In order to shed light on the enormous dependence of the critical resolved shear stress for the prism slip of Ti3Al, upon antiphase domain size, the morphologies and configurations of dislocations in crystals with various antiphase domain sizes were examined by means of transmission electron microscopy. Contrary to previous models, the dislocation had a wavy or winding morphology; depending upon L, the average antiphase domain size. Also, unpaired dislocations were observed in the antiphase domain structure with an L which was smaller than about 100nm, whereas super-partial dislocation pairs were observed in coarser antiphase domain structures. Based upon these observations, a new model of dislocation motion in relatively coarse antiphase domains was proposed. The model relied upon a detailed theoretical investigation of the interaction of dislocations with differently oriented antiphase domain boundaries. The dislocations moved by bowing-out between antiphase domain boundaries that were inclined with respect to their Burgers vector, b, because dislocation motion was interfered with by antiphase domain boundaries inclined with respect to b. However, they could move easily through antiphase domain boundaries which were parallel to b. As this recalled the Orowan mechanism, the model was deemed Orowan-like. For relatively coarse antiphase domain structures, with L greater than about 100nm, the dependence of the critical resolved shear stress, upon the antiphase domain size derived from this model, agreed with that measured experimentally. A mechanism of uncoupling of super-partial dislocation pairs was suggested which considered dislocation motion that sheared antiphase domain boundaries which were inclined with respect to b.

Effects of Antiphase Domains on Dislocation Motion in Ti3Al Single Crystals Deformed by Prism Slip. Y.Koizumi, Y.Minamino, T.Nakano, Y.Umakoshi: Philosophical Magazine, 2008, 88[4], 465-88