Crack-healing behavior of Si3N4/SiC composite under stress and low oxygen pressure

The crack-healing behavior of Si3N4/SiC composite under constant stress and low oxygen partial pressure was investigated. A semi-elliptical surface crack with a length of about 100 μm was introduced at the center of the tensile surface by the indentation method. The specimens were crack-healed at 1200 °C for 5 h under tensile stress (σapp. = 200–300 MPa) and under low oxygen partial pressure and air (PO2=50–21 000 PaPO2=50–21 000 Pa). The threshold constant stress for crack-healing was defined as 200 MPa in oxygen partial pressure over 500 Pa. The bending strengths of crack-healed specimens under tensile stress in PO2≥500 PaPO2≥500 Pa showed almost the same value as a healed smooth specimen, and most specimens fractured outside the crack-healed zone. From these results, we conclude that crack-healing can be achieved under stress in low oxygen pressure and can lengthen lifetime and increase reliability in Si3N4/SiC composite ceramic.