In-situ TEM observation of -axis extension twin formation at grain boundaries

Effect of grain boundaries on {$10\overline{1}2$} twin formation and its mechanical response in Mg is investigated through in-situ TEM compression test. Compression direction is set to be normal to the <c>-axis, which is a favorable orientation to form {$10\overline{1}2$} twins. In case of a single crystal, $\left\{10\bar{1}2\right\}$ twins form in the vicinity of the contact region of compression-tip with the specimen, as reported in previous studies. On the contrary, when the specimen has a grain boundary, this interfacial defect becomes the nucleation/formation site for twins. Stress required to form the twins is lower than that in a single crystal. Grain boundaries, which have a role in prevention of dislocation slips, create high stress fields; as a result, they lead to nucleation of a twin embryo. While twin nucleation is a probabilistic event, stress required to form the twins shows size effect.