SZA-4和ZIRLO锆合金在360℃含氧水环境中的腐蚀行为

doi:10.3901/JME.2019.08.088

摘要/Abstract

摘要： 通过动水循环高压釜回路，考察了国产新锆合金SZA-4（Zr-0.85n-0.25Nb-0.35Fe-0.1Cr-0.05Ge）和商用ZIRLO（Zr-1.0Nb-1.0Sn-0.1Fe）合金在含有约2.0 mg/L溶解氧的360℃/20.0 MPa高温高压水中的早期腐蚀行为，用透射电镜分析了两种合金基体和腐蚀30天后氧化膜的显微组织及成分分布。结果表明，SZA-4合金为完全再结晶晶粒和仅发生回复的等轴晶粒组成的“混晶”组织，主要含有富Nb的Zr（Fe，Cr）₂相及少量的Zr₃Fe相，而ZIRLO合金由均匀分布的短板条晶粒组成，主要以β-Nb和Zr（Nb，Fe）2相为主。SZA-4合金在DO环境中的腐蚀增重明显低于商用ZIRLO合金，且随着时间的延长，增重差异逐渐增加。SZA-4合金的氧化膜厚度（1.0～1.2 μm）明显低于ZIRLO合金（1.3～2.0 μm），且含有较少的横向裂纹。SZA-4和ZIRLO合金中的第二相可延迟氧化并“镶嵌”至氧化膜外层等轴晶区，说明未充分氧化或溶解。SZA-4中的Cr能够更好地把Fe“束缚”在Zr（Fe，Cr）₂相中发生原位氧化，而ZIRLO合金中的Fe在Zr（Nb，Fe）₂相初始氧化时即扩散至周围氧化膜中，间接增加了Fe在氧化膜中的浓度。固溶原子Fe和Nb的不同可能是造成两种Zr合金早期腐蚀增重差异的主要原因。

关键词: 腐蚀, 锆合金, 溶解氧, 显微组织, 氧化膜

Abstract: Development of high-performance zirconium alloys with improved corrosion resistant is vital to meet the demands of higher fuel duty, increased cycle length and more aggressive water chemistries, such as potential dissolved oxygen (DO) in some advanced boil water reactor's (ABWR) and small module reactor's (SMR) environment. It is therefore necessary to consider the corrosion behavior of zirconium alloys in DO condition. In the present study, the corrosion behavior of a new-designed SZA-4 alloy (Zr-0.85n-0.25Nb-0.35Fe-0.1Cr-0.05Ge, wt.%) (China) and a reference commercial ZIRLO alloy (Zr-1.0Nb-1.0Sn-0.1Fe) (America) was estimated using an autoclave loop in 360oC/20.0 MPa pure water with approximately 2.0 mg/L DO. TEM was employed to characterize the microstructure of the Zr metal and the oxide film and EDS to give corresponding composition analysis. The results show that, the partial-recrystallized annealing SZA-4 alloy mainly consists of large completely recrystallized grains and small recovered equiaxed grains, with dominant Nb-rich Zr(Fe,Cr)₂ phase and a small amount of Zr₃Fe phase. The stress-relieved annealing ZIRLO alloy is composed of uniformly distributed short-lath grains, with dispersed Nb-containing β-Nb and Zr(Nb,Fe)₂ phase. The weight gain of SZA-4 alloy is obviously lower than that of ZIRLO alloy, and the discrepancy in weight gain increases with prolonged corroded time, which suggests the SZA-4 alloy has better corrosion resistance. After corroded for 30 days, the oxide of both alloys are consists of loose quiaxed grains in outer layer and dense columnar grains in inner layer, which indicates the corrosion is at its pre-transition stage. The oxide of SZA-4 alloy (1.0-1.2μm) was significantly thinner than the ZIRLO alloy (1.3-2.0μm), and contains less transverse cracks. The presence of transverse cracks may be a result of the rapid release of stress in the oxide film during sample preparation. The second phase precipitates (SPPs) in SZA-4 and ZIRLO alloys was not sufficiently oxidized and retained into the oxide film at a certain distance from the oxide/metal boundary. In SZA-4 alloy, Cr tends to "bind" Fe into Zr(Fe,Cr)₂ phase for in-situ oxidation, while in ZIRLO alloy, Fe is readily to diffuse into the surrounding oxide from the Zr(Nb,Fe)₂ phase on its onset of oxidation. The different Fe and Nb content in solid solution is more possibly responsible for the difference in corrosion weight gain for the two Zr alloys at the early stage of corrosion.

Key words: corrosion, dissolved oxygen, microstructure, oxide film, zirconium alloy

中图分类号:

TB37
TL341

刘庆冬, 张浩, 曾奇锋, 卢俊强, 李聪, 张乐福. SZA-4和ZIRLO锆合金在360℃含氧水环境中的腐蚀行为[J]. 机械工程学报, 2019, 55(8): 88-96.

LIU Qingdong, ZHANG Hao, ZENG Qifeng, LU Junqiang, LI Cong, ZHANG Lefu. Pre-transition Corrosion Behavior of SZA-4 and ZIRLO Alloys in Dissolved Oxygen Aqueous Condition at 360℃[J]. Journal of Mechanical Engineering, 2019, 55(8): 88-96.

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