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Abstract
To clarify the effect of grain orientation on the evolution of dislocation structures in metals of medium-to-high stacking fault energy, detailed TEM characterization of structures was carried out for more than 350 individual grains in Al and Cu deformed in tension or by cold rolling up to moderate strain levels (ϵvM ≤ 0.8). Efforts were made to obtain a precise description of the three-dimensional arrangement of the dislocation structures and to determine the crystallographic plane of extended dislocation boundaries (geometrically necessary boundaries). A universal pattern of structural evolution characterized by a formation of three types of structure was found in both metals, irrespective of material parameters (stacking fault energy, grain size and impurity) and deformation conditions (deformation mode, strain and strain rate). The key parameter controlling the formation of the different structural types was found to be grain orientation with respect to the deformation axis (axes) and a clear relationship between the structural type and the grain orientation was established. A review of single crystal data shows a similar relationship. The grain orientation dependence of the structural type and similar structural types observed in tension and rolling suggest a common cause. Part II explores this by relating the structural types to the active slip systems.
Acknowledgements
The authors are grateful to Dr N. Hansen for enthusiastically contributing to numerous discussions on the subject over many years. Dr A. Godfrey, Dr D. Juul Jensen, Dr T. Leffers, Professor B. Ralph and Professor J. Wert are also thanked for their valuable comments. J. Lindbo and G. Christiansen are acknowledged for their skillful preparation of the TEM thin foils used in this study. The authors also gratefully acknowledge the Danish National Research Foundation for supporting the Center for Fundamental Research: Metal Structures in Four Dimensions, within which this work was performed.