Cross-slip and glide behavior of ordinary dislocations in single crystal gamma-Ti-56Al

Single crystals of Ti-56A1 deformed at 873 K in [1 6 3] and [1 12 5] orient ations exhibit anomalous hardening. The anomalous hardening increases with increasing the Schmid factor for cross-slip in (1 1 0) plane as well as a ( 1 1 1) cross-slip plane. The yield stress and CRSS show temperature depende nce as well as orientation dependence. The deformation structure of these c rystals was observed by TEM. The TEM study shows that ordinary dislocations of screw character were the main deformation structure, but these dislocat ions were frequently pinned by "superjogs" in (1 1 0) planes. The alloy wit h a higher flow stress shows a wide spread presence of the (1 1 0) edge dis location segments. These edge segments appear to have formed through a doub le cross-slip mechanism in which a screw dislocation cross-slipped onto (1 1 0)plane from the (1 1 1) primary slip plane and subsequently cross-slip a gain onto a (1 1 1) plane. This double cross-slip leaves a pair of short ed ge segments "superjogs" in (1 1 0) plane. It appears that these superjogs a re immobile in the forward direction, but mobile in the lateral directions. As a result, these (1 1 0) superjogs act as pinning points, but also, prov ide a Frank-Read source for formation of dislocation loops as well as dislo cation dipoles. These loops and dipoles probably contribute to alloy harden ing at high temperatures. (C) 1999 Elsevier Science Ltd. All rights reserve d.