Origin of {112} < 111 > antitwinning in a Ti-24Nb-4Zr-8Sn superelastic single crystal

112 ⟨ 111 ⟩ β twins are observed in a superelastic β Ti-24Nb-4Zr-8Sn (wt.%) single crystal after tensile test. A careful Schmid factor analysis shows that these twins are formed in the antitwinning sense regarding the classical 112 ⟨ 111 ⟩ β twinning system of bcc structures. These are then 112 ⟨ 111 ⟩ β antitwins. Moreover, a full stress-induced martensitic (SIM) transformation of β phase into α" martensite is evidenced from in situ synchrotron X-ray diffraction. This transformation is fully accomplished before the onset of plastic deformation and, in turn, the formation of twins. From crystallographic reconstruction, 112 ⟨ 111 ⟩ β antitwins are shown to be passively formed from the reversion, during the reverse SIM transformation when the stress is released, of 110 110 α ″ twins actually formed in α" martensite. The martensitic transformation occurring before twinning plays a key role in the activation of antitwinning systems by reducing both shear and shuffle magnitudes of twinning. Variant selection of stress-induced martensite and Schmid factor analysis show that the classical 112 ⟨ 111 ⟩ β twins can never be activated in β titanium alloys involving SIM transformation, while the non-classical 112 ⟨ 111 ⟩ β twinning system in the antitwinning sense is always favored. Graphical abstract