Deformation characteristics and dislocation structures in single phase gamma titanium aluminides

The yield stress curves of gamma Ti–Al alloys exhibit three characteristic regimes: normal behavior below RT; anomalous hardening above RT up to 1073 K; and softening above 1073 K. Furthermore, the CRSS curves of single crystal Ti–56Al show orientation-dependent deformation in addition to the temperature dependence. The orientation dependent deformation of the CRSS under single slip of ordinary dislocations at high temperatures was found to be associated with cross-slip in {110) planes. The activation energy of the cross-slip was found to be 0.45 eV. Similar temperature and orientation dependence of the CRSS in single slip of <101] superdislocations occurs by two different processes, each of which at the different temperature range. The one occurring at the low temperature range is associated with {111} cross-slip while the other at the high temperature range is identifiable with (010) cross-slip. In the temperature-change experiments of yield stress, the ordinary slip showed thermal irreversibility while <101] superdislocations exhibited partial reversibility. Such irreversibility appears to be associated with the temperature dependence of cross-slip mode.