Mechanism of Very‐High‐Cycle Fatigue Crack Behavior in Gradient Bimodal Structure of Hastelloy C‐276

Understanding small‐crack behavior in Hastelloy C‐276 is essential for very‐high‐cycle fatigue (VHCF) studies, as crack growth strongly depends on microstructural features and deformation modes. This research explores the influence of gradient bimodal grain structures and slip bands on VHCF‐induced damage in Hastelloy C‐276. The findings show that fatigue cracks typically nucleate on favorably oriented slip planes within coarse grains, with primary activity occurring on the {1 1 1} slip planes. Because a single‐slip system cannot accommodate the deformation, multiple‐slip systems are activated, deflecting short cracks and slowing their propagation. Notably, the gradient distribution of coarse and fine grains enhances the fatigue resistance of the alloy.