Influence of Sintering Aid on the Translucency of Spark Plasma-Sintered Silicon Nitride Ceramics

摘要

Single additives (Y_2O_3, MgO, and Al_2O_3) were used as sintering aid of Si_3N_4. The density, crystal phase, microstructure, transmittance, hardness, and fracture toughness of sintered Si_3N_4 were investigated. Highly densified sintered bodies were obtained in single Y_2O_3 and MgO systems, but not in single Al_2O_3 system. The XRD results indicated that sintered bodies were composed of β-Si_3N_4. The SEM images showed that all the sintered bodies had a fine-grained microstructure with an average diameter of 0.29-0.37 μm. The thickness of grain boundary was changed with additive content. The transmittance (7) and the wavelength (λ) followed the relationship of Tα exp (-λ~(2.3)) due to the light scattering. The transmittance was mainly influenced by the refractive index of additives and the thickness of grain boundary phase. The hardness and fracture toughness of sintered ceramics were 12.6-15.5 GPa and 6.2-7.2 MPam~(1/2), respectively.