The temperature influence on the faceting of Σ3 grain boundaries in aluminium

Grain boundary faceting can strongly influence the diffusion permeability of polycrystals and other diffusion-controlled phenomena like grain growth, grain sliding, etc. Faceting is a well known phenomenon for the grain boundary behaviour. Faceting can be considered as a phase transition when the grain boundary dissociates onto flat segments whose energy is less than that for the original grain boundary. For the investigation of grain boundary faceting a cylindrical Al bicrystal of 99.999% wt. purity was grown by the Bridgman technique. One grain in this bicrystal is semi-surrounded by another one. The bicrystal contains a coincidence tilt grain boundary Sigma 3 < 110 >. Bicrystalline samples were coated with a layer of Sn-Al mixture and annealed at different temperatures: 723 and 873 K. Contact angles at the junction of grain boundary and two solid/liquid interfaces were measured. Ratio of grain boundary energy and solid/liquid interface energy had been calculated. Wulff-Herring plots and grain boundary phase diagrams were constructed. Three crystallographic different facets were observed. Two of them remain stable at 723 K, the third one becomes metastable.