The yield strengths of Ti-45Al-xNb and Ti-49Al-xNb (x = 0, 10) with nearly equiaxed γ microstructures were measured at 900C. The addition of Nb was found to increase the yield strength, but variations in Al content had little effect upon the yield strength of binary TiAl alloys. In order to understand the strengthening effect of Nb, stacking-fault energies were measured by using weak-beam transmission electron microscope techniques. It was found that the self-interstitial stacking-fault energy decreased significantly with decreasing Al content of the γ-phase in binary alloys, but was essentially independent of the Al content in ternary alloys.

Effect of Al Content and Nb Additions on the Strength and Fault Energy of TiAl Alloys. W.J.Zhang, F.Appel: Materials Science and Engineering A, 2002, 329-331, 649-52