Growth and diameter control of Al₂O₃/Y₃Al₅O₁₂ eutectic fiber by micro-pulling-down method and its high temperature strength and thermal stability

We investigated the fiber growth of the oxide eutectic composites sapphire/Y₃Al₅O₁₂ (YAG) using the micro pulling down (μ-PD) method. Sapphire and YAG phases were crystalline. They form a continuous three-dimensional networking with some preferred orientation of the growth direction. We have succeeded in control the fiber diameter from 2 mm to 150 μm. The maximal length was about 500 mm. The scale of the microstructure was also controlled from 20 μm to 0.5 μm. The eutectic fibers have superior high-temperature strength properties around 1500 °C. In the tensile test at this temperature, these fibers showed remarkable (about 10%) plastic deformation occurring by dislocation motion. The microstructures of these eutectic fibers have a very high thermal stability. No grain growth was observed after even 75 hours heat treatment at 1500 °C in an air atmosphere.