High strength and ductility eutectic high entropy alloy with unique core-shell structure

The as-printed AlCoCrFeNi2.1 eutectic high entropy alloys (EHEAs) alloys were manufactured from pre-alloy powders by selective laser melting (SLM) technology. The microstructure, mechanical properties and unique FCC-B2 core-shell structures of as-printed alloys were examined in detail. There are no obvious cracks, pores or defects found in as-printed alloys, and the highest relative density is more than 99.5%, showing an excellent metallurgical combination between contiguous melted layers. The as-printed alloys are consisted of FCC and B2 phases, presenting typical fish scale structures, which contain ultra-fine cellular and columnar structures, and exhibiting preferred orientation. Meanwhile, the ultimate tensile strength and elongation of the as-printed alloy manufactured by the optimum parameters are 1159.4 MPa and 29.0%, respectively. It is believed that the ultrafine grains and unique FCC-B2 core-shell structures formed during the SLM should be responsible for such outstanding mechanical properties. In addition, the edge dislocations at the interface formed due to thermal stress are observed, while the dislocation motion has been hindered by the unique FCC-B2 core-shell structures, thereby achieving a positive combination between ductility and strength. A certain theoretical analysis value and experimental references have been provided in this work for the further application of EHEAs in additive manufacturing.