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Microstructural characterization of a microwave-sintered silicon nitride based ceramic

Published online by Cambridge University Press:  03 March 2011

Kevin P. Plucknett*
Affiliation:
Department of Materials Science and Engineering, McMaster University, Hamilton, Ontario, L8S 4L7, Canada
David S. Wilkinson
Affiliation:
Department of Materials Science and Engineering, McMaster University, Hamilton, Ontario, L8S 4L7, Canada
*
a)Present address: Metals and Ceramics Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831–6068.
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Abstract

The microstructure of a microwave-densified silicon nitride based ceramic has been assessed in the as-sintered, post-sinter hot-isostatically pressed (HIPed) and annealed conditions. The grain size of the as-sintered material, which is a low substitution β′-Sialon, was significantly finer than observed in conventionally processed materials of similar composition. The as-sintered ceramic exhibits a reverse porosity gradient (with the highest porosity level at the surface) due to heat dissipation to the cooler surroundings during microwave processing. This also results in a higher β′ aspect ratio close to the surface arising from an increased glass viscosity (due to heat loss) and compositional change in this region during sintering. HIPing results in removal of all porosity from the sample core; however, a reduced porosity surface layer is retained. Significant β′-Sialon grain growth is also apparent after HIPing. A fine β′ grain structure was retained after annealing, with partial devitrification of the glassy grain boundary phase to β-Y2Si2O7.

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Copyright
Copyright © Materials Research Society 1995

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