Significance of strain reversals in a two-phase alloy processed by high-pressure torsion

Disks of the Zn–22% Al eutectoid alloy were processed in conventional monotonic high-pressure torsion (m-HPT) and under cyclic conditions where there are periodic reversals in the strain direction during processing (c-HPT). All samples showed significant grain refinement after HPT but there was a decrease in the hardness by comparison with the initial annealed condition. The measured grain sizes were smaller at the edges than in the centers of the disks for both testing conditions but the grain sizes were also consistently smaller when using c-HPT. The hardness values in the centers of the disks decreased with increasing strain in m-HPT but they remained high in c-HPT. It is shown that these results lead to a new and different variation of hardness with equivalent strain which should apply to any material where weakening is introduced due to a removal of precipitates because of the high applied pressure in the processing operation.