Effect of Al content and Nb addition on the strength and fault energy of TiAl alloys

The yield strengths of Ti–45Al–xNb and Ti–49Al–xNb (x=0, 10) with a nearly-equiaxed gamma microstructure were measured at 900 °C. Nb addition was found to largely increase the yield strengths but the variation of Al content has little influence on the yield strength of binary TiAl alloys. To understand the strengthening effect of Nb, the stacking fault energies in these alloys were measured using weak-beam transmission electron microscope (TEM) techniques. The SISF energy decreases significantly with the decreasing of Al content of γ phase in binary alloys but is practically independent of the Al content in ternary alloys. The implications of the dissociation behavior on the mechanical properties of the material will be discussed.