Interaction of cracks with precipitates and grain boundaries: Understanding crack growth mechanisms through focused ion beam tomography

Focused ion beam tomography is a new powerful tool to investigate the three-dimensional (3-D) spreading of microcracks. In this study, the interaction between a fatigue microcrack with a grain boundary decorated by carbide precipitates in a directionally solidified Ni base alloy is investigated. The carbide precipitates strongly influence crack growth by initiating geometrically necessary steps in the crack plane. 3-D reconstruction shows that the sub-surface orientation of grain boundaries is an important factor for interpreting crack growth rate at the surface.