Electron channelling contrast imaging characterization of dislocation structures associated with extrusion and intrusion systems and fatigue cracks in copper single crystals

The fatigue of copper single crystals, oriented for single slip, was studie d using electron channelling contrast imaging (ECCI) in a scanning electron microscope. This technique allows the detection and characterization of di slocation structures in bulk specimens. This paper presents ECCI images sho wing dislocation arrangements associated with intrusions, extrusions and st age I and stage II cracks in single-crystal copper samples fatigued by tens ion-compression along [541]. The presence of intrusions or stage I cracks o n the persistent slip band (PSB) planes caused no noticeable change in the local dislocation structures in the matrix vein and PSB ladder structures. Stage II cracks deviate from the PSB planes and were associated with elonga ted dislocation cells inclined in the direction of the loading axis. These elongated dislocation cells are confirmed to within 10 mum of the crack tip .