Weak-beam transmission electron microscopy study of dislocation accommodation processes in nickel Sigma=3 grain boundaries

摘要

The first steps of the accommodation of extrinsic dislocations in Sigma = 3 grain boundaries have been observed in nickel bicrystals. Two types of reaction have been investigated in detail using the weak-beam technique in addition to conventional transmission electron microscopy analyses and the image-matching technique. In one case, the decomposition of a trapped lattice dislocation in two products, not visible in the bright-field condition, can be seen as the necessary step preceding the emission of one product dislocation into the neighbouring crystal. This means that dislocation transmission through a grain boundary, even Sigma = beta, is never a direct process. In the other case, a reaction between an extrinsic dislocation and an intrinsic dislocation having different line orientations could be analysed owing to the visualization of a small dislocation segment in the weak-beam condition. This reaction has been interpreted as the first step of incorporation of an extrinsic dislocation in the intrinsic network. [References: 31]