The effect of bismuth segregation on the faceting of Σ3 and Σ9 coincidence boundaries in copper bicrystals

Abstract

Abstract The faceting of a cylindric tilt grain boundary (GB) in Cu and Cu-160 ppm Bi bicrystals was studied. The crystal lattices of both grains form a superlattice called a coincidence site lattice (CSL) with an inverse density of coincidence sites relating to the density of lattice sites Σ = 3 and Σ = 9. The Σ3 and Σ9 <110> tilt GBs became faceted upon annealing at 0.95 T m . The ratio of GB energy σ GB and surface energy σ sur of the specimen was measured, applying atomic force microscopy, from the profile of the GB thermal groove formed upon additional annealing. The 160 ppm Bi concentration in the Bi-containing bicrystal is between GB and bulk solidus lines in the Cu – Bi phase diagram. In this concentration region GBs contain a multilayer Bi-rich film which is supposed to be liquid-like. Wulff – Herring diagrams were constructed using the measured σ GB /σ sur values , revealing stable and metastable GB facets.