High‐Temperature Environmental Strength Degradation of a Hot‐Pressed Silicon Nitride: An Experimental Test

High‐temperature environmental strength degradation of hot‐pressed silicon nitride ceramics is postulated to occur as a consequence of the properties of the noncrystalline inter‐granular phase being altered by cation diffusion from the environment. The model proposed is tested by comparing the strength before and after prolonged high‐temperature exposures to a calcium‐rich magnesium silicate. Two high‐temperature degradation regimes are identified, one in which the intergranular phase alone is affected, and the other, at still higher temperatures, where actual corrosion of the silicon nitride grains occurs.