Achieving strength-ductility balance in a casting non-equiatomic FeCoNi based medium-entropy alloy via Al and Ti combination addition

Abstract

The conflict of strength and ductility has always been a huge challenge when developing advanced structural materials. The introduction of nano-scaled precipitates into metallic materials through composition design is a well-established method for achieving the strength-ductility balance. Herein, a series of non-equiatomic FeCoNi based medium-entropy alloys (MEAs) with Al and Ti combination addition were prepared by vacuum induction melting, and its phase constitution, microstructural changes and mechanical properties were systemically studied. The microstructure of Al/Ti co-doped alloys are composed of BCC phase + FCC phase + L21 nanoparticles structure, in which the L21 nanoparticles are homogeneously distributed and coherent with matrix. By tailoring Al/Ti ratio, the as-cast Ni0.6CoFe1.6 MEA presents a good strength-ductility combination. Among them, the Al0.2Ti0.1 MEA possesses higher yield strength of 837.7 ± 18.9 MPa and ultimate tensile strength of 1305.4 ± 22.0 MPa, as well as maintains an acceptable failure strain of 12.3 ± 0.7%. The improvement of yield strength is originated from the contributions of the precipitation hardening, grain boundary strengthening, and solid solution strengthening. The present study provides a new avenue to design strong yet ductile MEAs for industrial applications.