Abstract: A new metastable dual-phase Fe₅₉Cr₁₃Ni₁₈Al₁₀ medium entropy alloy (MEA) with hierarchically heterogeneous microstructure from micro- to nano-scale was designed in this work. Partially recrystallized FCC phase and lots of NiAl-rich B2 precipitates are obtained by annealing and aging treatment. The yield strength of the MEA at room temperature (298 K) and liquid nitrogen temperature (77 K) increased from ∼910 MPa and ∼1250 MPa in the annealed state, respectively, to ∼1145 MPa and ∼1520 MPa in the aged state, while the uniform elongation maintained more than 15%. The excellent mechanical properties of the MEA both at 298 and 77 K are attributed to the co-activation of multiple strengthening mechanisms, including fine grain, dislocation, precipitation, transformation-induced plasticity, stacking faults, and nano-twins.

Key words: Medium entropy alloy, Precipitation strengthening, Heterogeneous microstructure, Transformation-induced plasticity, Mechanical properties