HIGH-TEMPERATURE STRENGTH AND THERMAL-STABILITY OF A UNIDIRECTIONALLYSOLIDIFIED AL2O3 YAG EUTECTIC COMPOSITE/

A unidirectional solidification method was investigated to manufacture Al2O3/YAG eutectic composites with high-temperature resistance that w ould make them usable at very high temperatures. We were successful in manufacturing a single-crystal Al2O3/single-crystal YAG eutectic comp osite with a dimension of 40 mm in diameter and 70 mm in length contai ning no colonies or pores. This composite also displayed excellent hig h-temperature strength characteristics. The flexural strength was in t he range 350 similar to 400 MPa from room temperature up to 2073 K (ju st below its melting point of about 2100 K) with no apparent temperatu re dependence. During tensile tests above 1923 K, the eutectic composi te showed evidence of plastic deformation occurring by dislocation mot ion, and a yield phenomenon similar to many metals was observed. In ad dition, the microstructure of the composite was extremely stable: afte r 1000 h of heat treatment at 1973 K in an air atmosphere there was no growth. The above superior high-temperature characteristics are cause d by such factors as the eutectic composite having a single-crystal Al 2O3/single-crystal YAG structure, the formation of a compatible interf ace with no amorphous phase and thermal stability, and the combined ef fect of a YAG phase with superior high-temperature characteristics. (C ) 1998 Chapman & Hall.