The first steps in the accommodation of extrinsic dislocations in = 3 grain boundaries were observed in bi-crystals. Two types of reaction were investigated in detail by using the weak-beam technique in addition to conventional transmission electron microscopic analysis and the image-matching techniques. In one case, the decomposition of a trapped lattice dislocation into 2 products, a process which was not visible under bright-field conditions, could be seen to be a necessary step which preceded the emission of one product dislocation into the neighboring crystal. This implied that dislocation transmission through a grain boundary was never a direct process. In the other case, the reaction between an extrinsic dislocation and an intrinsic dislocation having differing line orientations could be analyzed via the visualization of a small dislocation segment under weak-beam conditions. This reaction was interpreted as being the first step in the incorporation of an extrinsic dislocation into the intrinsic network.

Weak-Beam Transmission Electron Microscopy Study of Dislocation Accommodation Processes in Nickel Σ = 3 Grain Boundaries S.Poulat, B.Décamps, L.Priester: Philosophical Magazine A, 1998, 77[6], 1381-97