Effect of SiC Shape on The Crack-Healing Mechanism of Alumina/SiC Composite
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Effect of SiC Shape on The Crack-Healing Mechanism of Alumina/SiC Composite Wataru Nakao, Toshio Osada, Kazuya Yamane, Masahiro Yokouchi1, Koji Takahashi and Kotoji Ando Department of Safety & Energy Engineering, Yokohama National University, 79-5, Tokiwadai Hodogaya-ku, Yokohama, 240-8501, Japan 1 Kanagawa Industrial Technology Research Institute, 705-1 Imaizumi, Ebina, 243-0435, Japan
ABSTRACT Crack-healing of structural ceramics is a most valuable technique to overcome their weak point such as surface cracks. Crack-healing ability appeared by admixing SiC to ceramics, because this function is to use the oxidation of SiC. Endowment of crack-healing ability as well as improvement in fracture toughness was expected to be achieved by compositing SiC whiskers. For this purpose, alumina / 30 vol% SiC whiskers and alumina/ 20vol% SiC whiskers/ 10 vol% SiC particles multi-composites were developed. Crack-healing ability and fracture toughness of these composites were investigated. Alumina/ 20 vol% SiC whiskers/ 10 vol% SiC particles multi-composite and alumina/ 30vol% SiC whiskers composite were found to have 1.43 times and 1.65 times higher fracture toughness than monolithic alumina, respectively. From the results of the strength recovery by crack-healing, alumina/ 20 vol% SiC whiskers/ 10 vol% SiC particles multi-composite and alumina / 30vol% SiC whiskers composite were found to be able to heal the pre-crack below 250 μm and 200 μm in surface length, respectively. In spite of the same SiC content, SiC particles and SiC whiskers multi-compositing enlarged the limit crack size to be able to crack-heal. On the other hand, increasing SiC whiskers content enhanced strength recovery of the specimen with the large crack above limit crack-size.
INTRODUCTION Self-crack-healing ability is one of valuable functions for structural ceramics. Ceramics are well known to have low fracture toughness. Thus, cracks initiate easily and fracture strength is significantly reduced by cracking. If cracks and flows acting as fracture initiation are completely healed, the reliability of structural ceramics will be greatly improved. The self-crack-healing ability proposed by the present authors [1-9] used the oxidation of SiC as expressed by Eq. (1), SiC + 3/2O2 = SiO2 +CO
(1).
As ceramics admixed with SiC powders are kept in air at high temperature, SiC located on crack surface reacts with O2 in air. As a result, cracks are completely healed by the products and the heat of the reaction. Moreover, the crack-healed part is mechanically stronger than the other parts. Further improvement of reliability can be anticipated by SiC whiskers compositing, as it is possible not only to only to endow with self-crack-healing ability but also to improve fracture
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toughness. In the previous study [8, 9], fracture toughness and crack-healing ability of alumina/ 20 vol% SiC whiskers composite have been investigated by the present authors investigated. The fracture toughness of alumina/ 20 vol% SiC whiskers composite has been
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