Influence of grain size on the density of deformation twins in Cu–30%Zn alloy

Mechanical properties of nanostructured (NS) materials are significantly affected by both grain size and twin density, and the twin density has a close relationship with the grain size. Therefore, it is fundamentally important to understand the influence of grain size on the density of deformation twins in NS materials. In this study, we selected Cu–30%Zn alloy as a model material to study this phenomenon, because it has low stacking fault energy of 7 mJ m−2 and twinning is its dominant deformation mechanism. High-pressure torsion (HPT), equal channel pressing (ECAP) and ECAP followed by rolling were used to achieve a wide range of grain size from about 3 μm to 70 nm. It is found that, with decreasing grain size, the average distance between deformation twins decreases gradually from 177 nm to 24 nm, while the density of deformation twins (the length of twin boundary in unit area) exhibit a maximum value at ECAP + 95% rolling sample with average grain size of 110 nm. Careful statistics analysis reveals two optimum grain size ranges 60–80 nm and 40–50 nm for maximum twin density values for ECAP + 95% rolling and HPT Cu–30%Zn samples, respectively. The underlying mechanisms governing the influence of grain size on twinning is discussed.