By means of dynamic plastic deformation at liquid-nitrogen temperatures, bulk nano-grained samples with embedded nano-twin bundles were prepared. Subsequent cold-rolling of the liquid-nitrogen temperature dynamic plastically-deformed material led to a reduction in the incidence of nano-twin bundles and to slight grain-coarsening, accompanied by a decrease in grain-boundary energy from 340 to 220mJ/m2.

Mechanical Properties and Rolling Behaviors of Nano-Grained Copper with Embedded Nano-Twin Bundles. Y.Zhang, N.R.Tao, K.Lu: Acta Materialia, 2008, 56[11], 2429-40