Nanotwinned precipitates induced ultra-strong AlCoCrFeNi2.1 eutectic high-entropy alloy through additive manufacturing

Modulating the secondary phase is a key approach to enhancing the mechanical properties of metallic materials, relying heavily on processing methods and alloy composition. Here, we harness the extreme printing conditions of laser-based powder bed fusion to create a non-equilibrium microstructure dominated by the B2 phase in an AlCoCrFeNi_2.1 eutectic high-entropy alloy (EHEA). A simple post-heat treatment introduces high-density nanoprecipitates, featuring ultrafine parallel twin lamellae (∼2.4 nm), into the B2 matrix. These nanotwinned (NT) precipitates, unprecedented in traditionally processed HEAs, form via an intriguing two-step process, involving the transformation of the hexagonal close-packed into an NT structure through the slipping of Shockley partial dislocations. The successful incorporation of nanotwin into precipitates delivers remarkable strengthening of 565 MPa without compromising ductility compared to the as-built sample. The resulting tensile strength reaches 2200 MPa at room temperature, marking one of the highest strengths reported for additively manufactured HEAs. This breakthrough paves the way to fabricate structural materials with unique microstructures and excellent properties for broad applications.