High-pressure torsion of copper samples containing columns of highly aligned nanotwins

Copper disks containing columns of aligned nanotwins were subjected to high-pressure torsion (HPT) involving a half turn under a 3 GPa compressive stress. The overall shear strain of 21 at 1 mm from the center of rotation is concentrated at the surfaces, where the columns of twins have been transformed into a 3-D grain structure to a depth of about 5 mu m. The remaining columns of twins were sheared in the direction of the shear stress with little rotation of the twin boundaries. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.