The stability of oxygen‐free copper processed by high‐pressure torsion after room temperature storage for 12 months

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