The relaxation of stresses which were associated with extrinsic grain-boundary dislocations in singular Σ = 3{111}, in vicinal Σ = 11 {311} and in general Σ = 11 {332} grain boundaries was investigated by means of in situ transmission electron microscopy under weak-beam conditions. In a singular Σ = 3 {111} grain boundary, combination and annihilation reactions occurred between extrinsic and intrinsic dislocations when they initially intersected one other. These reactions yielded the parallelism of the 2 types of dislocation, which was the basic configuration for the operation of all proposed incorporation models. Further evolution, via decomposition of the extrinsic grain-boundary dislocations into glissile and sessile components which could move away, was observed only once; at a very high temperature. Rearrangement of all of the sessile dislocations (extrinsic and intrinsic) into a periodic network was not observed; even after maintaining the thin foil at 930C for a long time. In the case of vicinal Σ = 11 {311} grain boundaries, a continuous spreading of extrinsic grain-boundary dislocation contrast, which had previously been observed under transmission electron microscopic bright-field conditions, was proved to be a decomposition process. Due to the use of the weak-beam technique, the wide image of a relaxed extrinsic grain-boundary dislocation was resolved into a set of small segments which arose from interactions between the extrinsic grain-boundary dislocations and the intrinsic dislocations. After annealing the thin foil at homologous temperatures of up to 0.4, all of the grain-boundary dislocations had rearranged themselves into a quasi-periodic network. This indicated that equilibration was almost reached. In the case of general Σ = 11 {332} grain boundaries, no widening of the extrinsic grain-boundary dislocation contrast was ever associated with decomposition phenomena. No discrete product of extrinsic grain-boundary dislocation decomposition was ever observed by means of transmission electron microscopy; even under weak-beam conditions. The differences between the accommodation processes, as a function of grain-boundary type, were explained in terms of the atomic structure of the grain boundary.

in situ Transmission Electron Microscopy Study of the Dislocation Accommodation in [101] Tilt Grain Boundaries in Nickel Bicrystals. S.Poulat, B.Décamps, L.Priester: Philosophical Magazine A, 1999, 79[11], 2655-80