On the existence of transformation-induced antiphase boundaries in the γ-phase of two-phase TiAl-based alloys

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Abstract
The existence of transformation-induced γ antiphase boundaries (APBs) is discussed in TiAl-based alloys in which two phases, γ and α2, are in equilibrium at low temperatures. While such APBs are frequently observed in the metastable γ-phase after the massive transformation α → γ, they are rarely observed within the γ lamellae of the so-called lamellar structure. In both cases (massively transformed structure and lamellar structure), however, other possible transformation-induced defects, such as twin and pseudo-twin boundaries as well as order-related domain boundaries, are found in abundance in the γ-phase (ordered tetragonal L10). The possibility of coupling of APBs with the other boundaries is examined in order to explain the above-mentioned experimentally observed difference regarding the γ APBs.