Font Size: 

For new approach to improve reliability of structural ceramics, the present authors havedeveloped Si 3 N 4 and mullite ceramics having self-crack-healing ability. In this study,mechanical properties at high temperature and crack-healing ability of alumina / SiC particlescomposite, alumina / SiC whiskers composite, and alumina / SiC particles / Y 2 O 3 compositeswere investigated. Excellent crack-healing ability so that fracture strength reduced bycracking is recovered above that of as-received specimen was endowed for the composites.Fracture strength of alumina / SiC particles composite and alumina / SiC particles / Y 2 O 3composites were 1.8 and 3.0 times larger than the value of monolithic alumina, respectively,because alumina grains after sintering were downsized. Moreover, fracture strength ofalumina / SiC whiskers composite was improved up to 2.5 times larger than the value ofmonolithic alumina by bridging effect of SiC whiskers. The heat-resistance limit temperaturefor strength, T HR , of the crack-healed alumina / SiC particles composite was improved to1300oC from 900oC by nano-compositing. Fracture toughness of alumina / SiC whiskerscomposite was found to be 1.6 times higher than that of monolithic alumina. Bridging andpull-out effects by SiC whiskers improved the fracture toughness.1. IntroductionStructural ceramics such as alumina, mullite and silicon nitride have excellent heat, corrosionand wear resistance. However, fracture toughness is low. This low reliability has, thus,limited their applications. Many investigators tried to improve the fracture toughness ofstructural ceramics by admixing with whisker and fiber. On the other viewpoint to improvereliability of structural ceramics, the present authors [1-12] have proposed endowing thecrack-healing ability by using oxidation of SiC. When ceramics admixed with SiC are kept inair at high temperature, SiC located on the crack surface reacts with O 2 in air and then crackis completely restored by the products and the heat of the reaction. Moreover, the restoredpart is mechanically stronger than the other parts. If the above mechanism so called as crackhealingis used on structural components in engineering use, great benefits can be anticipatedimprovement in reliability as well as a decrease in machining and polishing costs of ceramicselements.In the previous studies [1-3, 10], the present authors succeeded endowing the excellent crackhealingability to mullite by admixing with 15 mass% SiC particles. The fracture strength ofthe mullite composite was reduced almost quarter by cracking, and recovered completely bycrack-healing at 1300oC for 1 h. Moreover, it was found that mullite admixed with 15 vol%