstrate that the sample with the largest MGS (20.97 nm) exhibits a combination of the highest strength and remarkable ductility among the simulated samples. This enhanced strength stems from high dislocation density and the pinning effect of Hirth dislocations. Concurrently, the exceptional ductility is attributed to a reduction in Stair-rod dislocation density, a face centered cubic (fcc) to hexagonal close packed (hcp) phase transition, and the formation of deformation twins. For the sample with the smallest MGS (3.98nm), high ductility arises from both phase transformation and amorphization. Furthermore, during deformation the surfaces of NWs function analogously to grain boundaries (GBs) as defect nucleation sites, while additionally serving as preferential nucleation sites for necking during fracture. These findings provide significant insights into the grain size dependence of mechanical properties in HEA NWs and elucidate the underlying deformation mechanisms.