ANALYSIS OF SURFACE OXIDE FILM FORMED ON ELETROPOLISHED ALLOY 690TT IN HIGH TEMPERATURE AND HIGH PRESSURE WATER WITH SEQUENTIALLY DISSOLVED HYDROGEN AND OXYGEN
ZHANG Zhiming1,2, WANG Jianqiu1,2(), HAN En-Hou1,2, KE Wei1,2
1 Key Laboratory of Nuclear Materials and Safety Assessment, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 2 Liaoning Key Laboratory for Safety and Assessment Technique of Nuclear Materials, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016
Cite this article:
ZHANG Zhiming, WANG Jianqiu, HAN En-Hou, KE Wei. ANALYSIS OF SURFACE OXIDE FILM FORMED ON ELETROPOLISHED ALLOY 690TT IN HIGH TEMPERATURE AND HIGH PRESSURE WATER WITH SEQUENTIALLY DISSOLVED HYDROGEN AND OXYGEN. Acta Metall Sin, 2015, 51(1): 85-92.
The electropolished (EP) alloy 690TT samples were first oxidized in the simulated B and Li containing primary water with 2.5 mg/L H2 at 325 ℃ and 15.6 MPa for 720 h, and then half of the samples were continuously immersed in this solution with 2.0 mg/L O2 for another 720 h. The microstructures and chemical composition of the oxide films formed under the above two conditions were analyzed. The results show that the dual layered oxide film formed under the single hydrogen water chemistry is mainly composed of spinel oxides. The outer layer is composed of big oxide particles rich in Ni and Fe and the underlying loose needle-like oxides rich in Ni. The inner layer is continuous Cr-rich oxides. The oxide film formed on EP alloy 690TT under the hydrogen/oxygen water chemistry also shows a dual layered structure. The surface morphology and chemical composition of the outer layer are similar to the oxide film formed under the hydrogen water chemistry. However, the inner layer is changed to the nano-sized NiO. The stable phase region in the potential-pH diagram for the Ni oxides is enlarged by the later dissolved oxygen. As a result, the oxygen promotes the fast growth of the outer needle-like oxides rich in Ni. Further, the oxygen promotes the dissolution of the inner Cr-rich oxides formed under the hydrogen water chemistry and increases the corrosion rate of the EP alloy 690TT. Electropolishing treatment can not reduce the corrosion rate of alloy 690TT in the simulated primary water with sequentially dissolved hydrogen and oxygen.
Fund: Supported by National Basic Research Program of China (No.2011CB610502), National Science and Technology Major Project (No.2011ZX06004-009) and National Natural Science Foundation of China (No.51025104)
Fig.1 SEM images of surfaces of oxide films grown on electropolished (EP) alloy 690TT after immersion in hydrogenated primary water for 720 h (DH) (a) and in hydrogenated primary water for 720 h, in oxygenated primary water for 720 h (DH/DO) (b)
Fig.2 GIXRD patterns of oxide films grown on EP alloy 690TT after immersion in hydrogenated primary water for 720 h (a) and in hydrogenated primary water for 720 h, in oxygenated primary water for 720 h (b)
Immersion condition
Ni
Cr
Fe
DH
38.74
7.93
53.33
DH/DO
45.01
7.21
47.77
Fig.3 Cross-sectional TEM image of surface oxide film grown on EP alloy 690TT after immersion in hydrogenated primary water for 720 h (a) and local enlargement of the area shown in Fig.3a by the rectangle (b)
Position
Ni
Fe
Cr
1
24.24
72.87
2.89
2
62.63
21.50
15.87
3
13.82
12.38
73.80
4
59.44
11.05
29.50
Fig.4 Cross-sectional TEM image of surface oxide film grown on EP alloy 690TT after immersion in hydrogenated primary water for 720 h, in oxygenated primary water for 720 h (a), local enlargement of the area shown in Fig.4a by the rectangle (b), image of inner layer taken at high magnification (c) and HRTEM of inner layer (d) (OP—oxide particle, AO—amorphous oxide)
Fig.5 SAED patterns of different crystals shown by positions 1 (a), 2 (b) and 3 (c) in Fig.4, respectively
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