Preparation and characterization of Al₂O₃/Y ₃Al₅O₁₂/ZrO₂ ternary hypoeutectic in situ composites by laser rapid solidification

The directionally solidified oxide eutectic in situ composite is one of the most promising high-temperature structural materials in oxidizing environments. Pore-free rods and plates of ternary Al₂O₃/Y ₃Al₅O₁₂ (YAG)/ZrO₂ hypoeutectic in situ composites with hypoeutectic composition (71 mol % Al₂O ₃, 17 mol % Y₂O₃, and 12 mol % ZrO₂) are prepared rapidly by the laser zone remelting technique. The hypoeutectic growth and microstructure characteristic of grown crystals are studied using the scanning electron microscopy, x-ray diffraction, and energy dispersive spectroscopy, aiming to understand well the rapid solidification behavior of the ternary oxide system of Al₂O₃-Y₂O ₃-ZrO₂. The rapidly solidified Al₂O ₃/YAG/ZrO₂ hypoeutectic shows a refined, interpenetrating, and irregular lamellar structure with a reticular distribution of coarse Al₂O₃ and yttrium aluminum garnet (YAG) and smaller ZrO₂ phases. The fine ZrO₂ phases are partially embedded at the Al₂O₃/YAG interfaces. Moreover, the typical dendrite microstructure similar to the metallic solidification is also observed. The formation of two kinds of microstructures is mainly attributed to the rapid growth during the laser zone remelting and constitutional supercooling. The Al₂O₃ and YAG phases grow in a typical faceted manner, and the ZrO₂ phase presents a weak-faceted growth. The size of the interphase spacing obtained decreases rapidly in increasing the laser scanning rate. The fundamental investigations on the irregular growth mechanisms of the hypoeutectic are suggestive to the comprehension of the complex solidification behavior of the ternary oxide systems.