CHARACTERIZING DISLOCATION-STRUCTURES IN BULK FATIGUED COPPER SINGLE-CRYSTALS USING ELECTRON CHANNELING CONTRAST IMAGING (ECCI)

Fatigue of copper single crystals, oriented for single slip, has been studied using electron channelling contrast imaging (ECCI) in a scanni ng electron microscope. This technique was used to detect and characte rize dislocation structures in bulk specimens. With the incident beam set at the Bragg condition, changes in the backscattered electron inte nsity occur as the beam is scanned over dislocations which cause a loc al tilting of the diffraction planes. ECCI observations on specimens f atigued up to the saturation plateau (resolved shear stress tau(s) = 2 8 MPa) show that the dislocation substructures, principally ladder str uctures and elongated cells, are identical to those observed using tra nsmission electron microscopy on thin foils. One of the main advantage s of the ECCI technique is that one can follow all stages of the forma tion and evolution of dislocation structures over large areas in the s ame bulk specimen during fatigue interrupted at different stages of th e fatigue life. ECCI should prove a powerful tool for investigating di slocation configurations at crack tips or at extrusions/intrusions or persistent slip band systems.