Deformation twins and related softening behavior in nanocrystalline Cu-30% Zn alloy

Nanocrystalline Cu-30% Zn samples were produced by high energy ball milling at 77 K and room temperature. Cryomilled flakes were further processed by ultrahigh strain high pressure torsion (HPT) or room temperature milling to produce bulk artifact-free samples. Deformation-induced grain growth and a reduction in twin probability were observed in HPT consolidated samples. Investigations of the mechanical properties by hardness measurements and tensile tests revealed that at small grain sizes of less than similar to 35 nm Cu-30% Zn deviates from the classical Hall-Petch relation and the strength of nanocrsytalline Cu-30% Zn is comparable with that of nanocrystalline pure copper. High resolution transmission electron microscopy studies show a high density of finely spaced deformation nanotwins, formed due to the low stacking fault energy of 14 mJ m-2 and low temperature severe plastic deformation. Possible softening mechanisms proposed in the literature for nanotwin copper are addressed and the twin-related softening behavior in nanotwinned Cu is extended to the Cu-30% Zn alloy based on detwinning mechanisms.