Ex-situ XCT tracking of keyhole pore evolution and induced damage mechanisms in L-PBF IN718 for mechanical testing

Keyhole pores are a prevalent defect in laser powder bed fusion (L-PBF) additive manufacturing. Although the formation mechanism of keyhole pores is well understood, research on their deformation under load and subsequent impact on component damage behavior remains lacking. In this study, the dynamic evolution of L-PBF IN718 components with keyhole pores under coaxial tensile load was tracked through ex-situ XCT mechanical testing. The digital models derived from XCT reconstructions were directly applied to high-fidelity structural mechanics simulations via the immersed boundary finite element method (IBFEM). The results indicate that keyhole pores induced significant stress concentrations, with the maximum von Mises stress around the pores exceeding 8 times the material's yield strength. Keyhole pores exhibited a negligible tendency for closure throughout the entire lifecycle of the component, with a mean sphericity up to 0.97 even after cracking. Furthermore, for L-PBF IN718 components with a minimum section thickness of 2 mm, keyhole pores buried deeper than 360 μm beneath the surface did not contribute to premature cracking. The uneven deformation caused by skewed pore distribution did not alter the priority of cracking locations in the components. Open keyhole pores, particularly those adjacent to other keyhole pores, served as the initial points of cracking. Additionally, the accumulation of keyhole pores with angles less than 50° (between the long axis of the pore and the loading direction) was identified as a significant precursor to cracking failure. This study enhances understanding of the mechanisms governing load-induced keyhole pore evolution and the associated damage behavior.