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The mechanical behavior of mixed ␣/␤-SiAlON materials was studied at elevated temperatures. Two different ␣/␤-SiAlON compositions along the Si 3 N 4 -Y 2 O 3 ؒ9AlN composition line in the Si 3 N 4 -Al 2 O 3 ؒAlN-YNؒ3AlN plane (␣-SiAlON plane) were prepared using three different raw-material mixtures. Six different materials were obtained with significantly lower values in ␣-SiAlON than expected. The high-temperature properties of the materials studied were influenced strongly by the chemical composition (␣ content and grain-boundary phase) of the SiAlONs. A high content of ␣-SiAlON was beneficial in terms of creep behavior of the materials. The same materials, however, were characterized by a considerably degradated fracture behavior at elevated temperatures in air because of a crack-growth process enhanced by the poor oxidation resistance of these materials. It was concluded that, despite some superior features of the materials studied, a long-term application of mixed ␣/␤-SiAlON materials at 1400°C in air is problematical. A combination of all properties required for such applications was not observed. For that reason, it is suggested that the real high-temperature potential of these materials in air should be limited to temperatures <1300°C.

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