Grain Boundary Characters and Sliding of [0001] Symmetric Tilt Boundaries in Alumina
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Grain Boundary Characters and Sliding of [0001] Symmetric Tilt Boundaries in Alumina Katsuyuki Matsunaga1, Hitoshi Nishimura2, Hiroyuki Muto3, Takahisa Yamamoto4 and Yuichi Ikuhara1 1 Institute of Engineering Innovation, The University of Tokyo, 2-11-16, Yayoi, Bunkyo-ku, Tokyo, 113-8656, Japan. 2 Department of Materials Science, School of Engineering, The University of Tokyo, 2-11-16, Yayoi, Bunkyo-ku, Tokyo, 113-8656, Japan. 3 Department of Materials Science, Faculty of Engineering, Toyohashi University of Technology, 1-1, Hibarigaoka, Tenpaku-cyo, Toyohashi, Aichi, 441-8580, Japan. 4 Department of Advanced Materials Science, Graduate School of Frontier Sciences, The University of Tokyo, 2-11-16, Yayoi, Bunkyo-ku, Tokyo 113-8656, Japan. ABSTRACT Bicrystal experiments were performed to investigate atomic structures and high-temperature creep properties of [0001] symmetric tilt grain boundaries in Al2O3. Al2O3 bicrystals with Σ7, Σ31 and Σ39 boundaries were fabricated by a diffusion bonding technique, and their atomic arrangements at the grain boundary cores were analyzed by high-resolution transmission electron microscopy (HRTEM), in combination with static lattice calculations based on two-body ionic potentials. Compressive creep tests were also conducted to examine the behavior of grain boundary sliding for the above bicrystals. It was found that the behavior of grain boundary sliding depends on the grain boundary characters, whereas the trend of grain boundary sliding was not related to their Σ values. In contrast, HRTEM observations showed that the Σ31 boundary exhibiting the highest sliding rate has open spaces at the boundary core. Since grain boundary diffusion is expected to accommodate strains at grain boundary cores during sliding, it is likely that such open spaces give rise to high diffusivity at the grain boundary core, which results in the rapid grain boundary sliding of Σ31. INTRODUCTION Macroscopic structural and functional properties of ceramic materials strongly depend on grain boundaries. Since grain boundary properties are closely related to grain boundary structures, it is important to understand a relationship between structures and properties of grain boundaries. Since polycrystalline or nanocrystalline ceramic materials contain grain boundaries with a variety of grain boundary characters, however, we cannot easily clarify detailed atomic
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structures and the relevant properties at individual grain boundaries by conventional experiments using polycrystalline materials. In contrast, bicrystal experiments are advantageous to be performed, because grain boundary characters such grain misorientation can be unambiguously defined and controlled [1-4]. In this study, atomic structures and high-temperature mechanical properties of grain boundaries in α-alumina (Al2O3) were investigated using bicrystals. Al2O3 bicrystals with [0001] symmetric tilt grain boundaries were obtained by a diffusion bonding technique, and the grain boundary structures were observed by high-resolution transm
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