Fragmentation of α₂ plates in a fully lamellar TiAl during creep

The fragmentation and spheroidization of a2 laths in a fully-lamellar TiAl alloy during creep were examined. Three possible mechanisms, Rayleigh's perturbation model, subgrain boundary groove mechanism and intersection of deformation twins with ex2 lamellae were presented and discussed. During creep deformation, the pile-up of interfacial dislocations leads to a change of planar interface, which, in turn, causes a difference in local chemical potential, and further results in the spheroidization of a2 lamellae. On the other hand, the deformation of the ot2 phase is expected to be induced by the high local stress concentration introduced by the pile up of interfacial dislocations. The dynamic recovery process may lead to the formation of subgrain boundaries in the a2 lamellae, which results in the spheroidization and termination of a2 lamellae with the aid of diffusion during creep. © 1999 Materials Research Society.