Syalon Ceramic for Application at High Temperature and Stress

Abstract

In the quest for a Si₃N₄-based ceramic to meet the requirements of hot-gas flow components in future turbines, the microstructure of a syalon ceramic has been refined by post-sintering heat treatments.

The achievement of oxidation resistance and non-cavitational creep at stress/temperature combinations of 100MPa/1300°C has previously been demonstrated for a syalon ceramic pressureless sintered with a Y—Si—Al—O—N liquid phase in which the matrix phase has subsequently been crystallised as YAG (3Y₂O₃.5Al₂O₃).

The temperature ceiling for application in oxidising environments is determined by the reversion of YAG to eutectic liquid by reaction with a SiO₂-rich oxidation layer.

In this paper a description is given of enhanced high-temperature performance via improved processing, optimisation of crystallisation and the formation of a YAG-free surface microstructure composed of β’-Si₃N₄ and Si₂N₂O. In particular a stress /temperature combination, unmatched by other comparable Si₃N₄ ceramics at 1375°C and 400 MPa has been achieved in bend and compressive creep at low strain rates via a diffusional mechanism, without cavitation.