Hierarchical microstructure enables high strength and good ductility in as-cast Fe27Ni35Cr18.25Al13.75Co2Ti2Mo2 high-entropy alloy

Abstract

As-cast alloys often require complex thermomechanical processing to obtain a hierarchical structure to achieve a good combination of strength and ductility. Here in this work, a novel hierarchical Fe27Ni35Cr18.25Al13.75Co2Ti2Mo2 high-entropy alloy (HEA) with ultra-high tensile strength and excellent ductility was fabricated by direct casting. The as-cast alloy exhibits hierarchical structure with an ultrafine lamellar microstructure (ULM), ultrafine rhombus microstructure (URM), ultrafine vermicular microstructure (UVM), nanosized precipitates and spinodal decomposition (SP) that develops during casting and cooling. The incompatibility of face-centered cubic (FCC) and body-centered cubic (BCC) phases in the deformation process leads to heterogeneous deformation-induced (HDI) hardening, which brings the alloy a tensile yield strength (YS) of ∼1056 MPa, an ultimate tensile strength (UTS) of ∼1526 MPa and a total elongation (El) of ∼15.6%. Additionally, the numerous interfaces generated by the hierarchical structure absorb the energy during deformation, effectively retarding the dislocation motion and causing strong work-hardening.