Grain size-dependent phase-specific deformation mechanisms of the Fe50Mn30Co10Cr10 high entropy alloy

The present work reports the effect of initial microstructures (i.e., the material annealed at 600 °C (A600) with the fine grain single FCC phase vs. the material annealed at 900 °C (A900) with the coarse grain FCC/HCP dual phase) on deformation mechanisms, damage resistance, and mechanical properties of the Fe50Mn30Co10Cr10 HEA. The strength of A600 is higher than A900, and the ductility of both materials is similar with the total elongation exceeding 50%. A900 shows a higher strain hardening rate than A600 below 0.2 true strain, which could be attributed to simultaneous deformation accommodation from the FCC/HCP dual phase. The FCC grains mainly exhibit deformation-induced HCP phase transformation while the HCP grains show multiple deformation mechanisms, i.e., various slip modes (Shockley partial dislocations, perfect dislocations, extended dislocations, and dislocations present on prismatic planes), the HCP to FCC reverse transformation, the formation of kink bands. The strain hardening rate of both materials is similar above 0.2 true strain, which could be related to higher TRIP kinetics of A600 than A900. The A600 shows the refinement of the crack size due to its fine size of grains and HCP phase. The superior damage resistance could lead to the large ductility of A600 even in the presence of the non-recrystallized areas in its initial microstructure. The present work could provide microstructure design solutions for metastable HEAs with superior strength-ductility combination and damage resistance.