Study of dislocation structures near fatigue cracks using electron channelling contrast imaging technique (ECCI)

The fatigue of copper single crystals, orientated for single slip, has been studied using electron channelling contrast imaging in a scanning electron microscope. With the incident beam set at the Bragg condition, changes in the backscattered electron intensity occur as the beam is scanned over disl ocations that cause a local tilting of the diffraction planes. This techniq ue allows the evolution of dislocation structures over large areas to be fo llowed through different stages of the fatigue life. Furthermore, it enable s direct imaging of dislocation configurations at crack tips. The technique is compared with transmission electron microscopy and electron backscatter diffraction in its application to fatigue studies.