Hetero-deformation-induced (HDI) plasticity induces simultaneous increase in both yield strength and ductility in a Fe50Mn30Co10Cr10 high-entropy alloy

Low yield strength is the bottleneck of the face-centered cubic-structured high-entropy alloys (HEAs). Here, the strategy of hetero-deformation-induced (HDI) plasticity is applied by hetero-structuring to induce strengthening and strain hardening for a simultaneous increase in both yield strength and ductility in a Fe50Mn30Co10Cr10 HEA. The coarse-grain (CG) microstructure is a dual phase consisting of face-centered cubic (γ) and hexagonal close-packed (ε) phases, along with phase transformation from γ to ε to happen during tensile deformation. The hetero-structure (HS) was designed, besides recrystallized γ and ε, specifically to reserve a part of deformed γ after cold rolling followed by incomplete recrystallization. Yield strength increases from 200 MPa in CG to 760 MPa in HS, while uniform elongation (i.e., ductility) increases from 35% to 38%. The tensile load-unload-reload testing showed the ceaselessly presence of hysteresis loop during each unload-reload cycle. Both the residual plastic strain and HDI stress were measured with tensile strains in both HS and CG, providing solid evidence of the effect of HDI plasticity. To be specific, the HDI stress is found to account for a large proportion of global flow stress in HS as compared to that in CG. It turns out that the HDI plasticity facilitates both HDI strengthening and HDI strain hardening, which play the crucial role in enhancing strength and ductility. The microstructural origin of HDI plasticity in HS was ascribed to plastic incompatibility at hetero-interfaces of among varying grains as evidenced by the evolution of Schmid factor and KAM values as well.