Measurement of screw and edge dislocation density by means of X-ray Bragg profile analysis

The type of dislocations produced during plastic deformation is necessary to know for the fundamental understanding anisotropy of hardening processes. By studying X-ray line broadening in several reflections, the fraction of certain dislocation types can be determined experimentally. The contribution of strain to line broadening is generally anisotropic. On the basis of the dislocation model, the modified Williamson–Hall and Warren–Averbach procedures have been suggested where g and g2 are replaced by gC̄ and g2 C̄, with C̄ as the average dislocation contrast factor. C̄ can be evaluated theoretically for different crystal systems and different dislocation types, i.e. edges and/or screws, by numerical methods. On the other hand, by analyzing strain anisotropy C̄ can be determined from experiment. Comparing experimental with theoretical C-values the specific fraction of dislocation types can be determined. In the present paper this procedure has been carried out for fine grained Cu 99.9% for deformation well into stage III. The ratio starts with a high fraction (90%) of screw dislocations. During deformation up to ε=0.3 this picture changes in favor of edge dislocations (75%).