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 μm. The remaining columns of twins were sheared in the direction of the shear stress with little rotation of the twin boundaries.