Temperature influence on the faceting of Sigma 3 and Sigma 9 grain boundaries in Cu

The faceting of a tube-like tilt grain boundary (GB) in Cu bicrystals has been studied in the temperature interval from 0.5 to 0.95 of the melting temperature T-m (T-m = 1356 K). The grains of the bicrystals form the coincidence site lattice (CSL) with inverse density of coincidence sites Sigma = 3 and Sigma = 9. No rounded edges between facets were observed up to 0.95T(m). With decreasing temperature new facets of increasingly higher CSL indices appear. At 0.5T(m) six crystallographically different Sigma = 3 facets exist simultaneously. The appearance of high-index CSL facets can be explained by the roughening phase transition of a Kosterlitz-Thouless type. The ratio of GB energy sigma(GB) and surface energy sigma(sur) of the specimen was measured by applying atomic force microscopy to the profile of the GB thermal groove formed upon additional annealing. The Wulff Herring diagrams were constructed using measured sigma(GB)/sigma(sur) values. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.