利用AFM, SEM, TEM, EDS及XPS分析了电解抛光处理690TT合金在含B和Li, 充 H2的高温高压水溶液中经不同时间浸泡后表面生长氧化膜的微观结构. 结果表明, 从短期氧化到长期氧化, 氧化膜表面形貌变化不明显; 氧化膜主要由具有尖晶石结构的氧化物和单质Ni构成. 浸泡720, 1440和2160 h后, 氧化膜均由外层、中间层和内层构成: 外层是分散的富含Ni和Fe的尖晶石结构的大颗粒氧化物; 中间层是疏松的富含Ni的尖晶石结构的针状氧化物; 内层是连续致密的富Cr氧化物. 仅氧化膜中的内层氧化物能对基体起到良好的保护作用. 电解抛光处理不利于690TT合金表面保护性氧化膜的快速生长. 浸泡至2160 h后, 氧化膜依然缺乏保护性, 内层氧化膜的平均生长速率并未显著降低.
The corrosion of Ni base alloys in high temperature and high pressure water is affected by samples surface statuses. The morphologies and structures of surface oxide films grown on electropolished (EP) alloy 690TT after immersion in the simulated hydrogenated primary water of pressured water reactors (PWRs) for different times were analyzed by AFM, SEM, TEM, EDS and XPS. After immersion for 15 and 35 h, the EP alloy 690TT samples were covered with columnar oxides. With the increase of the immersion time, the sample surfaces were covered with scattered big oxide particles and loose needle-like oxides. Regardless of the immersion time, the formed oxide films are composed of spinel oxides and metallic Ni. After immersion for 720, 1440 and 2160 h, the oxide films are composed of three layers: the outmost layer is the separated big oxide particles which are rich in Fe and Ni; the intermediate layer is the loose needle--like oxides rich in Ni; the inner layer is the continuous and compact Cr oxides. The peak decomposition of the XPS revealed that the Cr oxides in the inner layer are probably Cr2O3. Only the inner layer in the oxide film could restrain the outward diffusion of metal atoms and also the inward diffusion of the oxygen atoms and then played the role of barrier layer well. Electropolishing treatment disadvantaged the fast growth of protective oxide film on alloy 690TT in the studied solution. The average corrosion rate of the inner layer does not decrease gradually with increasing the immersion time. After immersion for 2160 h, the oxide film still could not protect the matrix from further corrosion.
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