Densification behaviors and high-temperature characteristics of Si3N4 sintered bodies using Al2O3–Yb2O3 additives

The densification behaviors (include α–β transformation) and high-temperature characteristics (especially oxidation resistance and high-temperature strength properties) of Si3N4 sintered bodies using Al2O3–Yb2O3 based sintering additive are investigated. ication and α–β transformation behaviors were investigated by varying the compositions of Al2O3–Yb2O3 additives. In terms of the influence of the Y2O3/Al2O3 ratio on densification behavior, a greater Yb2O3/Al2O3 ratio tends to inhibit densification. The α–β transformation tended to be delayed in sintered bodies with a small additive amount of 3.4 mass%. Compared with the transformation behaviors of the sintered bodies using Al2O3–Y2O3 additives, those using Al2O3–Yb2O3 additives exhibited a narrower temperature zone for α–β transformation, which attributed to the finer structure for the sintered body using Al2O3–Yb2O3 additives. This is affected by the difference in solubility of Si3N4 in the two kinds of glass phase. oom temperature strength of 900–1000 MPa was obtained for sintered bodies with a 10.0 mass% addition of additives, and this is considered to be due to the finer micro-structure. Precipitation of a Yb4Si2N2O7 phase at the grain boundary glass phase, as induced by crystallization processing, enables the improvement of 1300 °C strength to about 650–720 MPa. Crystallization processing resulted in a 30% reduction in the amount of weight change during oxidation (from 3.42 to 2.46 mg/cm2), demonstrating the effectiveness in improving oxidation resistance.