Computer simulation of the formation of fragments with medium-angle boundaries in shear bands

The formation and transformation of low-angle dislocation boundaries into medium-angle grain boundaries are analyzed using computer simulation in the particular case of plastic deformation localized in shear bands. The conditions of appearance of fragments with medium-angle boundaries in shear bands are determined. It is shown that the evolution of low-angle boundaries into medium-angle boundaries in a shear band proceeds due to the suppression of active plastic deformation inside a subgrain by the elastic fields of the disclinations that appear in the subgrain junctions as a result of the misfit of plastic rotations along the subgrain boundaries. When these conditions are met, a subgrain behaves like an undeformable inclusion in a surrounding matrix during continuing deformation and undergoes crystallographic rotation. In this case, the subgrain misorientation increases continuously, which leads to the transformation of initial low-angle dislocation boundaries into medium-angle and, in the limit, high-angle boundaries.