High thermal conductivity silicon nitride ceramics prepared by pressureless sintering with ternary sintering additives

Abstract Silicon nitride ceramics were pressureless sintered at low temperature using ternary sintering additives (TiO 2 , MgO and Y 2 O 3 ), and the effects of sintering aids on thermal conductivity and mechanical properties were studied. TiO 2 –Y 2 O 3 –MgO sintering additives will react with the surface silica present on the silicon nitride particles to form a low melting temperature liquid phase which allows liquid phase sintering to occur and densification of the Si 3 N 4 . The highest flexural strength was 791(±20) MPa with 12 wt% additives sintered at 1780°C for 2 hours, comparable to the samples prepared by gas pressure sintering. Fracture toughness of all the specimens was higher than 7.2 MPa·m 1/2 as the sintering temperature was increased to 1810°C. Thermal conductivity was improved by prolonging the dwelling time and adopting the annealing process. The highest thermal conductivity of 74 W/(m∙K) was achieved with 9 wt% sintering additives sintered at 1810°C with 4 hours holding followed by postannealing.