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

<title>Abstract</title> <p> 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. </p>