Strategies to Mitigate Interlayer Porosity in the Laser-Directed Energy Deposition Process

Abstract

Abstract. Laser-directed energy deposition (L-DED) offers unique advantages for fabricating large-scale metallic components and repairing high-value parts. However, recurring interlayer porosity, particularly while depositing targeted geometry and dimensions, remains a major limitation affecting structural integrity. In this study, systematic deposition strategies were developed to mitigate interlayer porosity by controlling track overlap and optimizing energy apportionment, the two aspects that have not been reported together in previous L-DED studies. Experimental analysis showed that increasing the percentage overlap from 30% to 40% significantly reduced porosity, whereas defining the overlap based on the full width at half maximum (FWHM) provided a more geometry-representative approach. A 30% FWHM overlap was found to be most effective in disrupting periodic porosity recurrence. Additionally, introducing skewed track alignment minimized valley-to-valley overlap across layers, further reducing defect formation. Complementary to geometric strategies, interlayer laser polishing with circular and line beams facilitated pore closure while refining the interlayer microstructure. A key novelty of this work lies in coupling overlap optimization with energy apportionment between powder and substrate, achieved by adjusting the stand-off distance (SoD), which is quantified by a unique experimental approach. This enhanced molten pool flow and ensured improved remelting of the previously deposited layer, which, when combined with a 30% FWHM overlap, effectively eliminated visible interlayer porosity, validated by micro-computed tomography analysis. The integrated approach of optimized overlap, energy apportionment, and interlayer polishing enabled defect-free fabrication of straight walls as well as complex turbine blade profiles, while simultaneously enhancing strength and ductility.