Ultrastrong and ductile metastable Fe-rich medium-entropy alloy with high-density nanolamellar L12 precipitates

Abstract

An Fe-rich medium entropy alloy (MEA) with a composition of Fe41.9Ni34.4Co11.3Cr2.3Al6.9Ti3.2 (at. %) has been successfully developed by utilizing transformation-induced plasticity (TRIP) and high-density L12 nanolamellae to achieve ultrahigh yield strength (YS) and decent ductility. The aging treatment not only resulted in the precipitation of L12 lamellae, but also led to the enrichment of Fe, Co, and Cr into the fcc phase, creating a mechanically metastable fcc matrix. The metastable MEA strengthened by nanolamellar L12 precipitates exhibits an ultrahigh YS of ∼1.44 GPa, an ultimate tensile strength of ∼1.64 GPa, a uniform elongation of ∼22 %, and a total elongation of ∼31 %. The findings may provide a new approach for developing ultrastrong and ductile high/medium entropy alloys.