Reversion of a Parent {130}⟨310⟩α′′ Martensitic Twinning System at the Origin of {332}⟨113⟩β Twins Observed in Metastable β Titanium Alloys

In bcc metastable β titanium alloys, and particularly in superelastic alloys, a unique {332}⟨113⟩ twinning system occurs during plastic deformation. However, in situ synchrotron x-ray diffraction during a tensile test shows that the β phase totally transforms into α" martensite under stress in a Ti-27Nb (at. %) alloy. {332} β twins are thus not formed directly in the β phase but are the result of the reversion of {130} α'' parent twins occurring in martensite under stress. The formation of an interfacial twin boundary ω phase is also observed to accommodate strains induced during the phase reversion.