Crystallization of Zirconium Nitride in Silicon Nitride Ceramics with Nitrogen Pressures and Sintering Additives

摘要

We investigated grain boundary crystallization of gas-pressure-sintered silicon nitride with zirconia and magnesia as sintering aids. Cation compositions were mostly uniform throughout the specimen however, ZrO_2 was crystallized in the surface region, while ZrN in the inside. When the specimen was heat-treated at 1 atm nitrogen atmosphere, ZrO_2 in the surface region transformed to ZrN. The transformation, however, was suppressed when alumina was incorporated as an additional sintering aid. Based on these results, we propose a model describing the reaction among Si_3N_4, SiO_2, ZrO_2, ZrN and N_2. Observed microstructures and measured mechanical properties were consistent with the model.