窒化ケイ素の泥しょう鋳込成形と焼結体の機械的特性 (第4報)

焼結助剤組成と焼結条件

抄録

The effects of compositions of Al₂O₃-Y₂O₃ sintering additives and sintering conditions on the mechanical properties were studied to determine the fabrication conditions of silicon nitride via slip casting. Slurries containing 67wt% solids (92wt%Si₃N₄ and 8wt%Al₂O₃-Y₂O₃), 33wt% distilled water and 0.01wt% deflocculant (polyacrylic ammonium) were prepared. After the forming by vacuum filtration using a porous polymer resin mold, samples were adequately dried and sintered in the temperature range from 1775 to 1825°C at 0.9MPa of N₂ pressure. High-density sintered bodies (3.16-3.25g/cm³) were obtained. The density tended to increase with raising temperature for a short sintering period (4h), while, decrease with raising temperature for a long sintering period (10h). Under the present preparation conditions, flexural strength maxima were observed at 3wt%Al₂O₃-5wt%Y₂O₃. A sample sintered at 1775°C for 10h showed an average flexural strength of 1138MPa and a Weibull modulus of 17.3. A composition of 3wt%Al₂O₃-5wt%Y₂O₃, that ratio corresponds to the liquid phase compositions at the lowest temperature in the system Al₂O₃-Y₂O₃-SiO₂, was favorable to obtain silicon nitride ceramics with high-strength at room temperature.