Contraste en M.E.T. à deux ondes d'une dislocation rectiligne parallele à la surface libre d'un cristal anisotrope

Abstract

The contrast of a straight dislocation has been studied by transmission electron microscopy within the framework of the two-beam dynamical theory, when the dislocation is parallel to the two free surfaces of an elastically anisotropic thin foil. For the intensity computations the elastic field is assumed to depend only on the proximity of the dislocation to the closest free surface, i.e. the material is considered as a semi-infinite medium with either a lower or an upper free surface according to the case. Typical simulated images of dislocations in a Cu-8 at.% Si alloy and in the Ni₃Al phase delineate the respective roles of the distance of the dislocation to the nearest free surface, of the anisotropic elasticity character of the material, and of the diffraction conditions used.