Effect of Heat Treatment on Thermal Conductivity of Silicon Nitride Ceramics

抄録

Dense Si₃N₄ ceramics are not mono-phase materials because their additives may be remained as an amorphous or partially crystallized grain-boundary-phase. The grain boundary phase has several positive effects on production of high strength and high fracture toughness ceramics. On the other hand, the grain boundary phase will generally reduce high temperature mechanical properties and thermal conductivity. An Y₂O₃-Al₂O₃ system is one of the most popular additives for densification of Si₃N₄ because low temperature for sintering and the resulted ceramics show excellent mechanical properties. But Al₂O₃ will form SiAlON phase which has low thermal conductivity. The additives react with SiO₂ as other substance in a Si₃N₄ raw powder and change to glassy phase between Si₃N₄ grains during sintering. In this study, Si₃N₄ was gas-pressure sintered with Y₂O₃- SiO₂ additives at 1800^oC. Effects of post-sintering heat treatment at different temperature and atmosphere on thermal and mechanical properties of Si₃N₄ ceramics were observed.