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The heat-resistant limit of structural ceramics is 1273K ~ 1773K, which is greatly superior to that of metallic material. Structural ceramics are a candidate element for high-temperature apparatuses such as gas-turbines and fusion reactors. However, the fracture toughness of ceramics is fairly low compared with metallic material, and the following problems have occurred. (1) Cracks occur by the usual machining process (grinding, polish, etc.), lowering the reliability. In order to prevent this, precise polishing is required in the final stage, which is time-consuming, and there are also problems with fabrication efficiency and fabrication cost (2) Crack sizes of about 10 ~ 30 μm in depth affect the reliability. The nondestructiveinspection technology for detecting cracks of 10 ~ 30 μm is underdeveloped. Therefore, the reliability of major parts is low. (3) There is a possibility that a crack will occur in the components while they are being used at higher temperatures, by whatever cause. When a crack occurs, the reliability is greatly lowered. The options for resolving these problems are as follows. (a) Improve the fracture toughness of the material by such means as microstructure control and fiber reinforcement. (b) Conduct a nondestructive inspection before use, and detect and repair any dangerous cracks found. (c) Conduct a proof test to prevent use of a low reliability member. (d) Induce a selfcrack-healing ability, so that all dangers cracks can be healed. There are world-wide active investigations of options (a) to (c). In this chapter, special attention is paid to method (d), the self–crack-healing ability of structural ceramics. There are three advantages to using a material that can heal surface cracks. (A) If the selfhealing of the surface crack which exists is carried out after an efficient machine operation is performed, then there is a great advantage in fabrication efficiency and fabrication cost. (B) Since all surface cracks are healed, reliability improves greatly. (C) It is advantageous if a crack which occurs while in service can be healed and full recovery of strength achieved. From the above ideas, the self-crack-healing behaviors of ceramics were investigated by Ando and co-worker. Silicon nitride (Ando et al, 1998; Yao et al., 2001), alumina (Takahashi et al., 2003; Ando et al., 2004; Nakao et al., 2005a), and mullite (Chu et al., 1995; Nakao et al., 2006) , SiC (Kim Y.W. et al., 2003; Lee et al., 2005a) and ZrO2 (Houjou et al., 2010), with the self–crack-healing ability have been developed. In the following section, an outline is given of the crack-healing behavior of ceramics.

Crack-Healing Ability of Structural Ceramics and Methodology to Guarantee the Reliability of Ceramic Components