Slip responses and pre-twin structure evolution based on indentation pile-up in magnesium single crystal

Slip behavior and microstructure evolution caused by the indentation pile-up deformation were studied in Mg single crystal with {10–12} pre-twin structure at room temperature. The anomalous indentation is formed on the surface of the large-size single crystal. It is attributed to plastic flow induced by the combined effects of dislocation slip, detwinning and {10–12} twinning during indentation. At the early stage of indentation, basal slip dominates the pile-up deformation. And the reaction structure of basal slips, i.e. (0001) slip plane in the twin to correspond to (0001) slip plane in the matrix, is frequently formed on the twin boundary in order to facilitate plastic relaxation of the local stress on the twin boundary. Under pile-up pattern, the stress state favors detwinning. And detwinning behavior is subjected to effects of stress-field magnitude and pre-twin size. For the little-volume and large-volume pre-twins, detwinning behaviors play the modes of twin shrinkage and “local detwinning” respectively. The latter might involve reverse nucleation and growth of matrix. Although pile-up pattern is unfavorable to {10–12} twinning, stress concentration caused by the interaction between slip dislocations and twin boundary induces the local twin growth on the interface. In addition, a pyramidal slip is found in matrix, and its slip trace is corresponding to (0001) slip trace in twin.