Development of new heat-resistant structural composite materials by MGC bulk and fiber crystals

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In this study, we investigated Melt Growth Composite (MGC) materials which can be used as structural materials at high temperature region around 1500℃ in air atmosphere. We established crystal growth method of MGC materials. We applied shape-control technique and achieved to fabricate fiber, plate and rod-shaped MGC materials. We studied several systems of MGC crystals and discovered highest strength in Y_3Al_5O_<12>(YAG)/AL_2O_3(sapphire)/ZrO_2(zirconia) ternary system.1. Establishment of crystal growth method of MGC materialsTo develop a thermally stable reinforcement materials which can be used at 1700℃, we investigated the conditions for stable growth of high quality, homogeneous eutectics crystals with controlled microstructure. By modifying the micro-pulling-down method with crucible, hot zone etc., we have established a new crystal growth technique for the eutectic crystals. We have clarified the relative orientations and method to control the microstructure of the eutectic comp … More onents of YAG and sapphire, by TEM electron diffraction analysis.2. Shaped crystal growthThe meniscus was well controlled by the end shape of the crucible, and we found a strong relation between meniscus and shape of grown crystals. Based on this observation, we achieved growing bulk eutectic crystals up to 5mmφ in diameter, plate crystals up to 10mm width, fiber crystals around 150μm in diameter. This crystal shape control technique can be applied for various field of related industry.3. Strength in high temperatureWe investigated several eutectic systems to search for the material which has higher strength than sapphire/YAG binary system. Among these, sapphire/YAG/zirconia ternary system showed highest strength. We tested tensile strength at room temperature in air atmosphere and at 1500℃ in Ar, and measured fundamental physical properties of the grown crystals such as thermal expansion coefficient etc. Tensile strengths reached 1730MPa at room temperature and 970MPa at 1200℃ in Ar atmosphere which is highest value in the world. Less