A Review of Emerging Metallic System for High-Energy Beam Additive Manufacturing: Al-Co-Cr-Fe-Ni High Entropy Alloys

Al-Co-Cr-Fe-Ni high entropy alloy (HEA) system is a newly developed category of metallic materials possessing unique microstructure, mechanical and functional properties, which presents many promising industrial applications. In recent years, additive manufacturing technology has given rise to a great potential for fabricating HEA parts of ultra-fine grains and geometrical complexity, thereby attracting great interest of researchers. Herein, a comprehensive review emphasizes on the recent developments in high-energy beam additive manufacturing of Al-Co-Cr-Fe-Ni HEA, in the aspects of their printing processes, microstructures, properties, defects, and post treatments. The technical characteristics of three typical high-energy beam additive manufacturing technologies for printing HEA, namely, selective laser melting (SLM), selective electron beam melting (SEBM), and directed energy deposition (DED) are systematically summarized. Typical crystal structure, grain, microstructure, as well as corresponding properties of Al-Co-Cr-Fe-Ni HEA manufactured by those technologies are primarily presented and discussed. It also elaborates the formation mechanisms of harmful defects related to the rapid solidification and complex thermal cycle during high-energy beam additive manufacturing. Furthermore, several kinds of post treatments with an aim to improve performance of HEA are illustrated. Finally, future research directions for HEA by additive manufacturing are outlined to tackle current challenges and accelerate their applications in industrial fields.