Melt pool overlap as a key tool for microstructure design in PBF-LB/M of a Ni-based superalloy: Empirical and analytical approaches

This work presents a streamlined and industrially scalable methodology to design and control the microstructure in Inconel 939 (IN939) components fabricated by laser powder bed fusion (PBF-LB/M). Through a combination of empirical and analytical approaches, we identify the melt pool overlap perpendicular to the scan direction (SD) and to the build direction (BD) as a key metric to predict the formation of either columnar grains with strong < 001 > //BD fiber textures or equiaxed, weakly oriented microstructures. We demonstrate that combinations of processing parameters (laser power, scan speed, hatch distance, scan track length) leading to overlaps below a critical threshold of 0.6 inhibit epitaxial growth, yielding equiaxed, weakly textured grains. Multitrack experiments are introduced as a high-throughput method to construct melt pool overlap maps for a broad range of processing conditions, enabling rapid empirical selection of scan parameters. Furthermore, we propose an analytical framework based on a modified Rosenthal equation and a reformulated normalized volumetric energy density (E_v*), incorporating scan geometry and material properties. A simple logarithmic regression linking E_v* to melt pool overlap allows for the prediction of suitable process windows beyond those directly tested. This combined methodology offers a practical pathway for microstructure-informed design in PBF-LB/M of high-performance Ni-based superalloys, facilitating microstructural control in engineering components with complex geometries.