High strength Al0.7CoCrFeNi2.4 hypereutectic high entropy alloy fabricated by laser powder bed fusion via triple-nanoprecipitation

Abstract

Eutectic high-entropy alloys, composed of FCC/B2 phases with a narrow solidification interval and excellent fluidity, have become a new hotspot in additive manufacturing. Nevertheless, their microstructures exhibit significant sensitivity to processing parameters, feedstocks, and composition, ultimately limiting the alloys’ engineering applications. Here, a hypereutectic Al0.7CoCrFeNi2.4 alloy with a low cracking susceptibility index was designed by Thermo-Calc calculation and fabricated by laser powder bed fusion. Results show that the as-printed Al0.7CoCrFeNi2.4 alloy manifests a stable cellular structure, coupled with appreciable ultimate tensile strength (≥1200 MPa) and ductility (≥20%) over a wide range of processing parameters. After aging at 800 °C for 30 min, outstanding strength (1500 MPa) and elongation (15%) were obtained. Considerable mechanical properties after aging stem from a triple strengthening mechanism, i.e., L12 nanoprecipitates and rod-shaped B2 particles within the FCC matrix, along with Cr-enriched spherical nanoparticles in the B2 phase. Meanwhile, hierarchical structure, i.e., FCC dominated matrix, a discontinuous B2 phase, a precipitation-free zone in the B2 phase, and a K-S orientation relationship between FCC and B2, facilitate to maintain excellent plasticity. These results guide designing HEAs by AM with controllable microstructures and outstanding mechanical properties for industrial applications.