Dislocation Structure of Strain Localized Region and Fatigue Crack Initiation in 70/30 Brass, 85/15 Brass and Pure Copper

Although a number of models for the formation of extrusions and intrusions have been proposed, most of them are not considered to be sufficient. It is not yet clear whether or not the same mechanism may be responsible for the formation of extrusions in 70/30 brass, 85/15 brass and pure copper with different capability of cross slip. In this paper, investigations on dislocation structures of strain localized regions and fatigue crack initiation in these metals subjected to a long term stress cycling in vacuum were carried out by means of transmission electron microscopy. The strain localized regions bounded by two adjacent active glide layers were observed in the favorably oriented grains. Such strain localized regions were in close association with the formation of extrusion and transcrystalline cracking. At the intersections of the strain localized regions and the grain boundaries, extrusion-type deformations were sometimes formed due to the restraints of slip motions by the neighbouring grains.