A detailed TEM and SEM study of Ni-base alloys oxide scales formed in primary conditions of pressurized water reactor
A detailed TEM and SEM study of Ni-base alloys oxide scales formed in primary conditions of pressurized water reactor
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DOI：
10.1016/j.jnucmat.2010.05.010
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发表时间：
2010-07
影响因子：
3.1
通讯作者：
M. Sennour;L. Marchetti;F. Martin;S. Perrin;R. Molins;M. Pijolat
中科院分区：
文献类型：
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作者：
M. Sennour;L. Marchetti;F. Martin;S. Perrin;R. Molins;M. Pijolat
在压水堆（PWR）主冷却剂条件下（325°C，含水介质）镍基合金上形成的氧化膜非常薄，厚度在1-100nm之间，这取决于表面状态和腐蚀测试持续时间。用透射电子显微镜（TEM）和扫描电子显微镜（SEM）对其性质和结构进行了研究。透射电镜观察发现氧化层分为两部分。内层主要由连续尖晶石层组成，鉴定为铁镍混合铬铁矿（Ni(1−x)FexCr2O4）。在该尖晶石与合金的界面处存在Cr2O3晶粒，晶粒尺寸约为5nm。在合金/氧化物界面处，没有观察到合金中铬的损耗。外层由析出现象形成的大晶状富铁尖晶石结构(Ni（1−z)Fe(2+z)O4）组成。扫描电镜和透射电镜观察表明，铁素体镍晶的成核和/或生长与基体的晶体取向有关。表面缺陷的存在和晶体成核之间的联系也通过扫描电镜观察得到强调。用透射电镜也观察到了部分水合的氢氧化镍的外部水化。在此基础上，对氧化层形成机理进行了探讨。
The oxide film formed on nickel-based alloys in pressurized water reactors (PWR) primary coolant conditions (325°C, aqueous media) is very thin, in the range of 1–100nm thick, depending on the surface state and on the corrosion test duration. The nature and the structure of this scale have been investigated by Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). TEM observations revealed an oxide layer divided in two parts. The internal layer was mainly composed of a continuous spinel layer, identified as a mixed iron and nickel chromite (Ni(1−x)FexCr2O4). Moreover, nodules of Cr2O3, with a size about 5nm, were present at the interface between this spinel and the alloy. No chromium depletion was observed in the alloy, at the alloy/oxide interface. The external layer is composed of large crystallites corresponding to a spinel structure rich in iron (Ni(1−z)Fe(2+z)O4) resulting from precipitation phenomena. SEM and TEM observations showed a link between the nucleation and/or the growth of crystallites of nickel ferrite and the crystallographic orientation of the substrate. A link between the presence of surface defects and the nucleation of the crystallites was also underlined by SEM observations. Partially hydrated nickel hydroxide, was also observed by TEM in the external scale. Based on these results, some considerations about the mechanism of formation of this oxide layer are discussed.