Microstructural evolution in a Cu-Zr alloy processed by a combination of ECAP and HPT

A Cu-0.1% Zr alloy was processed by equal-channel angular pressing (ECAP) for up to 8 passes and the samples processed through 4 and 8 passes were then sectioned into disks and further processed by high-pressure torsion (HPT) for 5 turns. Measurements were taken for the microhardness distributions on cross-sectional planes of the ECAP billets and on the HPT disks and the microstructures were examined using transmission electron microscopy and electron back-scatter diffraction. The results demonstrate that a combination of ECAP and HPT leads to additional grain refinement, higher hardness values and a larger fraction of boundaries having high angles of misorientation. The minimum average grain sizes recorded in these experiments were ∼280 and ∼260 nm at the center and edge of a disk, respectively, after processing through 8 passes of ECAP and 5 turns of HPT. The results contrast with an earlier report using high-purity Cu where a combination of ECAP and HPT gave a mixture of ultrafine and coarse grains due to the occurrence of dynamic recrystallization during the torsional straining.