DENSE DISLOCATION WALLS AND MICROBANDS ALIGNED WITH SLIP PLANES - THEORETICAL CONSIDERATIONS

Some of the dislocation boundaries in cold deformed f.c.c. metals at l ow and intermediate strains lie on crystallographic slip planes and ot hers have a macroscopic direction with respect to the sample axes (i.e , they are non-crystallographic). A model for the occurrence of the fo rmer type of dislocation boundaries is proposed. The model combines sl ip pattern analysis and dislocation theory. It is assumed (i) that the dislocations in the boundaries are generated by slip, (ii) that the d eformation temperature is low enough to exclude dislocation climb and (iii) that the driving force for formation of boundaries is minimisati on of the energy stored in the boundaries. Formation of crystallograph ic boundaries is predicted if two active slip systems in the same slip plane account for a large Fraction of the total slip. For single crys tals the agreement between predicted and experimentally observed cryst allographic and non-crystallographic boundaries is excellent. For diff erent grain orientations in poly crystalline aluminium specimens, the agreement between prediction and experiment is satisfactory in view of the complexity of polycrystal studies compared to studies of single c rystals. (C) 1997 Acta Metallurgica Inc.