The faceting of Σ3 and Σ9 tilt grain boundaries was studied in bicrystals of pure Cu and Cu–Bi alloys containing 2.5 x 10−3, 10 x 10−3 and 16 x 10−3at%Bi. The Σ3(100), Σ9(100), Σ9(−110) and Σ9(−120) facets and non-CSL Σ3 82° 9R facet were observed, where Σ was the inverse density of coincidence sites. The ratio between grain boundary energy, σGB, and surface energy, σsur, was measured by atomic force microscopy using the grain boundary thermal-groove method. The grain boundary energy and thermal-groove deepening rate increased slightly between 0 and 10 x 10−3at%Bi for all facets studied. However, between 10 x 10−3 and 16 x 10−3at%Bi the grain boundary energy increased dramatically [from a factor 2 for the Σ9 (110) facet to 15 times larger for the Σ3 (100) facet]. The thermal-groove deepening rate also increased by a factor of 10 in this concentration range. This change corresponds well with the grain boundary solidus line (i.e., the formation of a stable layer of a liquid-like grain boundary phase called grain boundary prewetting) observed previously. Wulff diagrams were constructed using measured σGB/σsur values.

Faceting of Σ3 and Σ9 Grain Boundaries in Cu–Bi Alloys. B.B.Straumal, S.A.Polyakov, E.Bischoff, W.Gust, B.Baretzky: Acta Materialia, 2005, 53[2], 247-54