Microstructure and Residual Stress Evolution of Laser Powder Bed Fused Inconel 718 under Heat Treatments

The current work aimed to study the influence of various heat treatments on the microstructure, hardness, and residual stresses of Inconel 718 processed by laser powder bed fusion process. The reduction in residual stresses is crucial to avoid the deformation of the component during its removal from the building platform. Among the different heat treatments, 800 degrees C kept almost unaltered the original microstructure, reducing the residual stresses. Heat treatments at 900, 980, and 1065 degrees C gradually triggered the melt pool and dendritic structures dissolution, drastically reducing the residual stresses. Heat treatments at 900 and 980 degrees C involved the formation of delta phases, whereas 1065 degrees C generated carbides. These heat treatments were also performed on components with narrow internal channels revealing that heat treatments up to 900 degrees C did not trigger sintering mechanisms allowing to remove the powder from the inner channels.