Plastic deformation behaviour and deformation substructure in Al-rich TiAl single crystals deformed at high temperatures

Plastic deformation behaviour in Ti-54.7 at.%Al and Ti-58.0 at.%Al single crystals was examined around and above the anomalous strengthening peak temperature (T-p) focusing on the effect of Al5Ti3 superstructure. The Al5Ti3 superstructure developed in the L1(0) matrix of Ti-58.0 at.%Al, and the size of the Al5Ti3 phase once increased during annealing at 800 degrees C and then decreased with increasing temperature, while no significant evidence of the Al5Ti3 particles was obtained in Ti-54.7 at.%Al from TEM observation although diffuse scattering corresponding to the spots for the Al5Ti3 superstructure was observed. The transition of slip plane for 1/2 < 110] ordinary dislocations from {111} to {110) and/or (001) occurred at and above T-p due to anisotropy of anti-phase boundary energies on {111}, {110) and (001) in the Al5Ti3 superstructure. Anomalous strengthening is related to the development of this superstructure which may assist the cross-slip of some parts of 1/2 < 110] ordinary dislocations onto {110) and/or (001) resulting in the formation of dragging points to the motion of the dislocations. (C) 2001 Elsevier Science Ltd. All rights reserved.