It was found that ½<110] unit dislocations in deformed samples exhibited a unique morphology. This comprised numerous pinning-points along the dislocation line, aligned roughly along the screw dislocation direction, and bowed-out segments between the pinning-points. The 3-dimensional arrangement of these dislocations was characterized on the basis of weak-beam transmission electron microscopic observations of deformed binary 50 or 52at%Al alloys. The bowed segments glided on parallel {111} primary planes, and the pinning-points were jogs with heights that ranged up to a maximum of about 40nm. The sub-structure evolution was consistent with dislocation glide that involved frequent double cross-slip and consequent jog formation. The dislocations experienced a large glide resistance during forward (non-conservative) motion of the jogs. The pinning of unit dislocations, an intrinsic process in these alloys, was not related to the presence of interstitial-containing precipitates. The temperature-dependent increase in the linear pinning-point density was not very sensitive to the alloy composition. A flow-stress model was outlined which was based upon a single dislocation that experienced a spectrum of resisting forces which resulted from a range of jog heights. That is, the shorter jogs contributed to the glide resistance via friction, while the higher jogs contributed via a dipole-dragging mechanism. The estimates of the resisting forces due to these processes were shown to account reasonably well for the measured flow-stress.

The Geometry and Nature of Pinning Points of ½<110] Unit Dislocations in Binary TiAl Alloys S.Sriram, D.M.Dimiduk, P.M.Hazzledine, V.K.Vasudevan: Philosophical Magazine A, 1997, 76[5], 965-93