Eutectic Composites in Al2O3-Y2O3 System Solidified by Horizontal Directed Crystallization Method

Al2O3-YAG eutectics bulk crystals have been obtained by the horizontal directional crystallization method under the total pressure of 1.3 x 10(5) Pa. Two approaches have been applied to reach the given morphology: (i) the first one consisted of the direct solidification of the melt of Al2O3 and Y2O3 to crystallize the Al2O3-YAG eutectics below 2000 degrees C, (ii) the second one included two stages, i.e., the crystallization of the metastable eutectic Al2O3-YAP overheated to 2000 degrees C followed by phase transformation from YAP to YAG at the evaluated temperature. The first approach resulted in the crystal with "Chinese script" morphology, which increased in the interphase segments with the lowering rate of crystallization. The morphology of the original Al2O3-YAP eutectic is tubular, but could be easily and quickly transformed into Al2O3-YAG "Chinese script" at 1700 degrees C keeping the dimensional structure of the Al2O3-YAP. The interphase segments in such eutectics were mostly fine among all samples produced and were equal to 1.7 mu m for the Al2O3 phase and 2.9 mu m for the YAG phase. As a result, it has been shown that the horizontal directional crystallization method is applicable to the production of eutectics of Al2O3-YAG with a controlled structure. Such eutectics can be used at high temperatures as construction materials and as optical media with high scattering features.