Dislocation Structures in Aluminium Crystals Fatigued in Different Orientations

Polycrystalline aluminium sheet has been cycled to two stages of fatigue damage and the dislocation structures studied by transmission electron microscopy. The structures could be classified into a limited number of types, each characteristic of a particular stress axis. Direct correlation of the dislocation structures and the surface-deformation features was not achieved because of the presence of a dislocation-free zone at the crystal surfaces. Intuitive correlation, however, enabled models to be proposed linking surface and interior structures. Dislocation motion occurring within each structure during fatigue is discussed.