SiAlON bulk glasses and their role in silicon nitride grain boundaries: Composition-structure-property relationships

Stuart Hampshire, Michael J. Pomeroy

Research output: Contribution to journalArticlepeer-review

Abstract

SiAlON glasses are silicates or alumino-silicates, containing Mg, Ca, Y or rare earth (RE) ions as modifiers, in which nitrogen atoms substitute for oxygen atoms in the glass network. These glasses are found as intergranular films and at triple point junctions in silicon nitride ceramics and these grain boundary phases affect their fracture behaviour. This paper provides an overview of the preparation of M-SiAlON glasses and outlines the effects of composition on properties. As nitrogen substitutes for oxygen in SiAlON glasses, increases are observed in glass transition temperatures, viscosities, elastic moduli and microhardness. These property changes are compared with known effects of grain boundary glass chemistry in silicon nitride ceramics. Oxide sintering additives provide conditions for liquid phase sintering, reacting with surface silica on the Si 3N 4 particles and some of the nitride to form SiAlON liquid phases which on cooling remain as intergranular glasses. Thermal expansion mismatch between the grain boundary glass and the silicon nitride causes residual stresses in the material which can be determined from bulk SiAlON glass properties. The tensile residual stresses in the glass phase increase with increasing Y:Al ratio and this correlates with increasing fracture toughness as a result of easier debonding at the glass/β-Si 3N 4 interface.

Original languageEnglish
Pages (from-to)301-307
Number of pages7
JournalJournal of the Korean Ceramic Society
Volume49
Issue number4
DOIs
Publication statusPublished - Jul 2012

Keywords

  • Fracture resistance
  • Grain boundary
  • Oxynitride glasses
  • Residual stress
  • Silicon nitride
  • Sintering additives
  • Thermal expansion mismatch

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