ON THE EXISTENCE OF TRANSFORMATION-INDUCED ANTIPHASE BOUNDARIES IN THE GAMMA-PHASE OF 2-PHASE TIAL-BASED ALLOYS

The existence of transformation-induced gamma antiphase boundaries (APBs) is discussed in TiAl-based alloys in which two phases, gamma and alpha2, are in equilibrium at low temperatures. While such APBs are frequently observed in the metastable gamma-phase after the massive transformation alpha-->gamma, they are rarely observed within the gamma 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 gamma-phase (ordered tetragonal L1(0)). The possibility of coupling of APBs with the other boundaries is examined in order to explain the above-mentioned experimentally observed difference regarding the gamma APBs.