Direct observation of disconnection-mediated grain rotation

Grain rotation is a well-known phenomenon during plastic deformation and recrystallization of polycrystalline materials. Theoretical models suggest that atomic-scale processes of grain rotation commonly involve disconnection flow associated with grain boundary (GB) migration, but direct observations have been rare thus far. Here, we present direct evidences that grain rotation in polycrystals can proceed through the motion and annihilation of curved GB disconnections, using in situ nanomechanical testing and atomistic simulations. The dynamics of curved GB disconnections often accompanies an orientation change of grains in real polycrystals, by which the nanograin rotates gradually alongside GB migration and GB curving in three-dimensional (3D) space. This finding has implications for understanding GB-mediated processes in polycrystalline materials.