Abstract: In the present paper, the microstructures of the two-phase alloy specimens of Ti-48AlMn-Nb, deformed at room temperature, 700℃and 900℃,have been investigated by using an EM400T transmission electron microscope. For specimens deformed at room temperature it is observed that (1/2) [011] superdislocation, normal (1/2) [110] dislocations, stacking fault band and a few twins etc. formed mainly in r-phase and a (1/2) [011] superdislocation preferentially decomposes into two partial dislocations with an antiphase boundary between them, which makes the dislocation difficult to move. The normal (1/2) [110] dislocations move with a long dragging tail behind them and have a low mobility In addition, the existence of a few twins implies a low mobility of (1/6) <112> twin dislocations, which leads to low plasticity of the allow. For samples deformed above 700℃,(1/2) [110] dislocations are in majority in the r-phase and exhibit short and bending dislocation segments without dragging tails,which may have resulted from an increased mobility of (1/2) [110] dislocations due to thermal activation. Meanwhile, (1/2) [011]superdislocation disappears, the mobility of (1/6)<112> dislocations is greatly increased, and thus a lot of twins are produced in r-phase. These make the plasticity of the alloy notably enhanced. The laminated structures in the alloy may be transformed into stacking fault bands during deformation at room temperature and the deformation above 700℃leads to the generation of a great quantity of twins.

Key words: dislocation, stacking fault, twin, TiAl alloy