Experiments were conducted on samples of pure Cu and two Cu–Zn alloys in order to evaluate the influence of the stacking-fault energy on microstructural development when processing using high-pressure torsion. Transmission electron microscopy, X-ray diffraction and hardness measurements were used for microstructural evaluation and the results revealed  a consistency between these techniques. Grain sizes in the nm-range were formed at the edges of the high-pressure torsion disks, larger sub-micrometer grains were formed in the disk centers and the measured grain sizes decreased with decreasing stacking-fault energy. There was negligible twinning in pure Cu but the densities of dislocations and twins increased with increasing Zn content and thus with decreasing stacking-fault energy. The values of the Vickers microhardness were lower in the centers of the disks for the two Cu–Zn alloy and this was consistent with the low stacking-fault energy and slow rates of recovery.

Influence of Stacking-Fault Energy on Microstructural Characteristics of Ultrafine-Grain Copper and Copper–Zinc Alloys. L.Balogh, T.Ungár, Y.Zhao, Y.T.Zhu, Z.Horita, C.Xu, T.G.Langdon: Acta Materialia, 2008, 56[4], 809-20