POTENTIAL USE OF MULLITE-SiC WHISKERS-SiC PARTICLES MULTI-COMPOSITE AS HIGH TEMPERATURE SPRINGS

Mullite has high fracture strength at high temperature, excellent resistance to heat, corrosion and oxidation as well as low Young's modulus. Thus, mullite is well suited for cushions and springs used at high temperatures. However, the low fracture toughness and reliability of mullite prevents use in these applications. If the reliability of mullite is improved through self-crack-healing ability, the use of mullite would be possible in these applications. in this study, mullite/SiC particle/SiC whisker multi-composites with improved fracture toughness and excellent self-crack-healing ability where the crack-healed part is stronger than the base materials were developed. Fracture strength and Young's modulus of mullite/15vol% SiC whiskers/10 vol% SiC particles multi-composite were found to be 750 MPa and 272 GPa, respectively. The maximum strain of the composite was evaluated to be 0.79 %. The value is almost 2 times larger than the monolithic mullite. The mullite multi-composite has 2.2 times larger fracture toughness of monolithic mullite. Moreover, mullite/15vol% SiC whiskers/10 vol% SiC particles multi-composite can completely heal a pre-crack of 100 mu m in surface length by exposure for 2 h in air at 1573 K. The crack-healed part was also found to be stronger than the base materials up to 1573 K.