CRYSTALLOGRAPHIC ASPECTS OF DEFORMATION TWINNING AND CONSEQUENCES FOR PLASTIC DEFORMATION PROCESSES IN γ-TiAi

摘要

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 Ll_0 structure of the γ-phase and quantifies the resulting deformation for differ- ent crystallographic directions. In addition, the open question is addressed whether twin interfaces rep- resent 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 dislo- cation plasticity. The impact of this effect on ductility depends on the volume fraction of twins.