Effects of annealing on the structure and mechanical properties of FeCoCrNi high-entropy alloy fabricated via selective laser melting

To widen the applications of FeCoCrNi high-entropy alloys (HEAs) fabricated via selective laser melting, their mechanical properties must be improved, and annealing plays an important role in this regard. In this study, the microstructure, residual stress, and mechanical properties of the as-printed specimen and specimens annealed at 773-1573 K for 2 h were compared. As the annealing temperature increased, the specimen structure recrystallized from all columnar grains to equiaxial grains containing numerous annealing twins. The dislocation network, which formed during the solidification process under considerable shrinkage strain, decomposed into dislocations. The residual stress, yield strength, and hardness decreased, while the plasticity and impact toughness increased. During the deformation of as-printed and low-temperature-annealed specimens, the dislocation network remained unchanged and provided resistance to the dislocations moving within it, thus strengthening the specimen. The tensile strength remained largely unchanged owing to the reduction in the residual stress during low-temperature annealing, as well as the formation of the twinning network and dislocation wall under large deformation upon high-temperature annealing. Meanwhile, the ductility greatly increased, thus increasing the potential for industrial application of HEAs.