The microstructure and mechanical properties of the additive manufactured AlCoCrFeNi high entropy alloy

The equimolar AlCoCrFeNi high entropy alloy (HEA) was successfully fabricated by direct energy deposition (DED), and its phase composition, microstructure and mechanical properties were discussed systematically. The DED samples showed a duplex BCC crystal structure, which is consistent with the original powder state. The microstructure of the DED samples transferred from columnar grain structure into equiaxed dendritic structure along building direction from bottom to top. What's more, the crystallographic orientation in different positions of the DED samples showed an apparent difference. The columnar grain structure presented a strong texture in building direction at the bottom, while equiaxed dendritic structure exhibited random crystallographic orien-tations at the top. The equiaxed dendrites structure in the DED samples is comprised of dendrites (DR) and interdendrites (ID) regions due to elemental segregation. Meanwhile, the fine microstructure of DR and ID re-gions is discovered to be nano-sized spherical precipitates morphology and weave-like morphology, respectively. Furthermore, compared with AlCoCrFeNi HEA produced by conventional casting method, the mechanical properties of the DED samples display a superior combination of strength and ductility. Therefore, this research could provide an effective theoretical guidance for the preparation of high strength-ductility of HEAs.