Crack-Healing Behavior of Structural Ceramics under Constant and Cyclic Stress at Elevated Temperature

Three types of structural ceramics, Al2O3/SiC, mullite/SiC and Si3N4/SiC having excellent crack-healing ability were sintered. A semi-elliptical surface crack of 75-110μm in surface length was made on each specimen with a Vickers indenter. The basic crack-healing behavior was studied systematically on Al2O3/SiC as a function of crack-healing temperature and time. Three point bending tests were carried out to investigate the strength of crack-healed samples. The specimens containing the semi-elliptical surface crack were healed under static or cyclic bending stress on mullite/SiC and Si3N4/SiC. It was shown that a crack could be healed completely either under a static or a cyclic stress. The competition between self crack-healing rate (SCHR) and crack growth rate (CGR=da/dt) determines the crack-healing behavior under stress: (i) In case of SCHR>CGR, a crack can be healed completely even under stress and recover of strength is complete. (ii) In case of SCHR≅CGR, a crack cannot be healed completely and recover of strength is insufficient. (iii) In case of SCHR