It was recalled that the characterization of ½<112] super-dislocations in the γ-phase led to the observation of an asymmetrical or abnormal contrast during transmission electron microscopy. The diffraction contrast from the core of these super-dislocations did not always obey the rules of diffraction contrast which had been established for analyzing partial dislocations that bounded stacking faults. In particular, a configuration involving 3 similar Shockley partials on adjacent planes had often been ruled out due to the absence of fringes which would indicate the presence of stacking faults. In order to determine the dissociated configuration, weak-beam transmission electron microscopic observations of edge-oriented ½<112] super-dislocations were correlated with computer-simulated images. The dissociation of these super-dislocations into similar 1/6<112] Shockley partial dislocations which bounded a superlattice extrinsic and intrinsic stacking-fault pair was then deduced from the analysis. A comparison of experimental and simulated images confirmed that the formation of an antiphase boundary or complex stacking fault-linked dissociation, or locking by stair-rod dislocations, could be ruled out.

Weak-Beam Analysis of Dissociated ½<112] Superdislocations in γ-TiAl. M.Kumar, S.Sriram, A.J.Schwartz, V.K.Vasudevan: Philosophical Magazine Letters, 1999, 79[6], 315-25