Effect of solidification path on the microstructure of Al ₂O ₃-Y ₂O ₃-ZrO ₂ ternary oxide eutectic ceramic system

The solidification path of the Al ₂O ₃-Y ₂O ₃-ZrO ₂ ternary oxide eutectic composite ceramic is determined by a high temperature DTA and laser floating zone (LFZ) directional solidification method to investigate the effect of solidification path on the microstructure of the ternary oxide. The DTA and microstructure analyses show that the YAG or Al ₂O ₃ tends to form as primary phase under the unconstrained solidification conditions, and then the system enters ternary eutectic solidification during cooling from 1950°C at rate of 20°C/min. The as-solidified composite ceramic shows a divorced irregular eutectic structure consisting of Al ₂O ₃, YAG and ZrO ₂ phases with a random distribution. The primary phases are however completely restrained at the directional solidification conditions with high temperature gradient, and the ternary composite by LFZ presents well coupled eutectic growth with ultra-fine microstructure and directional array. Furthermore, the eutectic transformation and growth mechanism of the composite ceramic under different solidification conditions are discussed.