Solidification of Al_2O_3-YAG eutectic composites with off-metastable eutectic composition from undercooled melt produced by melting Al_2O_3-YAP eutectics

摘要

It has been reported that solidification of the Al_2O_3-YAG equilibrium eutectic structure follows melting of the Al_2O_3-YAP metastable eutectic structure. Since the exothermic heat due to solidification was consumed by the endothermic heat due to melting, a fine and uniform eutectic structure was obtained. However, the composition of the Al_2O_3-YAG eutectic structure is restricted to the metastable eutectic composition. In this paper, Al_2O_3-YAG eutectic compacts with an off-metastable eutectic composition were prepared by the addition of Al_2O_3 particles to Al_2O_3-YAP eutectic particles with diameters less than 20μm. In compositions ranging from 18.5 mol%Y_2O_3 to 13.5 mol%Y_2O_3, dense Al_2O_3-YAG eutectic compacts were formed without any Al_2O_3 segregation. The flexural strength and the fracture toughness remained almost unchanged with the increase in the Al_2O_3 phase. The addition of Al_2O_3 particles to the Al_2O_3-YAP eutectic particles enabled the matrix phase to change from the YAG phase to the Al_2O_3 phase.