High-temperature properties of mixed alpha-prime/beta-prime-SiAlON materials

The mechanical behavior of mixed alpha-prime/beta-prime-SiAlON materials was studied at elevated temperatures. Two different alpha-prime/beta-prime SiAlON compositions along the Si3N4n-Y2O3 9AlN composition line in the Si3N4-Al2O3 AlN-YN 3AlN plane were prepared using three different raw-material mixtures. Six different materials were obtained with significantly lower values in alpha-prime-SiAlON than expected. The high-temperature properties of the materials studied were influenced strongly by the chemical composition of the SiAlONs. A high content of alpha-prime-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 alpha-prime/beta-prime-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 less than 1300 C. (Author)