Abstract: The lack of fusion (LoF) pore defects, due to their directionally aligned nature, exert significantly different effects on the damage behavior of laser powder bed fusion (LPBF) components. This study employs ex-situ X-ray computed tomography (XCT) to investigate the impact of directionally aligned LoF pore defects on the mechanical properties and damage evolution in LPBF-fabricated IN718. A cross-scale high-fidelity finite element model is constructed by directly incorporating digital pore geometries extracted from each ex-situ XCT scan using the immersed boundary method, enabling accurate representation of complex internal pore defect structures without geometric simplification. The results reveal the dominant role of pore defect orientation, whether parallel (V-LoF) or perpendicular (H-LoF) to the loading direction, in controlling damage initiation and evolution, highlighting a heterogeneous regulatory mechanism governed by pore defect geometry configuration and spatial alignment. Furthermore, results indicate that the critical size threshold for deep-buried isolated LoF pore defects can reach 420 µm. V-LoF or H-LoF to the loading direction did not significantly weaken component strength but instead induced a potential strengthening effect. Notably, H-LoF pore defects exhibit a closure effect similar to V-LoF pore defects, yet increase matrix cracking propensity by 28 %. The original pore geometry configuration influenced crack propagation, causing deflection angles constrained within 0°-30° from the initial orientation. Additionally, a small-sized pore defect cluster (∼57 µm) with inter-pore defect spacing less than three times the largest pore dimension significantly accelerates material failure by inducing secondary crack networks (propagation rate ≥ 59 µm/%), exceeding the failure impact of typical LoF pore defects. These findings provide a theoretical foundation for performance evaluation and defect tolerance design in LPBF IN718 components.

Key words: L-PBF IN718, Lack of fusion pore defects, Damage evolution, X-ray computed tomography, Fracture mechanism