FCC twins and martensites responses of metastable dual-phase high entropy alloy to friction stir processing

Fe₅₀Mn₃₀Co₁₀Cr₁₀ dual-phase high entropy alloy (DP-HEA) has good application prospects in the nuclear and automotive industries due to its strength-ductility synergistic effect. The initial volume fractions of FCC twins and HCP martensites in Fe₅₀Mn₃₀Co₁₀Cr₁₀ HEA affect the relative contribution of transformation-induced plasticity and twinning-induced plasticity to the alloy's strength and ductility under loading conditions. Understanding the relationship between FCC twins and martensites is crucial during the friction stir process (FSP). In this study, the microstructure of Fe₅₀Mn₃₀Co₁₀Cr₁₀ HEA as FSP condition was studied. The HCP phase in the base metal almost completely transformed into the FCC phase during FSP. Both FCC twin and HCP martensite transformations serve to alleviate strain in the FCC matrix. The initiation of FCC twin and martensite formation depends on critical stress levels at different temperatures. Higher strain and coarser grains promote more martensite formation, while finer grains and lower strain impede it, causing FCC twins to occur before HCP martensites during the cooling process of materials in the processed zone. These findings offer insights into controlling the volume fractions of twins and martensites in FSPed DP-HEA, thereby potentially enhancing the mechanical properties of DP-HEA.