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 consisti ng of primary equiaxed gamma -grains and lamellar alpha (2) + gamma colonie s after creep deformation at elevated temperatures (650-750 degreesC) was s tudied by transmission electron microscopy (TEM). In both primary gamma -gr ains and gamma -laths within lamellar alpha (2) + gamma colonies, ordinary 1/2[110] dislocations were observed and superdislocations could seldom be f ound. Both true twins created by 1/6[112] partial dislocations and pseudotw ins created by 1/6[121] partial dislocations were observed in the primary g amma -grains, while planar stacking faults were more common in gamma -laths . A detailed contrast analysis by TEM showed that the planar stacking fault s 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 stoichiom etric binary TiAl alloys. The observed deformation substructure is compared and contrasted with that of binary TiAl alloys. (C) 2001 Elsevier Science B.V. All rights reserved.