Effect of TiO2 addition on oxidation behavior of sintered bodies composed of Si3N4-Y2O3-Al2O3-AlN

The effect of TiO2 content on the oxidation of sintered bodies from the con ventional Si3N4-Y2O3-Al2O3-AlN system was investigated. Sintered specimens composed of Si3N4, Y2O3, Al2O3, and AlN, with a ratio of 100 : 5 : 3 : 3 wt % and containing TiO2 in the range of 0 to 5 wt% to Si3N4, were fabricated at 1775 degrees C for 4 h at 0.5 MPa of N-2. Oxidation at 1200 to 1400 degr ees C for a maximum of 100 h was performed in atmospheres of dry and wet ai r flows. The relation between weight gain and oxidation time was confirmed to obey the parabolic law. The activation energies decreased with TiO2 cont ent. In the phases present in the specimens oxidized at 1300 degrees C for 100 h in dry air, Y3Al5O12 and TiN, which had existed before oxidation, dis appeared. Alpha-cristobalite and Y2O3. 2TiO(2) (Y2T) appeared in their plac e and increased with increasing TiO2 content. In those oxidized at 1400 deg rees C, alpha -cristobalite was dominant and very small amounts of Y2O3. 2S iO(2) and Y2T were contained. There was a tendency for more alpha -cristoba lite to form in oxidation in wet air than in dry air. Therefore, moisture w as confirmed to affect the crystallization of SiO2 formed during oxidation. Judging from the lower activation energy, the crystallization, and the por es formation, we concluded that the addition of TiO2 decreases oxidation re sistance. (C) 2000 Kluwer Academic Publishers.