Abstract
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 1800oC. Effects of post-sintering heat treatment at different temperature and atmosphere on thermal and mechanical properties of Si3N4 ceramics were observed.
