Abstract: Developing high-strength and ductile metallic parts with designable shapes is an unfading research topic for material science and engineering. As a revolutionary technology, additive manufacturing (AM) provides a new pathway for producing complex-shaped metallic parts with the possibility of in situ tailoring their microstructure. However, AM is not always ideally applicable for all metals and alloys. Eutectic high entropy alloys (EHEAs) contain both the advantages of the eutectic alloys and high entropy alloys (HEAs), and EHEAs show significant potential in AM due to their excellent mechanical properties and good fluidity. Herein, heterogeneous and ultra-fine eutectic lamellar microstructure with directional growth along the deposition direction (DD) was obtained by adjusting the process parameters of AM to improve the strength and ductility of EHEAs. Compared with the as-cast sample, the simultaneous increment in both strength and ductility is achieved by AM. Combination of strength and ductility of the AM sample tensile along the DD direction (yield strength σ_y=1115 MPa, ultimate tensile strength σ_UTS =1417 MPa, ultimate tensile strain ε_U=23 %) in this work was superior to most of the additive manufactured alloys and comparable to the thermomechanical-treated EHEAs with the best mechanical properties. The high strength and good ductility of the AM were mainly attributed to the ultra-fine lamellar nature and fully constrained soft and hard lamellar microstructure, which produces an obvious hetero-deformation induced (HDI) strengthening and high crack buffering effect during the deformation. This work provides a new possibility to achieve high strength and ductile complex-shaped metallic parts via designing directional lamellar eutectic structures by AM.

Key words: Eutectic high entropy alloys, Additive manufacturing, Directional lamellar, Mechanical properties, Hetero-deformation induced hardening