Influence of Dissolved Hydrogen Concentration on the Protective Property of Oxide Film of Alloy 600 against Primary Water Stress Corrosion Cracking

IF 1.3 4区材料科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY Corrosion Pub Date : 2022-07-19 DOI:10.5006/4109

Kenta Kakitani, Takaaki Kobayashi, Kenji Sato, Wataru Sugino, Yusuke Nakano, T. Shoji, Hiroaki Abe

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引用次数: 2

Abstract

Primary water stress corrosion cracking (PWSCC) of alloy 600 has been a key issue in the field of nuclear energy. It is well known that dissolved hydrogen (DH) plays a crucial role in PWSCC initiation, and some studies showed that PWSCC initiation could be mitigated by decreasing the DH concentration. However, there is no consensus on the mechanism of the PWSCC mitigation in a low DH environment. Hence, to reveal the protective property of the passive film formed in various levels of DH, we analyzed the oxide film formed in simulated primary water at 345°C with the DH concentrations of 5 and 30 cc/kg-H2O by electrochemical measurements (electrochemical impedance spectroscopy and Mott–Schottky test) and transmission electron microscopy (energy-dispersive X-ray spectroscopy and electron energy loss spectroscopy) where the specimens of interest were tested by reverse U bend (RUB) tests, and it was confirmed that the PWSCC initiation time was longer for 5 cc/kg-H2O DH than for 30 cc/kg-H2O DH. Electrochemical measurements showed that the oxide film for the lower DH environment (5 cc/kg-H2O) had a higher electrical resistance and lower defect density than those for the higher DH (30 cc/kg- H2O). The microscopic observation indicated that the intergranular oxidation was relatively insignificant in the lower DH environment. The oxide film for both DH conditions consisted of outer oxides and inner Cr-rich barrier layer. The inner layer for 5 cc/kg-H2O DH had a higher concentration of Fe and a greater ratio of Fe3+/Fe2+ than that for 30 cc/kg-H2O DH. The results suggested that Fe3+ contributed to the formation of a less defective spinel-type structure in the inner oxide in the lower DH environment and thereby provided the alloy surface with corrosion protection. This protective oxide film prevented the intergranular oxidation and led to the mitigation of PWSCC initiation in a low DH environment.

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溶解氢浓度对600合金氧化膜一次水应力腐蚀开裂防护性能的影响

600合金的一次水应力腐蚀开裂（PWSCC）一直是核能领域的一个关键问题。众所周知，溶解氢（DH）在PWSCC引发中起着至关重要的作用，一些研究表明，降低DH浓度可以减轻PWSCC的引发。然而，对于在低DH环境中减轻PWSCC的机制，并没有达成共识。因此为了揭示在不同水平DH中形成的钝化膜的保护特性，我们通过电化学测量（电化学阻抗谱和莫特-肖特基测试）和透射电子显微镜（能量色散X射线谱和电子能量损失谱）分析了在345°C、DH浓度为5和30 cc/kg-H2O的模拟一次水中形成的氧化膜，其中感兴趣的样品通过反向U形弯曲（RUB）进行了测试测试，并且证实了5 cc/kg-H2O DH的PWSCC起始时间长于30 cc/kg-H2 O DH。电化学测量表明，与较高DH（30cc/kg-H2O）相比，较低DH环境（5cc/kg-H2O）下的氧化膜具有更高的电阻和更低的缺陷密度。微观观察表明，在DH较低的环境中，晶间氧化相对不显著。两种DH条件下的氧化物膜由外部氧化物和内部富Cr阻挡层组成。5cc/kg-H2O DH的内层具有比30cc/kg-H2 O DH更高的Fe浓度和更大的Fe3+/Fe2+比率。结果表明，在较低的DH环境中，Fe3+有助于在内部氧化物中形成缺陷较小的尖晶石型结构，从而为合金表面提供防腐保护。这种保护性氧化膜防止了晶间氧化，并导致在低DH环境中PWSCC引发的缓解。

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来源期刊

Corrosion MATERIALS SCIENCE, MULTIDISCIPLINARY-METALLURGY & METALLURGICAL ENGINEERING

CiteScore

2.80

自引率

12.50%

发文量

审稿时长

3 months

期刊介绍： CORROSION is the premier research journal featuring peer-reviewed technical articles from the world’s top researchers and provides a permanent record of progress in the science and technology of corrosion prevention and control. The scope of the journal includes the latest developments in areas of corrosion metallurgy, mechanisms, predictors, cracking (sulfide stress, stress corrosion, hydrogen-induced), passivation, and CO2 corrosion. 70+ years and over 7,100 peer-reviewed articles with advances in corrosion science and engineering have been published in CORROSION. The journal publishes seven article types – original articles, invited critical reviews, technical notes, corrosion communications fast-tracked for rapid publication, special research topic issues, research letters of yearly annual conference student poster sessions, and scientific investigations of field corrosion processes. CORROSION, the Journal of Science and Engineering, serves as an important communication platform for academics, researchers, technical libraries, and universities. Articles considered for CORROSION should have significant permanent value and should accomplish at least one of the following objectives: • Contribute awareness of corrosion phenomena, • Advance understanding of fundamental process, and/or • Further the knowledge of techniques and practices used to reduce corrosion.