Microscale investigations on additively manufactured Inconel 718: influence of volumetric energy density on microstructure, texture evolution, defects control and residual stress

In the present work, Inconel 718 (IN718) blocks were fabricated for initial screening using a wide range of volumetric energy density (VED) varying between 29 and 177 J/mm(3) within the machine specifications. The VED ranges from 66 to 111 J/mm(3) revealed to have maximum relative density (RD), i.e., above 99% with a minimum fractional porosity between 0.01% and 0.08%. Higher VED in the range from 128 to 177 J/mm(3) exhibited significant layer delamination. Based on the initial screening results, the samples were further fabricated within the identified process window of VED ranging between 38 and 111 J/mm(3) to ensure repeatability and to analyze the microstructural changes and residual stress (RS) formation. The as-fabricated microstructures exhibited columnar growth of grains along the build direction with varying Nb Wt.% between dendritic and interdendritic regions. The Nb segregation in the interdendritic regions was found to decreased by 17.09% while increasing the VED. The results showed that increasing VED changes the shape of the melt pool boundaries from shallow to deeper. Electron Backscatter Diffraction (EBSD) results showed the evolution of a strong texture in direction with an increase in grain size from 14.77 to 63 mu m as the VED increased. The tensile RS magnitude was found to be increased as the VED increased due to the high thermal gradient. The main challenge in the L-PBF process is the simultaneous control of defects, microstructure, texture, and RS formation. The findings of current research deliver a better VED window to fabricate defect less IN718 parts for aerospace applications.