Influence of Process Parameters and Post-Processing Routes on the Densification, Surface Integrity, and Phase Evolution of L-PBF Inconel 718

Inconel 718 (IN718) is widely used in aerospace manufacturing due to its high-temperature strength and corrosion resistance, yet its performance in Laser Powder Bed Fusion (L-PBF) is often limited by porosity, lack-of-fusion defects, and heterogeneous microstructures arising from the rapid and localized melting of the process. This study investigates the effect of L-PBF process parameters, including laser power (100-200 W), scanning speed (900-1500 mm/s), and hatch distance (50-90 µm), and subsequent post-treatment routes, including Hot Isostatic Pressing (HIP) and a combined HIP + solution treatment followed by aging, on IN718. Analysis of 27 different samples, spanning volumetric energy densities (VEDs) between 37 and 222.2 J/mm³, revealed a clear densification threshold at 67 J/mm³. Below this limit, lack-of-fusion (LOF) defects caused the relative densities to fall below 94%, as confirmed by X-ray computed tomography (XCT). Surface roughness was predominantly governed by laser power, with Ra ranging from 1.272 to 18.519 µm. Microstructural characterization by SEM and OM revealed that while the as-built state suffered from characteristic dendritic segregation, the HIP + HT route promoted full recrystallization and the secondary precipitation of strengthening γ″ and γ′ phases. Nanoindentation confirmed this evolution, showing a significant increase in both hardness and elastic modulus of post-treatment samples, attributed to the simultaneous closure of residual porosity and the dissolution of brittle Laves phases. These findings provide a quantitative framework for improving as-built surface quality with optimized bulk mechanical performance in additively manufactured superalloys.