Morphology and microstructure of crystalline YAG-Al2O3 composites grown by the horizontal directional crystallization
Oleh Vovk, Yuriy Siryk, Sergiy Nizhankovskyi, Alexander Fedorov, Pavel Mateichenko
Abstract
The peculiarities of the horizontal directional crystallization of the melt (Y 3 Al 5 O 12 , 90 wt% and Al 2 O 3 10 wt%) were studied. The evolution of both the morphology of the ingot and the microstructure of the inclusions as a function of the rate of melt solidification was established. It was shown that the crystallization of the ingot begins with the growth of the YAG single crystal, which turns into the YAG cellular growth, with cells surrounded by the YAG-Al 2 O 3 eutectic. Cellular growth is replaced by dendritic YAG growth followed by spontaneous crystallization. The inclusions consist of eutectic YAG-Al 2 O 3 , which usually presented pores caused by the solidification of the eutectic in the confined volume. The morphological stability of the crystallization front is partially kept until dendritic growth occurs. Parts of the ingot with a dendritic structure can be an effective light-scattering medium that can be used as a host for luminescent ions in converters of solid-state light sources.