电解抛光工艺对600合金在高温高压水环境中腐蚀行为的影响

Effects of Electropolishing Processes on Corrosion Behaivor of Alloy 600 in High Temperature and High Pressure Water Environment

从电解抛光影响合金表面化学成分与结构的角度出发,利用扫描电镜(SEM)、X射线光电子能谱(XPS)等方法研究了硝酸-甲醇(0℃,10s,3V)和硫酸-磷酸-水(70℃,30s,0.2A/cm2)两种不同电解抛光液对600合金在高温高压水环境中腐蚀行为的影响。结果表明:经硝酸-甲醇溶液抛光后(EPS-1),试样表面的初始产物膜比经硫酸-磷酸-水(EPS-2)溶液抛光后的厚,且EPS-1产物膜中氢氧化物的含量比EPS-2中的高;高温高压水环境腐蚀试验后两种抛光表面都形成双层结构氧化膜,即富铬内层和分散的富镍、铁氧化物颗粒外层;EPS-2产物膜中氢氧化物含量低于EPS-1的且铬含量高于EPS-1的,EPS-2产物膜的致密性和保护性更好,能有效减缓腐蚀进程,形成较薄的氧化膜。分析认为这是由于在两种溶液中电解抛光后样品表面形成了成分与结构不同的初始产物膜。

Effects of the changes in surface composition and microstructure caused by two different electropolishing processes on corrosion of alloy 600 in high temperature and high pressure water were investigated. The first electropolishing process was conducted in a HNO3-CH3OH electrolyte at 0 ℃ for 10 s at 3 V. The second was conducted in a H2SO4-H3PO4-H2O electrolyte at 70 ℃ for 30 s at 0. 2 A/cm2. X-ray photoelectron spectroscopy （XPS） analysis of the primary surfaces after the two electropolishing processes revealed that the surface electropolished by the first process （EPS-1） had a thicker primary film than that electropolished by the second process （EPS-2）. A higher content of hydroxides in EPS-1 was also observed. After the corrosion test in high temperature and high pressure water, duplex-structure oxide scale was observed on both surfaces. XPS analysis of the oxide scale showed that the scale formed in EPS-2 at the early stage of corrosion had a lower content of hydroxides and a higher content of Cr than that in EPS-1. This suggests the scale in EPS-2 has a better protectability, which is most likely the cause for the formation of a thinner oxide scale in EPS-2 in the subsequent exposures. The difference in the corrosion behavior of EPS-1 and EPS-2 was attributed to the difference in composition and structure of the primary films formed on alloy 600 by the two electropolishing processes.