Investigation of Geometry, Microstructure and Defect Formation in Layers Fabricated in LPBF-Processed Inconel 738LC Alloy

Laser powder bed fusion (LPBF) stands at the forefront of additive manufacturing, enabling the creation of complex metal components with unprecedented precision. Despite its potential, defects in single-passes and single-layers often arise from suboptimal process parameters like laser power, scan speed, overlap rate, and layer thickness. This study presents a systematic integration approach for optimizing LPBF processing of Inconel 738LC, a challenging high-performance nickel-based superalloy. By combining single-pass geometric optimization with single-layer fabrication analysis, the research establishes correlations between processing parameters, microstructural evolution, and defect formation mechanisms. Experimental results reveal how varying areal energy density (AED) influences molten pool behavior and microstructural characteristics in layers. At an AED of 3.81 J/mm², the microstructure in overlap regions suggests equiaxed and columnar dendritic growth patterns. At an AED of 6.31 J/mm², the microstructure appears to exhibit equiaxed and cellular growth characteristics. The study identifies that defects such as shrinkage porosity, cracks, lack-of-fusion, and gas porosity are associated with the lowest AED values, while higher AED values result in improved layer quality. This integrated methodology provides practical guidelines for parameter optimization in LPBF processing of IN738LC, contributing to the advancement of defect-free fabrication strategies for this notoriously difficult-to-process superalloy.