Characterization of mechanical properties and microstructure of non-equiatomic medium-entropy alloys Fe40Mn40Co10Cr10 and Fe50Mn30Co10Cr10 in different structural states over a large temperature range

Abstract A comparative analysis was carried out to evaluate the low-temperature mechanical behavior and microstructural evolution of two non-equiatomic medium-entropy alloys: Fe 40 Mn 40 Co 10 Cr 10 and Fe 50 Mn 30 Co 10 Cr 10 , examined in both coarse-grained (CG) and nanostructured states. The results demonstrate that, unlike the CG alloy, the NS counterparts undergo a complete phase transformation from the Face-Centered Cubic to the Hexagonal Close-Packed lattice. Notably, the fraction of the hcp phase in the nanostructured state shows only a weak dependence on temperature and on the number of rotations imposed during high-pressure torsion (HPT). This finding highlights the fundamental role of severe plastic deformation in stabilizing the hcp phase, effectively overriding the temperature sensitivity observed in the coarse-grained alloys. The comparison underscores that nanostructuring not only alters the phase balance but also homogenizes the response of Fe 40 Mn 40 Co 10 Cr 10 and Fe 50 Mn 30 Co 10 Cr 10 alloys under cryogenic and ambient conditions, pointing to the dominant influence of grain refinement and defect density in driving phase stability.