Improved densification by nano-sized sintering aids for Si₃N₄

The densification of Si₃N₄ with nano-sized sintering aids that were in situ incorporated by a combustion process was studied in comparison with that of sintering aids mixed by ball milling. The combustion process directly produces amorphous and nano-sized Y–Al oxides within the Si₃N₄ powder. X-ray diffraction results indicate that amorphous Y–Al oxides begin to crystallize into Y₃Al₅O₁₂ at about 600 °C. Additionally the nano-sized sintering aids are more homogeneously distributed and thereby promote the formation of eutectic melts at lower temperatures during liquid-phase sintering. Therefore, the densification process of Si₃N₄ during liquid-phase sintering is strongly accelerated. The microstructure of as-sintered parts from combusted powder seems more dense and homogeneous.