In this paper, the criterion on evaluation of EIC (Environment- Induced Cracking) susceptibility for constant load method and a unified EIC mechanism, which are applied to various materials, are newly proposed. The criterion is determined on the basis of the results that the steady state elongation rate becomes the parameter for predicting time to failure and for evaluating the EIC susceptibility. To explain the EIC phenomena obtained experimentally for various materials, the unified EIC mechanism is proposed, by which the roles of three parameters (stress, material and environment) in EIC are more qualitatively explained.
The feasibility of a newly developed biofilm observation technique, COCRM: Continuous-Optimizing Confocal Reflection Microscopy, to an investigation technique for metal/microbial simultaneous observation was examined. According to the COCRM investigation technique, the images of biofilm formation on the test specimen surface and the morphology of metal surface was clearly observed simultaneously. Moreover, continuous 15 h fixed-point in-situ metal/microbial simultaneous observation was performed, then the bacterial movements on the metal surface and the change of the metal surface depending on the time was clearly observed. From the results shown above, the feasibility and the possibility of COCRM to MIC research was confirmed.
The inclusion control is essential for the development of duplex stainless steels with high local corrosion resistance. In this study, the effect of the inclusion control by Ta addition on the crevice corrosion resistance of the super duplex stainless steels was investigated. The Ta-bearing super duplex stainless steels exhibited the higher crevice corrosion resistance compared to the super duplex stainless steels without Ta. In the super duplex stainless steels without Ta, the dissolution of MnS was observed after the crevice corrosion test, indicating that MnS acts as the initiation of the crevice corrosion. In the Ta-bearing super duplex stainless steels, part of MnS was modified to the (Ta, Mn)-oxysulfide which did not dissolve after the same crevice corrosion test as was conducted for the base alloy without Ta. This demonstrates that (Ta, Mn)-oxysulfide is electrochemically-stable. Thus, Ta addition to the super duplex stainless steel improved the crevice corrosion resistance because of a decrease of MnS which was modified to the electrochemically-stable Ta-containing inclusions.
Passive films formed on Alloy 600 and Alloy 690 in the simulated primary water of pressurized water reactor were characterized by photo electrochemical current response focusing on the influence of the dissolved hydrogen and cold working. Some specimens were also analyzed by X-ray photoelectron spectroscopy using the hard X-ray generated by SPring-8. Passive films on both alloys consisted of the oxide layer of p-type semiconductor properties with band gap energy (Eb) of 3.5 eV and the hydroxide layer of n-type semiconductor with Eb of 2.3 eV. However, the content of Ni in the oxide layer which may induce p-type semiconductor property is negligible small. The passive films on Alloy 600 become thinner by dissolved hydrogen, and less protective by cold working. Whereas passive films on Alloy 690, which were more protective than that on Alloy 600, were rarely influenced by cold working and dissolved hydrogen.
The previously developed voltammetric method using a strongly alkaline electrolyte (6 M KOH + 1 M LiOH) as the supporting electrolyte was applied for simultaneous determination of copper corrosion products, including the oxides and patinas. The reduction peaks of these chemical species could be separated in the electrolyte. When the method was applied to samples with patina, the fast exchange reaction presumably occurred between SO42－ or CO32－ ions in patinas and OH－ ions in the electrolyte, so that the reduction peak of patina could be observed at potentials close to that of Cu(OH)2.