The high temperature creep deformation of Si₃N₄-6Y₂O₃-2Al₂O₃

The creep properties of silicon nitride containing 6 wt % yttria and 2 wt% alumina have been determined in the temperature range 1573 to 1673 K. The stress exponent, n, in the equation {Mathematical expression} ∝ σⁿ was determined to be 2.00±0.15 and the true activation energy was found to be 692±25 kJ mol^-1. Transmission electron microscopy studies showed that deformation occurred in the grain boundary glassy phase accompanied by microcrack formation and cavitation. The steady state creep results are consistent with a diffusion controlled creep mechanism involving nitrogen diffusion through the grain boundary glassy phase.