Effect of coating temperature on properties of the SiC layer in TRISO-coated particles

The effect of coating temperature on properties of the SiC layer in TRISO-coated particles was investigated. An increase in coating temperature resulted in a significant coarsening of surface microstructures and an increase of the pore size and porosity of SiC layers. The SiC layers formed at 1400–1550 °C had nearly stoichiometric compositions whereas the SiC layer formed at 1600 °C contained a small amount of free carbon. The degradation of hardness and elastic modulus of the SiC layers coated at 1550 and 1600 °C was attributed to the increased porosity of the specimens and partly to the existence of free carbon. The fracture stress of the SiC layer measured by the crush test of hemispherical shell specimen did not correlate with the hardness and elastic modulus, and there was no clear dependence of the fracture stress on the coating temperature; this lack of correlation can be explained by the large roughness of the inner surface of the SiC layer.