Faceting of Σ3 and Σ9 grain boundaries in Cu-Bi alloys

The faceting of Sigma3 and Sigma9 tilt grain boundaries (GBs) has been studied in bicrystals of pure Cu and Cu-Bi alloys containing 2.5 x 10(-3), 10 x 10(-3) and 16 x 10(-3) at.% Bi. The Sigma3(100), Sigma9(100), Sigma9(-110), and Sigma9(-120) facets and non-CSL Sigma3 82degrees 9R facet were observed, where Sigma is the inverse density of coincidence sites. The ratio between GB energy, sigma(GB), and surface energy, sigma(sur), was measured by atomic force microscopy using the GB thermal-groove method. The GB energy and thermal-groove deepening rate increased slightly between 0 and 10 X 10(-3) at.% Bi for all facets studied. However, between 10 X 10(-3) and 16 x 10(-3) at.% Bi the GB energy increased dramatically [from a factor 2 for the Sigma9(110) facet to 15 times larger for the Sigma3(100) facet]. The thermal-groove deepening rate also increased by a factor of 10 in this concentration range. This change corresponds well with the GB solidus line (i.e., the formation of a stable layer of a liquid-like GB phase called GB prewetting) observed previously. Wulff diagrams were constructed using measured sigma(GB)/sigma(sur) values. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.