Effect of Phase Stability on the Microstructure Development of α-SiAlON Ceramics

Abstract

Alpha-SiAlON ceramics having various compositions and modifying cations were investigated with respect to their phase stability, transformation kinetics. and resulting microstructures. Each composition was heat treated at 150<TEX>$0^{\circ}C$</TEX> for 1h and measured the <TEX>$\alpha$</TEX>-SiAlON transformation. The phase-boundary composition in the single-phase <TEX>$\alpha$</TEX>-SiAlON region showed sluggish transformation from <TEX>$\alpha$</TEX>-<TEX>$Si_3N_4$</TEX> to <TEX>$\alpha$</TEX>-SiAlON compared to the phase-center composition in the diagram. Using the different rare earth modifying cations, dependence of transformation kinetics on the phase stability in a fixed composition was also explained. By changing size of the stable u-phase region with exchanging cations, systematic change in transformation was observed. Transformation rate of <TEX>$\alpha$</TEX>-SiAlON at low temperature has an important role on controlling the final microstructure. Less transformation gives more chances to develop elongated grain in the microstructure.