Effect of Si_3N_4 Starting Powders on Formation of Elongated Ca-α-Sialon Grains

Two kinds of Si3N4 starting powders with different a/B ratios were used to prepare Ca-α-Sialon with the composition Ca1.8Si6.6A15.4O1.8N14.2 by pressureless sintering. The densificationprocess, reaction sequence and microstructure of the corresponding materials were studied by XRDanalysis and SEM observation. Elongated a-Sialon grains were observed in the materials sinteredwith either St3N4 starting powders. On the other hand, Si_3N_4 starting powders with high Bphase content resulted in poorer densification during sintering and the temperature for completedissolution of P-Si_3N_4 was 100℃ higher than that for α-Si_3N_4. The higher the content of B phasein the starting powders, the fewer nucleation sites there were, and the coarser a-Sialon grains were.A broad size distribution of the St3N4 starting powders led to the inhomogeneity of a-Sialon grainsizes.