Effects of Y₂O₃-SiO₂ Additives on the Sintering Properties of the SiC-AlN composites by pressureless sintering

SiC and AlN powders were mixed as raw materials (in mass ratio of 1:1) with Y₂O₃ and SiO₂ (in molar ratio of 2.9:7.1) as sintering additives. SiC-AlN composites were prepared by pressureless sintering in H₂ and Ar atmosphere respectively. The effects of sintering atmosphere, sintering temperature and Y₂O₃-SiO₂ content on the sintering properties were investigated. The results show that the sintered samples in Ar atmosphere are more compact than that in H₂ atmosphere. The compactness improves obviously with the increase of sintering temperature(1650-1850℃). The apparent porosity of the sample was 0.15% at Y₂O₃-SiO₂ additive of 9.09wt% under the condition of argon atmosphere, 1850℃ sintering temperature and 1 hour holding time. SEM analysis of the sintered samples showed that grain size is uniform and grains connected compactly. During the sintering process, under a certain temperature, Y₂O₃, SiO₂ and Al₂O₃ on the surface of the AlN form a liquid phase, which could promote sintering. Y₃Al₅O₁₂ is generated via the reaction of Y₂O₃ and Al₂O₃ on the surface of the AlN. SiO₂ forms glass phase in the sintered samples. The main crystal phase of the sample is 6H-SiC and AlN, and the minor crystal phase is Y₃Al₅O₁₂.