Polycrystalline Cu with hierarchy microstructures – ultrafine grains about 500nm and included twins several to tens of nanometers thick – showed maximum strength at an average twin thickness of 15nm. Li et al. (2010) reported that the primary plastic deformation transited from inclined dislocation gliding to de-twinning in nano-twinned Cu when the twin thicknesses decreased from 25 to 4nm. Their investigation showed that enhanced de-twinning accounted for the strength softening in nt-Cu. From the kinetic and energetic aspects of de-twining process, two models were derived. In the kinetic model, it was assumed that thermally activated dislocation nucleation was the controlling mechanism for plastic deformation, while the transformation energy associated with de-twinning was considered to be governing in the energetic model. Application of the models to the strain-rate sensitivity and the temperature dependence of the strength of nano-twinned Cu suggested that the energetic mechanism also played an important role in de-twinning in nano-twinned Cu.

The Kinetics and Energetics of Dislocation Mediated De-Twinning in Nano-Twinned Face-Centered Cubic Metals. Y.Wei: Materials Science and Engineering A, 2011, 528[3], 1558-66