Microstructural characterisation of defect structures in a TiAl-base Ti–47Al–2Nb–2Mn(at.%)+0.8vol.%TiB2 alloy

The microstructure of a Ti–47Al–2Nb–2Mn(at.%)+0.8vol.%TiB2 alloy consisting of primary equiaxed γ-grains and lamellar α2+γ colonies after creep deformation at elevated temperatures (650–750°C) was studied by transmission electron microscopy (TEM). In both primary γ-grains and γ-laths within lamellar α2+γ colonies, ordinary 1/2〈110] dislocations were observed and superdislocations could seldom be found. Both true twins created by 1/6〈112] partial dislocations and pseudotwins created by 1/6〈121] partial dislocations were observed in the primary γ-grains, while planar stacking faults were more common in γ-laths. A detailed contrast analysis by TEM showed that the planar stacking faults lying on {111} planes are bound by all the f.c.c. variants of the 1/6〈121〉 Shockley partial dislocations in contrast to earlier results on stoichiometric binary TiAl alloys. The observed deformation substructure is compared and contrasted with that of binary TiAl alloys.