EFFECT OF GRAIN SIZE ON THE GRAIN BOUNDARY CHARACTER DISTRIBUTIONS OF COLD ROLLED AND ANNEALED PURE COPPER

Pure copper (99.97%) samples with varied grain sizes were cold rolled and annealed at first and then their grain boundary character distributions (GBCDs) were characterized by electron back scatter diffraction (EBSD) techniques. The results showed that the sample with finer initial grain size (12 pan) appeared to be largely populated by the so-called special boundaries such as Sigma 3(n) (n=1, 2, 3) after cold rolling and annealing, the fraction of Sigma 3(n) boundaries reached 75.7% and the averaged size of clusters of grains with Er (n=1, 2, 3) orientation relationships (Sigma 3(n) CG) were as large as 200 mu m in this sample. However, with initial grain size increasing, the fraction of special grain boundaries as well as the size of Sigma 3(n) CG in the samples were decreasing dramatically. In situ EBSD observation, twin-filtering and five parameter method (FPM) analyses indicated that triple-junctions are the preferred sites for the nucleation of incoherent Sigma 3 boundaries which play a important role in enhancing the fraction of special boundaries. It accounts for primarily the desired GBCD results as obtained in the sample with finer initial grain size.