Removing basal-dissociated 〈c+a〉 dislocations by {101¯

Energetic contributions to deformation twinning in magnesium

“…A micromechanical model for the twin formation energy is developed in the same section, with the energy contribution arising from the change in character of the prior GB found to be significant. The I 1 stacking faults (SFs) that form inside the twin and the associated defect structures that bound them are also found to possibly make significant energy contributions, amplifying the conclusions of recent experimental [47,48] and numerical studies [49] that emphasized the role of I 1 SFs inside tension twins. These results suggest that both of these contributions should be included in any comprehensive energy-based twin nucleation model going forward.…”

“…A closer examination of the defect substructure inside the twin in figure 12 reveals that the point where a SF intersects the twin boundary almost invariably coincides with a corner of a BP or PB facet. Such SFs have also been observed experimentally in {1012} twins [47,48], and their possible origins and the character of their bounding defects have been studied in detail [49,64,65]. The bounding defect in the twin boundary is specifically known to have disconnection character; the Burgers vectors and the step heights of the disconnections in figure 12 are given in the conventional notation b ±µ/±κ used in interfacial defect theory [66].…”

“…Two other structures are labeled in figure 6 in addition to the twin-matrix boundaries. The first are I 1 SFs that change the stacking order of the basal planes to ABACA (or equivalently BABCB); recent high resolution electron microscopy (HREM) studies have verified the presence of such SFs inside {1012} twins [47,48,57]. The SFs usually extend from the twin boundary on one side to the GB on the other, with the intersection with the twin boundary frequently occurring at a junction between CTB and PB facets.…”

Microstructure and mechanical properties of a double-pass friction stir processed AZ31B magnesium alloy

“…Due to the large average grain size of 2P-FSP, the calculated σ GB values were lower, resulting in large errors in the calculated values. However, according to the Schmid factor distribution in Figure 13, the average Schmid factors of the two tests were 0.37 and 0.18, respectively, indicating that the base slip of 2P-FSP was hard to activate when subjected to plastic deformation [40,41]. Therefore, the extension twins generated during stretching interacted with the original dislocations in the grains to improve the strength and ductility of the material, which showed a better strength-ductility matching compared to 1P-FSP.…”