Static and cyclic fatigue behaviour of crack-healed Si3N4/SiC composite ceramics

Si3N4/SiC composite ceramics were sintered in order to investigate their fatigue strength behavior after crack healing, Y2O3 and Al2O3 power was added as sintering additives to enhance itʹs sintering property. Three-point bending specimen (sized 3×4×40 mm) was hewed out according to JIS standard from sintered compact obtained. About 100 or 200 μm semi-circular surface cracks were made on the center of the tension surface of the three-point bending specimen using Vickers indenter. After the crack-healing processing of 1200 and 1300°C, 1 h, in air, cyclic and static fatigue strength behavior of these crack-healed specimen were determined systematically at room temperature and high temperature of 800, 1000, 1200 and 1300°C. The results show that Si3N4/SiC composite ceramics possess remarkable crack-healing ability, and crack-healed specimens showed similar cyclic and static fatigue strength behavior as smooth specimens at high temperature, not only at room temperature. Crack-healed zones had sufficient fatigue strength even though at high temperature environment, and most fractures occurred outside the pre-cracked zone in those crack-healed specimens.