Cyclic Fatigue of Hot‐Pressed Si ₃ N ₄

The cyclic fatigue behavior of two grades of hot‐pressed silicon nitride was investigated. Flat, cantilever‐type specimens were tested at temperatures up to 1300°C, in air, where the load was applied by an eccentric driver rotating at 1800 rpm, with a zero mean stress. The lifetime of the lower purity material at temperatures up to 1200°C was controlled by a stress corrosion mechanism. Above 1200°, and for both grades of material, plastic deformation, probably by grain boundary sliding, was rate controlling.