A study of the microstructure and vickers indentation fracture toughness of silicon carbide coatings on triso fuel particles

In this study, the microstructure and Vickers indentation fracture toughness (VIF fracture toughness) of three different types of silicon carbide (SiC) coatings (stoichiometric SiC, SiC with excess silicon and SiC with excess carbon) were investigated. SiC coatings were produced on tri-isotropic fuel particles by fluidized bed chemical vapor deposition (FBCVD). The microstructure was investigated using a scanning electron microscope (SEM) and X-ray diffraction, while a transmission electron microscope was used for the analysis of defects and micro-cracks. The VIF fracture toughness was measured using Vickers indentation. The fracture beneath the indenter consists of Palmqvist cracks as observed using SEM. Based on this crack mode, VIF fracture toughness values of 3.51, 4.03, and 4.93 MPa·m ^1/2 for stoichiometric, extra-C and extra-Si SiC coatings were obtained, respectively. It was found that stress-induced micro-cracks seem to be a mechanism for the fracture behavior, which gave SiC coatings with high VIF fracture toughness. The difference in the VIF fracture toughness of FBCVD SiC coatings is discussed in terms of defects and grain morphology.