Effect of High‐Temperature Exposure in Air on Strength of Hot‐Pressed Silicon Nitride

Short‐term exposure of hot‐pressed Sl 3 N 4 to high temperature (800°C) eradi cates the truncated strength distribution produced by room‐temperature proof‐testing, indicating that strengths after high‐temperature exposure are determined by jaws different from preexisting flaws. Since acid polishing of proof‐tested samples cycled to high temperature restored the truncated after‐proof strength distribution, it is believed that short‐term high‐temperature exposure causes amor phous SiO 2 to form on the surface, thus blunting the surface flaws.