Sosuke Kondo

To assess the strength of coatings under multi‐axial stress conditions, a method was developed to evaluate the biaxial strength of thin silicon carbide (SiC) coatings using a ring‐on‐ring test. A graphite substrate was used as an intermediary to transmit stress from the load ring to the coated specimen, and the thin coating was subjected to a uniform equi‐biaxial stress. The strain in the thin film was continuously monitored using digital image correlation, allowing the identification of the time at which and when the initial crack occurred; the stress applied to the loading area at time was determined to be the fracture strength of the thin SiC films. The obtained fracture strength ranged from 209 to 1014 MPa and was dependent on specimen volume. Notably, the thinnest specimen exhibited the highest strength, whereas the strengths of thicker specimens approached previously reported bulk strengths.

Silicon carbide composites are expected for light water reactors. The objective is to understand the steam oxidation behavior and the high-temperature water corrosion behavior of the liquid phase sintering silicon carbide and to develop the liquid phase sintering silicon carbide composites, which are stable at the high-temperature water conditions in normal operation and the high-temperature steam conditions in a severe accident. The steam oxidation experiments were carried out at 1200 and 1400 °C. The high-temperature water corrosion experiments were carried out at 320 and 360 °C. The formation of the silicate, which is expected to have excellent resistance to the steam, was confirmed following the steam exposure at 1400 °C. High-temperature water corrosion resistance was improved by the formation of Yttrium Aluminum Garnet at the grain boundary. The particle-dispersion silicon carbide composite tubes with the modified condition were developed, and the thermal shock experiments from 1200 °C to ambient temperature were carried out. The composite tubes showed excellent oxidation and thermal shock resistance. The particle-dispersion liquid phase sintering silicon carbide composites with the modified condition are promising materials for light water reactors.