Deformation mechanisms in a high-Nb containing γ–TiAl alloy at 900°C

Extensive twinning, the glide and climb of ordinary dislocations, and much activity of 〈011] and 1/2〈112] superdislocations were observed in the γ phase of Ti–45Al–10Nb alloy after deformation at 900°C at a strain rate of 5×10−4 s−1. The presence of moderate density of superdislocations is likely to arise from a high-Nb alloying in γ phase. Two important effects of high-Nb alloying in γ phase were identified: the increase of the critical resolved shear stress (CRSS) for ordinary slip, and the decrease of the stacking-fault energy (SFE), as a result of Nb solid solution and/or low Al concentration in high-Nb alloying γ phase. The CRSS and the SFE were estimated approximately to be on the magnitude of 180 MPa and ∼20 mJ/mm2, respectively. The high CRSS and the difficulty of dislocation climb due to low SFE are believed to be the major factors responsible for the enhanced high-temperature strength retention of Ti–45Al–10Nb alloy.