Hierarchical coherent precipitates lead to high tensile strength in casting BCC-structured Al0.8CrNiMn2Fe2.5 high-entropy alloy

Abstract

High-entropy alloys (HEAs) with body-centered-cubic (BCC) structure usually displayed high compressive strengths, but completely brittle fractured upon tensile test at room temperature. Here, we report a directly cast Co-free Al_0.8CrNiMn₂Fe_2.5 HEA with hierarchical microstructure and high tensile strength. This low-cost HEA consists of a Fe–Cr-rich disordered BCC (A2) matrix containing uniformly distributed high-density Ni–Al-rich ordered BCC (B2) ultra-fine precipitates (∼198 nm) and secondary B2 nanoprecipitates (∼13 nm). Owing to the hierarchical coherent precipitates, the duplex BCC-structured HEA displayed a remarkable tensile yield strength of ∼907 MPa and an ultimate tensile strength of ∼1328 MPa together with an appreciable failure strain of ∼9.6 % at room temperature, which is superior to most conventional alloys and HEAs in as-cast condition. The study introduces an effective approach for fabricating alloys with nanostructures, utilizing casting methods to achieve the targeted characteristics based on a well-thought-out compositional design.