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Silicon carbide particles embedded in ceramic matrices give rise to self-healing function in the structural ceramics operated at high temperature in air. This feature is taken advantage of to enhance life time of the ceramic components with high mechanical reliability. Ceramics are well-known to tend to have brittle fracture that usually occurs in a rapid and catastrophic manner. Brittle fracture is usually caused by the stress concentration at the tip of the flaws. For brittle fracture under pure mode I loading, under which crack is subjected to opening, the fracture criterion is that the stress intensity factor, KI, is equal to the fracture toughness, KIC. Since the value of KI is determined from the flaw size and the geometry between flaw and loading, one can understand that the fracture strength of ceramic components is not an intrinsic strength but is determined from fracture toughness and flaw size. Especially surface cracks are the most severe flaws because surface cracks lead to the highest stress concentration. If surface cracks are introduced during service, e.g., crash or thermal shock, the strength of ceramic components decreases significantly. The behaviour leads to low mechanical reliability of ceramic components. The ceramic composites containing silicon carbide particles can heal surface cracks by themselves, as shown in Fig. 1 (Nakao et al., 2010, Ando et al., 2004). Surface cracking allows the silicon carbide particles on the crack walls to contact the oxygen in the surrounding atmosphere. If the components operated at high temperature, the contact would cause the oxidation of silicon carbide. The oxidation includes almost two times volume expansion of the condensed phases and the huge exothermic heat. Due to the volume expansion, the space between the crack walls can be completely filled with the formed oxide. Furthermore, the reaction heat leads to strong bonding at the interface between the matrix and the formed oxide. As a result, the self-healing induced by the oxidation of the embedded silicon carbide particles can recover the degraded strength completely and can enhance the life time of the ceramic components with high mechanical reliability. 11

Effect of Self-Healing on Fatigue Behavior of Structural Ceramics and Influence Factors on Fatigue Strength of Healed Ceramics