In order to develop stable composite materials in an air atmosphere above 1773 K, unidirectionally solidified Al2O3/Er3Al5O12 eutectic composites were fabricated by using the Bridgman-type equipment at the Japan Ultra-high Temperature Materials Research Center. Composites with dimensions of 40 mm in diameter by 70 mm in length consisted of single-crystal-like Al2O3 and single-crystal Er3Al5O12 without colonies or pores. The flexural strength of the composite is temperature independent from room temperature up to 2073 K (just below its melting point of about 2130 K). It was found also that the microstructure of the present composite has excellent thermal stability at 1973 K in an air atmosphere. The above superior high-temperature characteristics are due to a microstructure consisting of three-dimensionally continuous and complexly entangled single-crystal-like Al2O3 and single-crystal Er3Al5O12 phases, the formation of interfaces with no amorphous phases and comparatively good coherence.
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Nakagawa et al. (2000) studied this question.