Small-angle scattering by dislocations

It is shown that the small-angle scattering of X-rays or neutrons by disloc ations within a deformed metal, which are partially ordered into wall-like structures, is characterized by several factors. Principally these are asso ciated with: (i) a single dislocation or dipole; (ii) the dislocation confi guration in the plane of the wall; and (iii) the distribution of dislocatio ns across the wall thickness. With the assumption of isotropic elasticity, small-angle scattering will be sensitive only to the edge components of the dislocations. The scattered intensity is dominated by scattering from disl ocations that lie perpendicular to the scattering vector, q, and reaches a maximum when q is normal to the slip plane of these dislocations. Above a p articular \q\, the scattered intensity is sensitive only to the total edge dislocation content of the scattering dislocations (i.e, scattering is inco herent), while, below this value, the scattering is dominated by how the di slocations are distributed in walls. For walls normal to their slip planes, the configuration factor will reflect the dislocation distribution in the plane of the wall, while, for walls parallel to their slip planes, the dist ribution in the thickness direction will be visible. Therefore, even though a deformed material is composed of complicated dislocation structures, onl y those segments conforming to these rather strict prescriptions will be si ngled out for scattering, and, by adjusting the beam/slip system geometry, many parameters of the microstructure can be determined experimentally.