Coupled Growth Zone of the Al<SUB>2</SUB>O<SUB>3</SUB>-YAG Eutectic System in the Undercooled Melt

Coupled growth in the undercooled solidification of the Al2O3-YAG eutectic system was investigated for specimens in a composition range of 17.0 to 20.0 mol%Y2O3 by using an optical DTA apparatus. Growth rate of the eutectic interface was estimated from solidification time and specimen size and the possible growth rate was from 10−5 to 10−4 m/s. The relationship between the eutectic spacing and growth rate obeys λ2V=const in the experimental condition. Specimens with compositions of 1 mol% less or more than the eutectic composition always exhibited primary Al2O3 or YAG phases. In contrast, the specimens with the eutectic composition were completely covered with the eutectic structure. The coupled growth was confirmed in the Al2O3-YAG system, but the composition range of coupled growth was 1 mol% at most. The growth rate from 10−5 to 10−4 m/s did not affect the coupled growth zone.