SEM imaging of the cell structure of dislocation networks in cold worked cu single crystals

Abstract

In certain metallurgical applications of SEM, such as the observation of deformation effects, and the recovery and recrystallization processes in bulk specimens, it is of special interest to obtain information about local inhomogeneities of the dislocation densities in a sample. This can be obtained using TEM on thin foils. Previously information on distortion in cold‐worked specimens was obtained by measuring the dependence of the deterioration of the resolution of the selected area channelling patterns (SACP) on the degree of deformation. This method, however, is not applicable to highly deformed materials. Direct SEM imaging of the cell structure of the dislocation network has been achieved without resolving single dislocations by using a suitable arrangement of specimen and detector, such that only backscattered electrons (BSE) leaving the surface at a large angle to the normal contribute to the image signals. The signal‐to‐noise ratio was improved to the degree that it was possible 1) to image the cell structure of the dislocation network and 2) on heating the specimens, to record the growth of recrystallized regions with TV‐frame frequency. The imaging of the cell structure gives qualitative information about the degree of crystal deformation and the crystallographic direction of grain boundary motion during recrystallization.

Electron channeling patterns in the scanning electron microscope

“…One sequence of operations ofthis type is usually sufficient to identify all the subgrains in a given area. The cell sizes deduced in this technique agree well with those found by more conventional TEM techniques (De Vries and Mastenbrock 1977;Schmidt et al 1978) although they are obtained much more quickly and from a wider area of the specimen than is possible in the TEM case. The minimum misorientation between cells can be estimated by noting the minimum change in angle of incidence that is needed to make any individual cell visible.…”

Detector system for backscattered electrons by conversion to secondary electrons

“…An electrolytically polished polycrystalline copper specimen shows a crystal orientation contrast ( Philibert and Tixier 1969, Newbury 1974, Schmidt et al 1978 which increases with decreasing primary electron energy. Fig.…”

The use of subgrains as imaged in the SEM from bulk specimens in the study of localized plasticity

“…In the SEM, it is possible to quickly and easily detect subgrains over large or small areas using electron channeling contrast. (Schmidt et al 1978). This paper describes the usefulness of this method in detecting subgrains as applied to fatigue and creep.…”