Achieving ultra-high mechanical properties in metastable Co-free medium entropy alloy via hierarchically heterogeneous microstructure

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.