High temperature mechanical behaviour of silicon nitride ceramics

The high temperature mechanical behaviour of two silicon nitride-based cera mic materials has been studied; N 7202, made by low pressure sintering with yttria, alumina and magnesia as additives, and N 3208, made by high pressu re sintering with yttria and alumina as additives. Both materials are beta -silicon nitride. The results have been analysed in terms of the classical creep equation. The stress exponent was n = 0.4 for N 7202 and n = 0.5 for N 3208, whereas the average apparent activation energy was Q approximate to 500 kJ/mole for both materials. Transmission electron microscopy studies h ave allowed to determine the microstructural features of these materials.