Kazuhiro Okamoto1, Hans-Joachim Kleebe2,Ken'ichi Ota3 and Giuseppe Pezzotti1
1Department of Materials, Kyoto Institute of Technology, Kyoto 606-8585
The changes of ceramics properties are influenced by a microstructure, namely grain size and grain boundary. Available silicon nitride ceramic powder is usually covered with very thin silicon oxide layer. This silicon oxide is the origin of a glass film at grain boundaries. The purpose of this paper is to produce the new SiAlON materials (Si6-ZAlZOZN8-Z) which were controlled glass film. SiAlONs (with Z=1, 2, 3) were hot isostatically pressed (HIPed) at 2273 K under an argon-gas pressure of 180 MPa using high-purity SiAlON powders (Ube Industries). We can obtain SiAlON ceramics without glass film at grain boundary. Microscopy studies revealed the presence of a 15R SiAlON phase precipitated at the grain boundaries or triple-grain junctions of Z=2, 3 SiAlONs. Z=1 SiAlON revealed presence of glass-SiO2 grain boundary structure in which a conspicuous amount of Al was found. The viscous behavior of grain boundary at high temperature was studied by the internal friction method. Internal friction data collected up to very high temperatures showed no grain boundary relaxation peak in the Z=2, 3 SiAlON materials, and a relaxation peak centered at a rather low temperature in the Z=1 SiAlON.
(Received April 15, 1999; In Final From September 13, 1999)
high-purity SiAlON, internal friction, grain boundary viscosity, grain boundary sliding, high resolution electron microscopy
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