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 cryst al Ti-56Al show orientation-dependent deformation in addition to the temper ature dependence. The orientation dependent deformation of the CRSS under s ingle slip of ordinary dislocations at high temperatures was found to be as sociated with cross-slip in {110) planes. The activation energy of the cros s-slip was found to be 0.45 eV. Similar temperature and orientation depende nce of the CRSS in single slip of < 101] superdislocations occurs by two di fferent 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) c ross-slip. In the temperature-change experiments of yield stress, the ordin ary slip showed thermal irreversibility while < 101] superdislocations exhi bited partial reversibility. Such irreversibility appears to be associated with the temperature dependence of cross-slip mode. (C) 2000 Elsevier Scien ce Ltd. All rights reserved.