Effect of the Volume Energy Density and Heat Treatment on the Defect, Microstructure, and Hardness of L-PBF Inconel 625

In this article, we investigated the effect of the process parameters and heat treatment on the defect formation, microstructure, and hardness of Inconel 625 manufactured by the laser powder-bed fusion (L-PBF) process. Specimens were fabricated with various scan speeds, laser powers, and hatch spacing to give a range of volume energy density (VED) between 108 and 156 J/mm(3). SEM analysis was conducted to identify the effects of the VED on the various defects. A columnar-dendritic microstructure was found in all specimens. The effect of heat treatment on the microstructure, including grain growth, carbide precipitations, and phase transformation, was also studied. The results of this study show that VED has an influential effect on the formation of defects, such as lack of fusion porosity, keyhole, gas pores, and micro-cracks. The microstructure and hardness dependency of the L-PBF Inconel 625 material on the VED and heat treatment emphasizes the importance of the optimum selection of VED and post-processing in the L-PBF manufacturing procedure. Finally, the hardness of the heat-treated and as-built specimens was measured, and their variations with VED were specified.