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Abstract
The nature and behaviour of grain boundary (GB) phases is very important since they can control strength, plasticity, resistivity, grain growth, corrosion resistance, etc, especially in nanocrystalline materials. For nanocrystalline Al-based light alloys, extremely high plasticity has been observed in restricted temperature and concentration intervals close to the solidus line. This phenomenon is not fully understood. It can be explained by formation of GB phases not included in the bulk phase diagram. Therefore, the structure of GB phases, as well as thermodynamic conditions for their existence, has to be carefully studied. In this work the structure and composition of GBs and GB triple junctions in Al–5 at.% Zn polycrystals annealed in the temperature region above and below the bulk solidus line were studied by high-resolution electron microscopy and analytical transmission electron microscopy. Evidence has been obtained that a thin layer of a liquid-like phase exists in GBs and GB triple junctions slightly below the bulk solidus line.
Acknowledgements
The authors thank the Russian Foundation for Basic Research (contracts 06-03-32875 and 05-02-16528), German Federal Ministry for Education and Research (contract RUS 04/014) and INTAS (contracts 03-51-3779 and 05-109-4951). They also greatly appreciate Dr. W. Sigle (Max-Planck-Institut für Metallforschung, Stuttgart) for his help in the analytical microscopy investigations.