High-Temperature Fracture Strength of a CVD-SiC Coating Layer for TRISO Nuclear Fuel Particles by a Micro-Tensile Test

Abstract

Silicon carbide (SiC) coatings for tri-isotropic (TRISO) nuclear fuel particles were fabricated using a chemical vapor deposition (CVD) process onto graphite. A micro-tensile-testing system was developed for the mechanical characterization of SiC coatings at high temperatures. The fracture strength of the SiC coatings was characterized by the developed micro-tensile test in the range of 25°C to 1000°C. Two types of CVD-SiC films were prepared for the micro-tensile test. SiC-A exhibited a large grain size (0.4~0.6 m) and the [111] preferred orientation, while SiC-B had a small grain size (0.2~0.3 mm) and the [220] preferred orientation. Free silicon (Si) was co-deposited onto SiC-B, and stacking faults also existed in the SiC-B structure. The fracture strengths of the CVD-SiC coatings, as measured by the high-temperature micro-tensile test, decreased with the testing temperature. The high-temperature fracture strengths of CVD-SiC coatings were related to the microstructure and defects of the CVD-SiC coatings.