Elimination of Grain Boundary Glass in α-Sialon by Adding Aluminium

The elimination of residual glass in hot-pressed Y-α-SiAlON was demonstrated by varying the nitride composition. This was readily achieved by adding excess aluminium nitride (AlN), while the addition of excess Si3N4 had little effect. The amount of excess AlN required for this purpose increased with increasing Al and O content in α-SiAlON, and was higher if α-SiAlON contained larger interstitial cations. These results were explained by the thermodynamics of α-SiAlON precipitation. The elimination of liquid also led to suppressed grain growth, refined microstructure, and improved oxidation resistance. Grain coarsening by post-sintering annealing was required to obtain high fracture toughness.