Critical damage events of 3D printed AlSi10Mg alloy via in situ synchrotron X-ray tomography

Fish-scale-like melt pool structures and internal defects are characteristic features in additively manufactured (AM) metals. These play a critical role in the damage and fracture processes under different service loading conditions. However, the relationship between these damage features and loading conditions, as well as the spatial interactions between melt pool structures and internal defects remains poorly understood. Using in situ time-lapse synchrotron X-ray tomography and diffraction, we identify the initiation and growth events of lifelimiting damage under tensile, low cycle fatigue (LCF), and high cycle fatigue (HCF) loading. A novel transition from meso-structure insensitive, defect-dominated short fatigue crack propagation to a meso-structure sensitive mechanism occurs as the plastic zone expands ahead of a growing crack from HCF to LCF to tensile loading. Under tension and LCF, the damage accumulation gradually increases and micro-voids nucleate at the melt pool boundaries (MPBs) after which the crack path follows the MPBs. In contrast, under HCF, surface defects initiate fatigue cracking and the MPBs have a very limited effect on the crack propagation path. Finally, a physics-informed machine learning method is introduced to develop a novel methodology for predicting fatigue life by including three-dimensional features of defects in AM parts.