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.