Microstructural morphology and irregular eutectic growth of directionally solidified Al2O3/YAG eutectic in situ composite
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陕西西安西北工业大学凝固技术国家重点实验室
Cite this article:
;. Microstructural morphology and irregular eutectic growth of directionally solidified Al2O3/YAG eutectic in situ composite. Acta Metall Sin, 2008, 44(4): 457-462 .
Abstract Directionally solidified Al2O3/Y3Al5O12 (YAG) eutectic in situ composite was prepared by the laser zone remelting technique. The eutectic morphology, phase composition, interface structure, microstructure evolution and phase precipitation rule were analyzed by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), energy disperse spectroscopy (EDS) and transmission electron microscopy (TEM). The irregular microstructure morphology was quantitatively characterized by fractal dimension. Further more, the irregular eutectic growth mechanism of the oxide eutectic was detailedly discussed. The results show that the directionally solidified Al2O3/YAG eutectic in situ composite only consists of homogeneously distributed Al2O3 and YAG phases with well matched interfaces. The two phases interweave each other and coupledly grow, showing a “Chinese script” structure. The YAG phase is the primary phase during solidification. The eutectic spacing is highly refined with increasing the laser scanning rate and the minimal spacing is down to 0.2um. At low laser scanning rate, the eutectic tends to show typical lamellar irregular eutectic structure and has evident fractal characteristic, whereas, when the laser scanning rate reaches a high value of 2000um/s, the cellular and dendritic structures appear and the fractal characteristic is weaken. The faceted/faceted eutectic growth derived from the large kinetic undercooling of laser rapid solidification and high entropies of fusion of eutectic phases is the most primary factor to determine the formation of the complexly irregular eutectic morphology.
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