Simultaneously enhancing the strength and strain hardenability by Si substitution in metastable high-entropy alloys

We have demonstrated the potential to simultaneously enhance the strength and strain hardenability of metastable dual-phase high-entropy alloys (HEAs) by substituting the constituent transition metal element with Si. This leads to the development of a face-centered cubic single-phase Fe₅₀Mn₃₀Cr₁₀Si₁₀ HEA with excellent strength-ductility synergy, low density and low alloying costs. The substantial solid-solution hardening effect achieved through Si-alloying leads to a higher yield stress for this HEA compared to its dual-phase counterpart when their grain sizes are comparable. In addition, the Si-alloying imparts a low stacking fault energy (∼12.8 mJ/m²) to this HEA, facilitating the progressive formation of hexagonal close-packed martensite plates during plastic deformation. Furthermore, the Si-alloying increases the volume fraction of the deformation-induced martensite plates (up to 75.5%) and renders their thickness ultra-thin (<20 nm), thereby leading to remarkable strain hardenability.