Fatigue Crack Growth of Silicon Nitride at 1400°C: A Novel Fatigue‐Induced Crack‐Tip Bridging Phenomenon

high‐strength Si 3 N 4 with elongated β‐Si 3 N 4 and equiaxed α‐sialon was tested in cyclic and static fatigue at 1400°C. At low stress intensity factors and high frequencies, the pullout process of the elongated grains was enhanced, which suppressed the crack growth. This provides a possible explanation for the increased lifetime under cyclic leading conditions reported for ceramics by several investigators. While crack‐healing by high‐temperature annealing was found to greatly reduce the subsequent static fatigue crack growth rate, it had only a modest effecf on cyclic fatigue and none at high frequencies.