Crystallographic aspects of deformation twinning and consequences for plastic deformation processes in γ-TiAl

Abstract Mechanical twinning is an important deformation mechanism in the γ-phase of near-γ-TiAl alloys at room temperature as well as at high temperature. The present work examines the crystallography of twinning in the ordered L10 structure of the γ-phase and quantifies the resulting deformation for different crystallographic directions. In addition, the open question is addressed whether twin interfaces represent obstacles for glide dislocations. It is shown that one part of the possible glide dislocations remains completely unaffected by the twin interface because their Burgers vectors lie in the twin plane. The other part of the dislocations has to change its glide directions while passing the interface, which can occur by suitable dissociation processes. Prerequisite is a sufficiently high applied stress. The reoriented twin may be more favorably oriented for some glide directions than its parent crystal and thus promote further dislocation plasticity. The impact of this effect on ductility depends on the volume fraction of twins.