Si3N4/SiC composite containing Y2O3 as sintering additive was hot-pressed to examine their crack-healing behavior as a function of oxygen partial pressure (pO2 = 50–21,000Pa). A semi-elliptical surface crack with length of about 100μm was introduced on the center of tensile surface by the indentation method. These specimens were healed at various temperatures and times using tube furnace. After the crack-healing process, the bending strength of each specimen was measured at room temperature and at high temperatures of 800-1,400°C. Even under pO2 = 50Pa, the cracks were completely healed by heat treatment at 1,300°C for 10h. Bending strengths of the crack-healed specimens exhibited almost the same strength as the smooth specimens healed. Moreover, the specimens exhibited an almost constant bending strength (∼800MPa) up to 1,400°C.
