Analysis of process parameter variations and heat treatment effects on the microstructure and mechanical properties of Inconel 718 fabricated by laser powder directed energy deposition (LP-DED)

This study investigates the influence of laser power and subsequent heat treatments on the microstructure and mechanical properties of Inconel 718 specimens fabricated via Laser Powder Directed Energy Deposition (LP-DED). Five sets of samples, produced using laser power ranging from 350 W to 2620 W, were subjected to a standardized heat treatment process comprising stress relief, hot isostatic pressing (HIP), solution treatment, and two-step aging. The evolution of the microstructure at each heat treatment stage was characterized in correlation with hardness, tensile properties, and fatigue life. Results demonstrate that complete heat treatment homogenizes and refines the microstructure, transitioning from dendritic to an austenitic structure with annealing twins, leading to an increase in hardness. Additionally, despite variations in printing parameters, mechanical properties such as tensile strength and fatigue resistance remained consistent. This study reveals that specimens fabricated at 350 W exhibited the finest microstructure, yielding overall superior mechanical properties. These findings contribute to the optimization of post-processing methodologies for LP-DED-manufactured Inconel 718 components, particularly for aerospace applications.