Extensive twinning, glide and climb of ordinary dislocations and activity of <011] and ½<112] super-dislocations were observed in the γ phase of Ti-45Al-10Nb alloy after deformation at 900C using a strain-rate of 5 x 10-4/s. The presence of a moderate density of super-dislocations was likely to arise from high Nb-alloying of the γ phase. Two marked effects of high-Nb alloying of the γ phase were identified: an increase in the critical resolved shear stress for ordinary slip, and a decrease in the stacking-fault energy, as a result of Nb solid-solution and/or low Al concentrations in high-Nb alloyed γ phase. The critical resolved shear stress and the stacking-fault energy were estimated to be of the order of 180MPa and 20mJ/mm2, respectively. The high critical resolved shear stress and the difficulty of dislocation climb due to a low stacking-fault energy were believed to be the major factors responsible for the enhanced high-temperature strength of Ti-45Al-10Nb alloy.

Deformation Mechanisms in a High-Nb Containing γ-TiAl Alloy at 900C. W.J.Zhang, Z.C.Liu, G.L.Chen, Y.W.Kim: Materials Science and Engineering A, 1999, 271[1-2], 416-23