Dislocation content of geometrically necessary boundaries aligned with slip planes in rolled aluminium

Abstract

Previous studies have revealed that dislocation structures in metals with medium-to-high stacking fault energy, depend on the grain orientation and therefore on the slip systems. In the present work, the dislocations in eight slip-plane-aligned geometrically necessary boundaries (GNBs) in three grains of near 45° ND rotated cube orientation in lightly rolled pure aluminium are characterized in great detail using transmission electron microscopy. Dislocations with all six Burgers vectors of the ½⟨1 1 0⟩ type expected for fcc crystals were observed but dislocations from the four slip systems expected active dominate. The dislocations predicted inactive are primarily attributed to dislocation reactions in the boundary. Two main types of dislocation networks in the boundaries were identified: (1) a hexagonal network of the three dislocations in the slip plane with which the boundary was aligned; two of these come from the active slip systems, the third is attributed to dislocation reactions (2) a network of three dislocations from both of the active slip planes; two of these react to form Lomer locks. The results indicate a systematic boundary formation process for the GNBs. Redundant dislocations are not observed in significant densities.

Keywords:

• dislocation boundaries
• dislocations
• slip systems
• transmission electron microscopy (TEM)
• weak beam
• aluminium

Acknowledgements

The authors gratefully acknowledge support from the Danish National Research Foundation (Grant No. DNRF86-5) and the National Natural Science Foundation of China (Grant No. 51261130091) for the Danish-Chinese Center for Nanometals, within which this work was performed. The authors thank N. Hansen and A. Godfrey for valuable comments on the manuscript, and E. Johnson, A. Ramar and T. Yu for helpful discussions on the TEM experiments.