Deformation and annealing behaviors of as-cast non-equiatomic high entropy alloy

Abstract

The recently developed non-equiatomic high entropy alloy (HEA), Fe80-xMnxCo10Cr10, overcoming the strength-ductility trade-off. Phase stability in Fe80-xMnxCo10Cr10 is reduced via tailoring Mn content, resulting in a single phase or dual-phase microstructure (face-centered cubic (FCC) phase and hexagonal close packed (HCP) phase). In this work, the plastic deformation and annealing behaviors during processing in two as-cast non-equiatomic HEAs with coarse grains, i.e., Fe30Mn50Co10Cr10 with single-phase (FCC) and Fe60Mn20Co10Cr10 with dual-phase (FCC+HCP), are investigated by a combination of electron back-scattered diffraction and transmission electron microscope. Plastic strain of Fe30Mn50Co10Cr10 is mediated by dislocation slip via forming interacting planar arrays of dislocations, {111} deformation twins and micro-shear bands. In Fe60Mn20Co10Cr10, it is revealed a synergy of multiple deformation mechanisms, involved dislocation slip and transformation induced plasticity (TRIP, FCC→HCP). More interestingly, it is revealed {101¯2} deformation twins and ε martensite plates with the special misorientation (70.5°/<112¯0>) in the HCP phase. This work further confirms Mn content can act as a switch for TRIP effect in Fe80-xMnxCo10Cr10 HEA. Upon annealing treatments, profuse annealing twinning boundaries in Fe30Mn50Co10Cr10 and dense boundaries with 70.5°/<112¯0> in Fe60Mn20Co10Cr10 are formed, paving the way for the development of HEA with the superb mechanical performance.