Unveiling the unique bifunctionality of L12-structured nanoprecipitates in a FeCoNiAlTi-type high-entropy alloy

Abstract

Nanoprecipitation strengthening has been widely adopted as an effective way to design high-strength alloys, which generally leads to the loss of ductility. Here we unveil the unique bifunctionality of L12-structured nanoprecipitates in a FeCoNiAlTi-type high entropy alloy (HEA), enabling the combined increase of tensile strength and ductility. Results show that as-quenched precipitate-free matrix alloys undergo thermally-induced martensite transformation and form the body-centered cubic (BCC) martensite phase with limited tensile ductility. In strong contrast, when introducing the dense coherent L12-type nanoprecipitates, the face-centered cubic (FCC) matrix is temporarily stabilized, which in turn promotes the microbands-induced plasticity associated with stress-induced martensite transformation upon deformation. This allows us to achieve significantly improved work hardening capability and excellent plastic deformation stability at a high-strength level. These new findings reshape our understanding of the precipitation strengthening and could provide useful guidance for developing high-performance alloys by regulating the coherent nanoprecipitate and martensitic phase transformation.