Grain Rotation and Crack Propagation in Bulge-Tested Gold Films with 4D-STEM

Abstract

This work investigates the stable crack propagation in notched, ultrafine-grained, freestanding Au films under cyclic loading with a bulge tester. Using intermittent transmission electron microscopy, including 4D scanning transmission electron microscopy, the study investigates dislocation activities and grain-boundary-mediated processes during crack propagation at nanoscale resolution. The regions surrounding the propagating crack show significant out-of-plane grain rotation, grain boundary migration, and grain growth and coalescence. Orientation mapping highlighted the influence of grain orientations and misorientations on deformation localization and the crack propagation path, emphasizing the complex interplay of microstructural features in fatigue properties. The findings highlight the role of grain-boundary-mediated mechanisms in the cyclic fatigue of metallic thin films, providing insights into damage mechanisms at the nanoscale.