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Formation of in-situ reinforced microstructure in α–sialon ceramics I: Stoichiometric oxygen-rich compositions

Published online by Cambridge University Press:  31 January 2011

Zhijian Shen*
Affiliation:
Department of Inorganic Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden
Hong Peng
Affiliation:
Department of Inorganic Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden
Mats Nygren
Affiliation:
Department of Inorganic Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden
*
a) Address all correspondence to this author. e-mail: [email protected]
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Abstract

The abnormal grain growth in α–sialon ceramics was investigated. The preparations had stoichiometric compositions on the oxygen-rich phase boundary, and they were stabilized by Y, Nd, Sm, Dy, and Yb, respectively. Specimens were prepared from α–Si3N4 as precursor powder by applying conventional hot pressing and a novel rapid consolidation process, namely spark plasma sintering (SPS). Single-phase α–sialon ceramics with in situ reinforced bimodal microstructure, i.e., large elongated grains embedded in a matrix consisting of small equiaxed grains, were obtained above 1750 °C in all systems compacted by SPS and above 1800 °C in systems stabilized by Nd and Sm but not Dy, Y, or Yb by a two-step hot-pressing procedure. It was observed that the formation of abnormally grown α–sialon grains was strongly temperature-dependent, indicating that it was encouraged by the formation of a transient liquid phase that stimulated the dissolution of any remaining nitride precursors and early formed small α–sialon grains and sequentially facilitated supersaturation by the α–sialon constituents. The presence of elongated grains improves fracture resistance in the obtained materials.

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Articles
Copyright
Copyright © Materials Research Society 2002

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References

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