Effect of Al contained in polymer‐derived SiC crystals on creating stable crystal grain boundaries

Abstract Si‐Al‐C‐O materials are well‐known as a good precursor material for obtaining a dense, excellent heat‐resistant SiC polycrystalline materials. Although it has been found that the aluminum contained in Si‐Al‐C‐O materials plays an important role in obtaining dense SiC materials, its actual behavior during heat‐treatment processes has not been investigated. In this study, we investigated the behavior of aluminum contained in the SiC crystals, during the densification of SiC crystals produced from the Si‐Al‐C‐O material. A part of the aluminum contained in the SiC crystals plays an important role in creating a thermodynamically stable grain boundary by the diffusional transportation of aluminum to the SiC grain boundaries at temperatures above 1700°C. Subsequently, most of the aluminum disappeared during the heat treatment at higher temperatures (~1900°C); as a consequence, a dense SiC solid solution with uniformly distributed residual aluminum (0.15wt%) was formed without a secondary phase at the grain boundary.