Void Formation in Aluminum Bicrystals Subjected to Cyclic Reversed Bending

Grain-boundary voids are found when aluminum bicrystals of non-symmetric orientation are subjected to cyclic reversed bending. The voids are most prominent in specimens with endurances of about 106 cycles and less. Fatigue cracks are found to initiate at and propagate from these voids. Electron microscope studies of thin foils taken from the boundary region reveal a dislocation structure of sub-boundaries and loops. A similar structure is found in areas remote from the boundary. From oxide replicas of the boundary region, jogs are observed where slip bands intersect the boundary. Multiple slip is not observed. It is suggested that voids nucleate where subgrain boundaries intersect the main boundary.It is suggested that voids nucleate where subgrain boundaries intersect the main boundary.