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 L1₀ matrix of Ti–58.0at.%Al, and the size of the Al₅Ti₃ phase once increased during annealing at 8008C and then decreased withincreasing 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 ½<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 ½<110] ordinary dislocations onto {110) and/or (001) resulting in the formation of dragging points to the motion of the dislocations.