Formation of {112¯2} contraction twins in titanium through reversible martensitic phase transformation

Abstract We report the discovery of a non-conventional { 11 2 ¯ 2 } twinning mechanism in α -titanium through reversible α → ω → α martensitic phase transformations. Specifically, the parent α -phase first transforms into an intermediate ω -phase, which then quickly transforms into a twin α -phase, leading to the formation of { 11 2 ¯ 2 } contraction twins. In addition, we prove that the reversible α → ω → α phase transformations follow strict orientation relations between the parent α -, intermediate ω -, and twin α -phases. Finally, we demonstrate that our mechanism agrees with classical twinning theory in the shuffle, shear, and conjugate twinning plane. This study reveals the important role of the intermediate ω -phase in the twinning process, adding critical details to the existing mechanism of { 11 2 ¯ 2 } twinning.