EVOLUTION OF HOMOGENEITY IN OXYGEN-FREE COPPER PROCESSED BY EITHER ECAP OR HPT

Oxygen-free copper having a commercial purity of 99.95 wt.% was processed at room temperature by severe plastic deformation (SPD) using either equal-channel angular pressing (ECAP) or high-pressure torsion (HPT). The ECAP billets were processed through a die having an internal angle of 110 degrees for up to 8 passes and the HPT discs were processed under an applied pressure of 6.0 GPa for up to 10 turns. The evolution of microstructural homogeneity was investigated for each process by measuring the grain sizes and recording the distributions of the microhardness values on the cross-sectional planes of the ECAP billets and on the disc surface planes of the HPT samples. For both sets of measurements, the hardness values were recorded following a rectilinear grid pattern in order to generate colour-coded maps of the hardness distributions.