It was recalled that it was commonly observed that, in 2-phase TiAl-based binary alloys, deformation of the γ-phase occurred via ½<110]-type ordinary dislocation activity and twinning which was associated with 1/6<112]-type partials. The microstructure of the present alloy (Ti-47Al-2Mn-2at%Nb + 0.8vol%TiB2), which had a duplex microstructure that consisted of primary equiaxed γ grains and lamellar α2 + γ colonies, was studied by using transmission electron microscopy after deformation at high temperatures. Planar stacking faults were found in the γ laths. Detailed contrast analysis, using transmission electron microscopy, showed that these stacking faults lay on {111} planes and were bounded by all of the face-centered cubic variants of the Shockley partial dislocations of 1/6<121>-type. This contrasted with the results for stoichiometric binary TiAl alloys, where only 1/6<112]-type Shockley partials were associated with the true twins. It was suggested that the addition of ternary and quaternary elements, such as Mn and Nb, promoted other variants of face-centered cubic-like dissociation in the present alloy.

Observation of Planar Stacking Faults in a Ti-Rich Two-Phase Ti-Al Alloy after Deformation at Elevated Temperatures. S.H.Chen, D.Mukherji, G.Schumacher, G.Frohberg, R.P.Wahi: Philosophical Magazine Letters, 2000, 80[1], 19-26