Grain-Boundary Wetting-Dewetting in z= 1 SiAlON Ceramic |
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Authors: | Hans-Joachim Kleebe Giuseppe Pezzotti |
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Affiliation: | Metallurgical and Materials Engineering Department, Colorado School of Mines, Golden, Colorado 80401;Department of Materials, Kyoto Institute of Technology, Sakyo-ku, Matsugasaki, 606–8585 Kyoto, Japan |
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Abstract: | The grain-boundary structure of a model SiAlON polycrystal with nominal composition Si5AlON7 was characterized by transmission electron microscopy (TEM) both in an equilibrium (as-processed) state at room temperature and after quenching from elevated temperature. In addition, low-frequency (1–13 Hz) internal friction data were recorded as a function of temperature, showing a pronounced grain-boundary sliding peak positioned at 1030°C. High-resolution transmission electron microscopy (HRTEM) of the equilibrated low-temperature microstructure revealed residual glass only at multigrain junctions, but no amorphous intergranular films were observed. The detection of clean interfaces in the as-processed sample contradicts the internal friction data, which instead suggests the presence of a low-viscosity grain boundary phase, sliding at elevated temperatures. Therefore, a thin section of the as-sintered material was heated to 1380°C and rapidly quenched. HRTEM analysis of this sample showed, apart from residual glass pockets, wetted grain boundaries, which is in line with the internal friction experiment. This wetting-dewetting phenomenon observed in z = 1 SiAlON is expected to have a strong impact not only on high-temperature engineering ceramics but also on geological, temperature-activated processes such as volcanic eruptions. |
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Keywords: | grain boundaries wetting SiAlON |
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