Electron channelling contrast as a supplementary method for microstructural investigations in deformed metals

Abstract

Electron channelling contrast is obtained in the scanning electron microscope by detecting back-scattered electrons created by a parallel incident electron beam. The intensity of the back-scattered electrons depends on the orientation of the incident beam with respect to the crystal lattice. In this report, several examples for the application of channelling contrast as a means for investigating the microstructure of metals after deformation are given. First, the change in dislocation glide mechanism during fatigue of the austenitic stainless steel AISI 304L as a function of deformation temperature is demonstrated by means of a comparative study by transmission electron microscopy and scanning electron microscopy (SEM) channelling contrast. The efficiency of channelling contrast in imaging dislocation arrangements is shown. In the next example, referring also to AISI 304L, it is shown that electron channelling contrast can also be applied advantageously to the study of subgrain structures in the direct vicinity of cavities and wedge cracks in the interior of the material. In another example, the technique is shown to be suitable for the identification of intercrystalline cracks along twins on the surface of a fatigued copper specimen. Such cracks are difficult to identify otherwise. The final examples illustrate for fatigued b.c.c. α-iron polycrystals that widely different dislocation arrangements which are formed, depending on the carbon content, can be distinguished and that surface cracks with adjacent dislocation cell structures can be studied easily by the SEM channelling technique.