Crack Healing of Machining Cracks Introduced by Wheel Grinding and Resultant High-Temperature Mechanical Properties in a Si3N4/SiC Composite

The crack-healing behavior of machining cracks in a Si3N4/SiC composite containing Y2O3 and Al2O3 as a sintering additive was investigated. The machining cracks were introduced by a wheel grinding process, which is the most common method for finishing ceramic components. A semicircular groove was made at the center of small bending specimens by the machining. The machined specimens were healed at various temperatures and times in air. The optimized crack-healing condition of the machined specimen was found to be a temperature of 1300°C and a time of 1 h. The specimens healed by this condition exhibited almost the same strength as the smooth specimens that underwent the healing process. Moreover, the bending strength and fatigue limit of the machined and healed specimens were systematically investigated at temperatures ranging from room temperature to 1300°C. The heat-resistance temperature has been determined to be approximately 1000°C. Also, the specimens exhibited high static and cyclic fatigue limits at temperatures of 800° and 1000°C. These results demonstrate that crack healing could be an effective method for improving the structural integrity and reducing the manufacturing costs of a Si3N4/SiC composite ceramic.