A preliminary study on crack healing behaviour of Si3N4/SiC composite ceramics

Ceramic (Si3N4/SiC) composites have been produced by sintering. From the sintered block, three point bend specimens were cut out. A semi-circular crack was made on the centre of the tension surface of the test specimen with the aid of a Vicker's indenter. The diameter of the semi-circular crack was about 60-70 mu m. The specimens were subsequently heat treated at 1300 degrees C for Ih in vacuum, nitrogen or air. The bending strength was measured at room temperature, 800 and 1000 degrees C. The specimens heat treated in air recovered considerably their bending strength at 1000 degrees C, several specimens failed at a location different from the healed crack and their average strength showed the same value of that for smooth specimens. From these results; it is concluded that the recovery in bending strength of a cracked specimen war caused by crack healing.