Dislocation structures in the strain localized region in fatigued 85/15 brass

Abstract

The correlation between the formation of extrusions and the dislocation structures in polycrystalline 85/15 brass subjected to a long term stress cycling with a low strain amplitude in vacuum was examined by means of transmission electron microscopy. The overall dislocation structures consisted of two types of structures,i.e., copper-type and 70/30 brass-type. Within them the strain localized regions bounded by two closely located active slip layers were frequently observed. In these boundary layers appeared a fringe pattern which was suggestive of intensive slip. Extrusions were formed in close association with the two closely located layers, and the initiation and growth of fatigue cracks occurred along one of them. On the basis of these observations, the mechanism of extrusion formation and of fatigue crack initiation are discussed.