Microstructural Changes in Nanotwinned Cu Resulting from Unidirectional and Reversed High Pressure Torsion

The response of the microstructure of Cu samples containing aligned columns of nanotwins to extreme shear stress produced by high pressure torsion has been studied. The torsion was applied both in one direction only and reversed. It is found that under conditions of unidirectional torsion in which the overall shear strain is about 20, the shear deformation is largely confined to the near surface regions. The twins are destroyed to the depth at which the shear strain drops to about 1. Repeated reversal of the torsion up to the same overall shear strain destroys the twin structure altogether, leading to elongated grains of about 1 micrometer in length. Data will be presented of results of testing over a range of maximum torsions and numbers of reversals.