Dislocation structures in the strain localized region in fatigued 70/30 brass and the interaction with grain boundary

Long-term fatigue tests of polycrystalline 70/30 brass were carried out under low strain amplitudes in vacuum, and dislocation structures of the strain localized regions developed were examined by means of transmission electron microscopy In the planar dislocation structures, the strain localized regions (SLRs) bounded by a pair of parallel active glide layers were frequently observed in favorably oriented grains. Where the SLRs impinge on grain boundaries (GBs), extrusion-type deformations were sometimes formed notwithstanding the restraints of the neighboring grains. On the basis of observations, the mechanism of crack initiation at the GB is discussed.