A one-step mechanism for new twinning modes in magnesium and titanium alloys modelled by the obliquity correction of a (58°,a+ 2b) prototype stretch twin

The \{ 11{ 2}2\} and \{ 11{ 2}6\} twinning modes were recently discovered by Ostapovets et al. [Philos. Mag. (2017), 97, 1088-1101] and interpreted as \{ {10{ 1}2} \}-\{ {10{ 1}2} \} double twins formed by the simultaneous action of two twinning shears. Another interpretation is proposed here in which the two conjugate twinning modes result from a one-step mechanism based on a (58°, a + 2b) prototype stretch twin and differ from each other only by their obliquity correction. The results are also compared with the classical theory of twinning and with the Westlake-Rosenbaum model.