Controlling microstructural and mechanical properties of direct laser deposited Inconel 718 via laser power

The control of grain structure, texture and micro-segregation during additive manufacturing is important due to their impact on the mechanical properties. In this work, multiple single walls were deposited using Inconel 718 powder by the Direct Laser Deposition (DLD) process. The influence of a wide range of laser power (150–1900 W), as well as the thermal gradient, were characterized using electron microscopy and hardness testing. The heat input effect on the microstructural, dendritic morphology, and microhardness was also examined. The results illustrated that a higher thermal gradient due to lower heat input tends to form equiaxed grains and more Nb-segregation, whilst a higher heat input develops columnar grains with low Nb-segregation. The segregations within the interdendritic boundaries increased in size when the heat input was increased, whilst the contribution from precipitation strengthening was not significantly evident in the as-fabricated condition. A wall with two different powers was also deposited to demonstrate the possibility of creating functionally graded structures through the control of laser power.