High‐Temperature Properties of Mixed α′/β′‐SiAlON Materials

The mechanical behavior of mixed α′/β′‐SiAlON materials was studied at elevated temperatures. Two different α′/β′‐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‐YN3AlN plane (α′‐SiAlON plane) were prepared using three different raw‐material mixtures. Six different materials were obtained with significantly lower values in α′‐SiAlON than expected. The high‐temperature properties of the materials studied were influenced strongly by the chemical composition (α′ content and grain‐boundary phase) of the SiAlONs. A high content of α′‐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 α′/β′‐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.