Dislocation Structure Near the Intergranular Fracture Surface of Cyclically Strained Polycrystalline Copper

ABSTRACT Polycrystalline copper specimens were cycled with strain amplitudes, resulting in fatigue lives ranging from 10 5 to 10 7  cycles. The fracture surfaces were inspected in the SEM, and intergranular facets with surface relief were studied. FIB sections were produced, and lamellae for the TEM were prepared using FIB sectioning. Individual persistent slip markings on the facets, consisting of distinctive extrusions and intrusions, were inclined at an angle to the surface corresponding to the trace of the primary slip plane. Dislocation structures close to the surface of the facets were observed and analyzed. The dislocation structure consisted of randomly distributed dislocations and some dislocation sub‐boundaries. Contrary to the dislocation structure below the specimen surface, no specific dislocation structures corresponding to the persistent slip bands were found. The absence of localized cyclic strain‐induced dislocation patterns was discussed and attributed to the complex stress and strain history within the cyclic plastic zone of the propagating crack, where multiple slip systems were active.