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Oxygen-free copper was processed by equal-channel angular pressing (ECAP) at room temperature for 1, 4 and 8 passes and then the ECAP specimens were further deformed by dynamic testing at 298 K using a strain rate of 10 s -1 . Experiments were conducted to investigate the influence of the initial microstructures induced by ECAP on the subsequent grain refinement and mechanical properties after dynamic testing. The results show the strength of copper increased with increasing numbers of ECAP passes and a significant additional grain refinement was produced in the ECAP specimens through the dynamic testing. Thus, the initial grain sizes after ECAP for 1, 4 and 8 passes were ~16, ~4.4 and ~2.9 µm, respectively, and these values were reduced to ~400, ~330 and ~300 nm by dynamic testing, The grains were refined by conventional dislocation processes in the 1-pass specimen but there was evidence for dynamic recrystallization in the specimen processed by 8 passes.

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Ultrafine‐grained copper samples produced by high‐pressure torsion are stored at room temperature for 12 months to investigate microstructural stability and the self‐annealing phenomena. The results show that samples processed by low numbers of turns exhibit less thermal stability after storage for 12 months in comparison with samples processed by high numbers of turns. A significant decrease in the hardness is recorded near the edges of the discs processed by 1/4, 1/2, and 1 turn due to recrystallization and grain growth, whereas a minor drop in hardness values is observed in the samples processed by 3, 5, and 10 turns. This drop in hardness is related to a recovery mechanism.