Abstract
Changes of YAP-phase content and some properties by annealing the Si3N4-Al2O3-Y2O3-AlN ceramics have been studied. Annealing was performed at temperatures 1100-1500°C for 1-10h under vacuum. Above 1200°C, the YAP-phase content in Si3N4 ceramics decreases on annealing and the YAG-phase precipitates. The precipitation of YAG-phase increases the high temperature hardness and chemical resistance to a HF+HN3 solution. The YAP-phase seems to be easily etched by the HF+HNO3 solution and softened at high temperatures compared to YAG-phase.
