HIGH TEMPERATURE CHARACTERISTICS OF MELT GROWTH COMPOSITE

摘要

Much attention has been paid to unidirectionally solidified ceramic composites as a candidate for a high-temperature structural material. We have recently developed eutectic composites, which are named as Melt Growth Composites (MGCs). The Al{sub}2O{sub}3/YAG binary MGC has a novel microstructure, in which continuous networks of single-crystal Al{sub}2O{sub}3 phases and single-crystal YAG phases interpenetrate without grain boundaries. The binary MGC fabricated is thermally stable and has the following properties: 1) the flexural strength at room temperature can be maintained up to 2073 K (just below its melting point), 2) the compressive creep strength at 1873 K and a strain rate of 10{sup}(-4)/sec is approximately 13 times higher than that of the sintered composite, and 3) it shows neither weight gain nor grain growth, even upon heating at 1973 K in an air atmosphere for 1000 hours. In addition, we have recently developed a new Al{sub}2O{sub}3/YAG/ZrO{sub}2 ternary MGC. The present ternary MGC displays superior high-temperature strength characteristics. The flexural strength increases progressively in the range 650-800 MPa with a rise of temperatures from room temperature up to 1873 K. These excellent high-temperature characteristics are attributed to MGC's unique microstructure consisting of single crystal phases interpenetrated with each other and their interfaces. The binary and ternary MGCs are expected to be widely used in mechanical engineering at very high temperatures in the future.