The influence of grain-boundary structure on grain growth in copper subjected to severe plastic deformation was studied using orientation imaging microscopy. The investigation was carried out on oxygen-free high-conductivity copper which was wire drawn to a true strain of about 4 and processed by equal-channel angular extrusion to 4 and 8 passes via “route Bc” (where the billet was rotated by 90° in the same direction between consecutive passes). The grain-boundary character distribution of the as-drawn wire was similar to that of equal-channel angular extrusion-processed specimens, and both materials possessed a higher fraction of high-angle grain boundaries than special coincidence-site lattice boundaries. While the high fraction of high-angle grain boundaries was retained in the annealed wires, they were transformed to coincidence-site lattice boundaries in the annealed equal-channel angular extrusion-processed materials. In spite of an initially smaller grain size, when annealed (750C, 1h), the grain size of the 4-pass equal-channel angular extrusion-processed material was larger than that of the wire drawn to a similar strain. This difference was attributed to a high density of high-mobility 35–50° <001> boundaries in the 4-pass equal-channel angular extruded materials. On the other hand, the presence of 50–60° <111> pinning boundaries in the annealed 8-pass material accounted for the smaller grain size after recrystallization.

Grain-Boundary Structure of Oxygen-Free High-Conductivity (OFHC) Copper Subjected to Severe Plastic Deformation and Annealing. D.R.Waryoba, P.N.Kalu, R.Crooks: Materials Science and Engineering A, 2008, 494[1-2], 47-51