Grain boundary shear–migration coupling—I. In situ TEM straining experiments in Al polycrystals

Grain boundary (GB) migration was dynamically observed and characterized by means of in situ transmission electron microscopy straining experiments at moderate temperature in ultrafine grain aluminium. This motion is a response to the applied external stress, which leads to faceted fast growth of some grains at the expense of smaller ones. The combined use of fiducial markers and image correlation made possible a measure of strain associated with GB migration. The crystallographic orientation of both sides of moving GB was simultaneously recorded. The shear produced by the observed migration was thus estimated, leading to a coupling factor close to 20%. These results are discussed and compared with existing models describing the coupling between shear stress and GB migration.