Investigation of grain boundary faceting phase transitions in aluminium
Project 01-02-16473 funded by
Russian Foundation for Basic Research







Head of the project
D. Sc. B. B. Straumal - leading research scientist

Participants

  • Dr. V. G. Sursaeva - senior research scientist
  • Dr. A. N. Aleshin - senior research scientist
  • Ing. S. G. Protasova - research scientist
  • Ing. S. A. Polyakov- junior research scientist
  • M. B. Juskov - technician

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    Faceting is a well documented phenomenon known both for surfaces and interfaces, particularly, grain boundaries (GBs). Faceting can be considered as a phase transition when the original surface or GB dissociates onto flat segments whose energy is less than that of the original surface or GB. For the investigation of GB faceting a cylindrical Cu bicrystal with an island grain was grown by the Bridgman technique. Grain 1 in this bicrystal is completely surrounded by grain 2. The dissociation Sigma-9 =  Sigma-9+ Sigma-3 proceeds during the growth of the bicrystal. The twins appear instead of {111}1/{115}2 or (110)S9CSL facet. GB faceting was studied at 1293 K, 1073 K, and 873 K The profiles of the GB thermal groove were analysed by atomic force microscopy. Wulff-Herring plots and GB phase diagrams have been constructed for the ?3, ?9 and ?9+?3 GBs. With increasing temperature the facets with low-density CSL-planes disappear in the GB shape. GB roughening phase transition can be responsible for this phenomenon. In the second prat of the work Zn [1,1,2,0] flat single crystals were grown using the modified Bridgman technique from Zn of 99.999 wt. % purity. Individual elongated twin plates having very uniform thickness were produced with the aid of slight deformation of single crystals. Parallel elongated sides of the twin plate are formed by the coherent symmetric twin (1,1,0,2)1||(1,1,0,2)2 grain boundary (STGB) facets. Due to its optical anisotropy, zinc allows one to study the shape of the GB with the aid of polarised light. The stationary shape of the slowly migrating tip of the twin plate has been studied in situ. The hot stage of optical microscope was used. The temperature interval from 592 to 692 K was investigated. Below 632 K the twin tip contains only one plane facet 1 which is nearly parallel to the (1,1,0,2)2 plane and has the angle of 84° with the coherent STGB. Above 632 K the second facet 2 appears at the tip of the twin plate. This facet is nearly parallel to the (1,1,0,2)1 plane and has the angle of 46° with the coherent STGB. Between 632 and 682 K both 84° and 46° facets coexist, and 84° facet gradually disappear with increasing temperature. Above 682 K only 46° facet is present in the twin tip. The indications of the GB roughening phase transition were also observed, namely the edges of the facets become smoother with increasing temperature. The GB phase diagram for the twin GBs in zinc containing the lines of two GB faceting phase transitions has been constructed. Schematic Wulff-Herring diagrams explaining these transitions are presented. In the third part of the work Al flat bycrystals were grown using the modified Bridgman technique from Al of 99.999 wt. % purity. They will be used for investigation of faceting in Al in the next future.

    List of publications

    1. B. B. Straumal, H.-E- Schaefer, K. Reimann, M. D. Baro, A. P. Zhilyaev
    Grain boundary phase transitions and their influence on the properties of the nanocrystalline materials (in Russian)
    "Advanced materials and technologies. Innovations of XXI century"
    (Eds. Yu.A. Ossipjan et al.), Chernogolovka, Russia (2001) p. 23. ISBN 5-901674-02-09
    Download in PDF-format

    2. S.A. Polyakov, B.B. Straumal, V.G. Sursaeva
    Grain boundary faceting phase transitions in zinc (in Russian)
    "Advanced materials and technologies. Innovations of XXI century"
    (Eds. Yu.A. Ossipjan et al.), Chernogolovka, Russia (2001) p. 109. ISBN 5-901674-02-09
    Download in PDF-format

    3. B.B. Straumal, S.A. Polyakov, E. Bischoff, W. Gust, E.J. Mittemeijer
    Faceting of Sigma-3 and Sigma-9 grain boundaries in copper
    Interface Sci (2002) in press. Download in PDF-format

    4. B.B. Straumal, V.G. Sursaeva, S.A. Polyakov
    Faceting and roughening of the asymmetric twin grain boundaries in zinc
    Interface Sci (2002)  in press. Download in PDF-format

    Presentations at scientific conferences

    1. B.B. Straumal, S.A. Polyakov, E. Bischoff, W. Gust, E.J. Mittemeijer
    Faceting of Sigma-3 and Sigma-9 grain boundaries in copper
    10th International Conference on Intergranular & Interface Boundaries iib2001 (oral)
    July 2226, 2001, Haifa, Israel

    2. B.B. Straumal, V.G. Sursaeva, S.A. Polyakov
    Faceting and roughening of the asymmetric twin grain boundaries in zinc
    10th International Conference on Intergranular & Interface Boundaries iib2001 (poster)
    July 2226, 2001, Haifa, Israel

    3. B.B. Straumal, H.-E- Schaefer, K. Reimann, M.D. Baro, A. P. Zhilyaev
    Grain boundary phase transitions and their influence on the properties of the nanocrystalline materials (in Russian)
    Regional conference "Investigations and developments in the scientific towns of Moscow Region.
    Advanced materials and technologies. Innovations of XXI century" (poster)
    October 0105, 2001, Chernogolovka, Russia

    4. S.A. Polyakov, B.B. Straumal, V.G. Sursaeva
    Grain boundary faceting phase transitions in zinc (in Russian)
    Regional conference "Investigations and developments in the scientific towns of Moscow Region.
    Advanced materials and technologies. Innovations of XXI century" (poster)
    October 0105, 2001, Chernogolovka, Russia