Samples of pure Cu, Cu-10wt%Zn and Cu-30wt%Zn, with stacking-fault energies of 78, 35 and 14mJ/m2, respectively, were processed using high-pressure torsion and by a combination of high-pressure torsion followed by cold-rolling. X-ray diffraction measurements indicated that a decrease in stacking-fault energy led to both a decrease in crystallite size and to increases in micro-strain, dislocation and twin densities for the high-pressure torsion and high-pressure torsion plus cold-rolling processed ultra fine-grained samples. When compared with processing by high-pressure torsion, subsequent processing by cold-rolling refined the crystallite size of all of the samples, increased the twin densities of ultra fine-grained bronze and brass, and increased the dislocation density in ultra fine-grained bronze. It also decreased the dislocation density in ultra fine-grained brass, and led to an unchanged dislocation density in ultra fine-grained Cu. The results suggested that there might be an optimum stacking-fault energy for dislocation accumulation in ultra fine-grained Cu-Zn alloys.

Evolution of Defect Structures during Cold Rolling of Ultrafine-Grained Cu and Cu–Zn Alloys - Influence of Stacking Fault Energy. Y.H.Zhao, Z.Horita, T.G.Langdon, Y.T.Zhu: Materials Science and Engineering A, 2008, 474[1-2], 342-7