Twenty-five years of severe plastic deformation: recent developments in evaluating the degree of homogeneity through the thickness of disks processed by high-pressure torsion

The processing of disks by high-pressure torsion leads to an inhomogeneous distribution in strain with a high strain around the perimeter of the disk and a zero strain in the center. Despite this apparent inhomogeneity, there are now many experiments showing that the hardness values on the surfaces of disks gradually evolve with increasing strain to give a reasonably high level of homogeneity. Experiments were conducted to determine whether this high level of homogeneity extends also through the thickness of the disks or whether inhomogeneities occur in the axial direction. Results are presented for high-purity aluminum and a magnesium AZ31 alloy as two representative materials showing different hardness characteristics.