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 and twinning modes were recently discovered by Ostapovets et al. [Philos. Mag. (2017), 97, 1088–1101] and interpreted as – 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.