Selective laser melting of an equiatomic CoCrFeMnNi high-entropy alloy: Processability, non-equilibrium microstructure and mechanical property

The selective laser melting (SLM) of an equiatomic CoCrFeMnNi high-entropy alloy (HEA) powder was studied, with emphasis on its non-equilibrium microstructural evolution and mechanical properties. The printed sample density increases gradually with increasing laser energy density and then decreases at an over-high laser energy density. The microstructure of SLM printed HEA exhibits a large number dislocation pile-ups and lattice distortion. Of particular intrigue are the existence of nanotwins and tetragonal σ phase in SLM printed HEA; such nanotwins and σ phase have never been observed in either cast or deformed HEA with true strain below 3.7%. The grain refinement by rapid solidification and σ phase synergistically improve the mechanical properties, as compared with conventionally solidified HEA. Hot isostatic pressing (HIP) was performed to improve the densification, yielding the increase of tensile strength from 601 MPa of SLM printed sample to 649 MPa after HIP.