Sintering behavior of hot-pressed Ca-α-sialon ceramics

On the basis of phase relationships in the CaSi-Al-O-N system, a Ca-alpha-sialon ceramic was synthesized using the hot-pressing technique. The reaction sequences and densifications of the Ca-alpha-sialon vs, firing temperatures have been characterized in detail. The present experiments reveal a reaction sequence as follows: at 1250 degrees C the reactant mixture started to soften, at 1300 degrees C a gehlenite phase was produced, at 1500 degrees C the gehlenite phase was resolved into a Liquid phase and a Ca-alpha-sialon started to form, and at 1600 degrees C the formation of Ca-alpha-sialon was complete. The product was stable and almost entirely single phase Ca-alpha-sialon. Accompanying to the above sequences, densification also proceeded via a liquid-phase sintering, particle rearrangement, solution-reprecipitation, and grain growth process. In the final microstructure elongated grains of Ca-alpha-sialon were obtained, improving the fracture toughness of this Ca-alpha-sialon ceramic.