Microstructure and mechanical properties evolution of thermal-treated SiC layer with fine grain size in TRISO particles

Abstract

The previous studies showed that the SiC layer in TRISO particle with smaller grain sizes can provide better mechanical property, higher oxidation resistance, and containment of fission products more effectively. Hence, the behavior of fine-grained SiC layer at high temperatures is of great significance. However, there are little reports on the effect of high temperature properties of SiC layers with fine-grained size. This study investigated the phase change, evaporation process, microstructure and hardness and Young’s modulus change of SiC layers with fine-grained size after high temperatures. The experiment result indicated that the amorphous SiC have a better crystallinity after high-temperature treatment. Especially, it could be observed that there is an evaporation-precipitation process of SiC layer at 1800 °C. So the intact OPyC layer can act as an effective obstacle to this process. When the fine-grained SiC was annealed at 1900°C, the grain size of the fine SiC layer increased to about 600 nm from 100 nm. Moreover, a novel formation mechanism of the pores in SiC layers is proposed. The results showed that the fine-grained SiC layers have better resistance to the formation of the pores at high temperatures than the SiC layers with large size. Besides, the fine-grained SiC layers show higher hardness and Young’s modulus than larger SiC layers before and after 1900°Cannealing. This research will further our understanding of the high temperature resistance of the fine-grained SiC layers and its crucial role in TRISO particles.