Crack-healing behaviour of mullite/SiC/Y2O3 composites and its application to the structural integrity of machined components

High-strength mullite/SiC/Y2O3 composite ceramics with a great crack-healing ability were developed and subjected to three-point bending. A semicircular surface crack 100 μm in diameter was made in each specimen. Crack-healing behaviour was systematically studied as a function of crack-healing temperature and healing time, and the bending strength of the specimens crack-healed up to 1573 K was investigated. The effects of the crack-healing treatment on the structural integrity and reliability of machined components were studied systematically. Four main conclusions were drawn from the present study: (1) mullite/SiC/Y2O3 composite ceramics have the ability to heal after cracking from 1423 K to 1673 K in air, (2) the heat-resistance limit temperature for strength of the crack-healed specimen is ≅1473 K, while at 68% of the specimens fractured from outside the crack-healed zone in the tested-temperature range of 300–1573 K, (3) due to the crack-healing treatment, the strength of the machined specimen increased by 40–200%. Local fracture strength was assumed to recover completely, and the cracks formed by machining were healed completely, and (4) a large self-crack-healing ability is desirable for obtaining a higher structural integrity in ceramic components.