An investigation of hardness homogeneity throughout disks processed by high-pressure torsion

Experiments were conducted on high-purity aluminum to determine the degree of hardness homogeneity attained during processing by high-pressure torsion (HPT). The HPT processing was conducted at room temperature using several disks of identical initial thickness with an applied pressure of 6.0 GPa and torsional straining from 1/4 to 20 turns. Following HPT, the flow patterns were observed by optical microscopy and values of the Vickers microhardness were recorded on different planes. The results show that, for any selected processing conditions, the distributions of microhardness values and the appearance of the etched surfaces in optical microscopy are independent of the plane of sectioning within the HPT disks. There is also a gradual evolution in homogeneity with increasing numbers of revolutions so that the microhardness values reach a constant value after 20 turns.