Polycrystalline Cu with hierarchical microstructures – ultrafine grains of about 500nm and included twins several to tens of nanometers thick – exhibited maximum strengths at an average twin thickness of 15nm. Li et al. (Nature, 2010) reported that the primary plastic deformation transits from inclined dislocation gliding to de-twinning in nano-twinned Cu when twin thicknesses decreased from 25 to 4nm. Their investigation showed that enhanced de-twinning accounts for the strength softening in nt-Cu. Two models were presented for the kinetic and energetic aspects of the de-twining process. 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 govern the energetic model. Application of the models to the strain-rate sensitivity and temperature dependence of the strength of nano-twinned Cu suggested that the energetic mechanism also plays an important role in the de-twinning of 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