| Abstract Scope |
Grains in polycrystalline materials can undergo nearly-rigid-body rotation, commonly observed during grain growth, recrystallization, and plastic deformation in nanocrystalline materials. Grain rotation plays a central role in polycrystal dynamics (e.g., changing grain growth kinetics) and constitutes a primary deformation mechanism in nanocrystalline solids and may dominate texture evolution. Despite decades of research, the dominant mechanisms underlying grain rotation remain enigmatic. In this talk, I present direct evidence that grain rotation occurs through the motion of disconnections (line defects with step and dislocation character) along GBs. State-of-the-art in situ four-dimensional scanning transmission electron microscopy (4D-STEM) observations reveal the statistical correlation between grain rotation and grain growth/shrinkage. This correlation arises from shear-coupled GB migration and further the motion of disconnections, as demonstrated by in situ high-angle annular dark field STEM observations and the atomistic-simulation-aided analysis. These findings provide novel, quantitative insights into the structural dynamics of nanocrystalline materials. |