Characterizing dislocation structures in bulk fatigued copper single crystals using electron channelling contrast imaging (ECCI)

Fatigue of copper single crystals, oriented for single slip, has been studied using electron channelling contrast imaging (ECCI) in a scanning electron microscope. This technique was used to detect and characterize dislocation structures in bulk specimens. With the incident beam set at the Bragg condition, changes in the backscattered electron intensity occur as the beam is scanned over dislocations which cause a local tilting of the diffraction planes. ECCI observations on specimens fatigued up to the saturation plateau (resolved shear stress tau(s) = 28 MPa) show that the dislocation substructures, principally ladder structures and elongated cells, are identical to those observed using transmission electron microscopy on thin foils. One of the main advantages of the ECCI technique is that one can follow all stages of the formation and evolution of dislocation structures over large areas in the same bulk specimen during fatigue interrupted at different stages of the fatigue life. ECCI should prove a powerful tool for investigating dislocation configurations at crack tips or at extrusions/intrusions or persistent slip band systems.