In order to develop stable composite materials in air atmosphere above 1673 K, fabrication of unidirectional solidification of Al2O3/Y2O3 mixed powders (82/18 mol ratio) was carried out in 10−5 mmHg vacuum at the 5 mm/h down speed using advanced alloy crystalline structure controlling equipments at Japan Ultra-high Temperature Materials Research Center. The microstructures of the unidirectional solidified eutectic composites were composed of single crystal (110) Al2O3 and single crystal (420) YAG containing no colony and porosity. No temperature dependence of flexural strength of the composites from room temperature to 1973 K was observed and the flexural strength is 360∼500 MPa. It is found that the composites have superior creep resistance at 1873∼1973 K, oxidation-resistance and thermal stability at 1973 K for 50 h in air atmosphere.
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Waku et al. (1995) studied this question.