Asymmetric pore distribution in PBF-LB/M In718 thin-walled structures: Contour morphology and welding quality

Abstract

Current research on In718 alloys produced by powder bed fusion-laser beam metals (PBF-LB/M) is mainly focused on the deformation challenges, while porosity has received less attention. This study focused on the porosity of the sub-surface of printed components, which is influenced by thickness, and the need to optimize the contour space to improve the print quality of thin-walled structures. The results illustrated that when the contour space was bigger than 0.04 mm, an asymmetry of contour melt tracks inevitably appeared for thin-walled structures, regardless of the placement angle. It was also found that asymmetric contour melt tracks were caused by the asymmetric hump effect of internal melt tracks. A localized collapse of one side of the internal melt tracks can cause breakage of the contour melt tracks. This is due to the lack of liquid metal at that location during contour melt track formation. Meanwhile, the contour melt track on the opposite side remains mostly undamaged. These broken contour melt tracks could cause asymmetric pore defects during the deposition process. Computational Fluid Dynamics (CFD) simulations were used to validate the contour scanning process. The results showed that a 0.04 mm contour space could significantly reduce the one-sided hump of the internal melt tracks and form a plump contour melt track, which would reduce the problem of local overthickness in the subsequent powder layer during powder spreading processes, thereby reducing the lack of fusion. This research provided valuable theoretical insights and practical guidance for optimizing the PBF-LB/M process for thin-walled In718 parts, with significant implications for engineering applications and academic innovation.