Size Effects on Process-Induced Porosity in Laser Powder-Bed Fusion Additive Manufacturing

Abstract The design freedom of laser powder-bed fusion (L-PBF) additive manufacturing makes it suitable for fabricating intricate parts like lattice structures with numerous thin struts. However, L-PBF fabricated thin struts show different morphological and mechanical characteristics compared to bulk-sized parts due to distinct scan lengths that result in different melt-pool behavior between transient and quasi-steady states. This study aims to understand the keyhole porosity characteristics of thin struts, fabricated by L-PBF, incorporating a range of strut sizes, also with various levels of linear energy densities. Micro-CT and image analysis were employed for porosity measurements and evaluations. The results generally show keyhole-porosity decreasing with the decrease of the energy density, though with varying patterns across the higher energy density range. Thus, keyhole porosity in struts is severe at high laser powers and low scan speeds. A major finding reveals that the porosity actually reduces with a decrease in the strut size, plausibly because the keyhole has not reached a stable state to induce permanent pore formation. This implies that a higher energy density, greater than commonly used in making bulk components, could be utilized in making small-scaled features to ensure not only full melting, but also with minimum keyhole porosity.