The cobalt-free Fe35Mn15Cr15Ni25Al10 high-entropy alloy with multiscale particles for excellent strength-ductility synergy

The evolution of microstructure and tensile properties of a newly designed cobalt-free high entropy alloy, Fe35Mn15Cr15Ni25Al10 (at.%), has been investigated during the annealing and aging processes. A dual-phase alloy with a face-centered cubic (FCC) and body-centered cubic (BCC) or ordered B2 structure, along with multiscale heterogeneous precipitates, has been formed. The precipitated phases consist of bulk primary B2-NiAl and secondary BCC/B2 particles that range in size from the nanometer to micrometer scale. By prolonging the aging time, the yield strength is strongly enhanced, increasing from 250 MPa to 860 MPa at the peak aging stage. The primary sources of strengthening are precipitation hardening and hetero-deformation-induced strengthening from the BCC or ordered B2 phase. Furthermore, the incorporation of various strengthening mechanisms and high-strain hardening capability at cryogenic temperatures (77 K) results in improved strength and ductility simultaneously. A highly cost-effective high-entropy alloy, doped with a high concentration of aluminum, has been developed.