[en] Austenitic stainless steels used for PWR core internal components degrade in the environment of radiation and high temperature water during their long-term service. As they suffer from intergranular cracking at the neutron fluence over the critical value, this degradation mechanism termed irradiation assisted stress corrosion cracking (IASCC) is one of the hot issues in light water reactor (LWR) industry to aim at pursuing license renewal of commercial reactors. Much attention has been paid to an understanding of the IASCC mechanism, which is yet to be achieved. IASCC appears to be very similar to intergranular stress corrosion cracking (IGSCC) in view of intergranular cracking but the former differs from the latter because the former can occur even without corrosion. Consequently, intergranular cracking of IASCC should be taken into account from mechanistic view points. The aim of this study is to analyze the IASCC susceptibility of austenitic stainless steels in view of material compositions and the environment, and hence to guide research directions to take in order to elucidate the IASCC mechanism

[en] We have studied the hot-pressing behavior of ZrB₂/SiC ultra-high temperature ceramics (UHTCs) as a function of: (i) SiC starting-powder size, (ii) SiC vol%, (iii) ZrO₂ doping, and (iv) colloidal dispersion of ZrB₂/SiC powder mixtures. It has been found that the addition of SiC promotes densification of ZrB₂ at a moderate hot-pressing temperature of 1650 deg. C. It has also been found that ball-milling of the ZrB₂/SiC starting-powder mixtures using ZrO₂ balls media results in the doping of the powder mixture with ZrO₂, which promotes hot-pressing densification. Reduction in the SiC starting-powder size, and colloidal dispersion of the powders, both have been found to promote hot-pressing densification of ZrB₂/SiC materials; the highest density achieved in such ZrB₂/SiC ceramics is 99.9%. Detailed microstructural characterization of the ZrB₂/SiC ceramics using electron microscopy shows that some of these materials contain a Zr(O,B)₂ phase, and amorphous films at interphase interfaces. Oxidation studies reveal that SiC grain-size reduction results in improved oxidation-resistance in ZrB₂/SiC materials. The ZrB₂/SiC ceramics produced here possess modest hardness and toughness properties. The results presented here point to a new strategy for improving processing and oxidation-resistance of ZrB₂/SiC materials: dispersion and reduction of SiC grains