Microstructure of silicon carbide with yttrium-aluminum garnet and silica

Abstract

By using Y3Al5O12 (YAG) and SiO2 as sintering additives, the effect of the additive compositions on microstructures and mechanical properties of the hot-pressed and subsequently annealed SiC materials were investigated. Microstructures of annealed materials were strongly dependent on the compositions of the sintering additives. The average diameter and volume fraction of elongated grains in the materials increased with increasing the SiO2/YAG ratio. In contrast, the density of the materials decreased with increasing the SiO2/YAG ratio because of the increased weight loss. Extremely low SiO2 content in the starting composition resulted in equiaxed microstructure, even though the beta-->alpha phase transformation occurred during annealing. With increasing the SiO2/YAG ratio, the strength of the materials decreased while the fracture toughness increased.