Effect of Al addition on the microstructures and deformation behaviors of non-equiatomic FeMnCoCr metastable high entropy alloys

The phase stability, mechanical behaviors, and deformation mechanism among a series of Fe48-xMn32Co10Cr10Alx metastable high entropy alloys (HEAs) with different Al contents were systematically investigated. With the increase in Al content, the microstructures of alloys change from dual-phases of face-centered-cubic (FCC) + hexagonal-closed-packed to single-phase FCC and then to dual-phases of FCC + body-centered-cubic. The strength of the studied HEAs is related to the second-phase volume fractions in the initial microstructures. The stacking fault energy values of alloys increase with the increase in Al content. The dominant deformation mechanisms of the Al-free, 3 at. % Al, and 7 at. % Al HEAs are dislocation gliding plus martensitic transformation, dislocation gliding plus deformation twinning, and only dislocation gliding, respectively. This work is helpful to understand the physical mechanism in FCC metastable HEAs and further to develop high-performance HEAs.