Crack-healing behaviour and resultant high-temperature fatigue strength of machined Si3N4/SiC composite ceramic

The crack‐healing behaviour of machining cracks in Si₃N₄/20 wt% SiC composite was investigated. The machining cracks were introduced by a heavy machining process, during the creation of a semicircular groove. The machined specimens were healed at various temperatures and times in air. The optimized crack‐healing condition of the machined specimens was found to be a temperature of 1673 K and a time of 10 h. The specimens healed by this condition exhibited almost the same strength as the smooth specimens healed. Moreover, the bending strengths and the fatigue limits of the machined specimens healed were systematically investigated at temperatures from room temperature to 1673 K. The machined specimens healed at the optimized condition exhibited an almost constant bending strength (～700 MPa) up to 1673 K. Also, the specimens exhibited considerably high cyclic and static fatigue limits at temperatures from 1073 to 1573 K. These results demonstrated that the crack‐healing could be an effective method for improving the structural integrity and reducing machining costs of the Si₃N₄/SiC composite ceramic.