Electrochemical study on hot corrosion of Si-modified aluminide coated In-738LC in Na2SO4–20 wt.% NaCl melt at 750 °C
Electrochemical study on hot corrosion of Si-modified aluminide coated In-738LC in Na2SO4–20 wt.% NaCl melt at 750 °C
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DOI：
10.1016/s0010-938x(02)00127-0
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发表时间：
2003-05
影响因子：
8.3
通讯作者：
K. Shirvani;M. Saremi;A. Nishikata;T. Tsuru
中科院分区：
文献类型：
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作者：
K. Shirvani;M. Saremi;A. Nishikata;T. Tsuru
研究了镍基高温合金In-738 LC表面硅改性铝化物涂层在Na_2SO_4 -20 wt.%溶液中的低温热腐蚀性能通过结合使用阳极极化和表征技术，在750 °C下对NaCl熔体进行测试。涂层试样在高达-0.460 V（相对于Ag/AgCl（0.1摩尔分数）参比电极）时表现出钝化行为，随后由于在较高电位区域的局部攻击，阳极电流迅速增加。在钝化区，涂层成分通过钝化膜（可能是SiO2）以20-30 μA/cm ~ 2的缓慢速率发生阳极溶解。Si改性涂层的钝化电流比裸In-738 LC小两个数量级，裸In-738 LC在该熔体中被称为Cr2 O3形成剂。这表明在此条件下SiO2膜比Cr2 O3膜更稳定。在+0.400 V以上的电位区，点蚀以100 mA/cm 2的速率发生。采用SEM、EDS和XRD对不同阳极电位极化后涂层上的腐蚀产物进行了表征。从表征中发现，氧化是主要的侵蚀模式，并且在750 °C下没有发生显著的硫化。由于钝化膜的厚度非常薄，因此在钝化区中没有SiO2氧化物的特征，但是在局部腐蚀区中检测到作为主要氧化物的SiO2氧化物，其中通过腐蚀攻击前沿进一步进展到涂层的内层中观察到Al的选择性氧化。
The corrosion performance of the slurry Si-modified aluminide coating on the nickel base superalloy In-738LC exposed to low temperature hot corrosion condition has been investigated in Na2SO4–20 wt.% NaCl melt at 750 °C by combined use of the anodic polarization and characterization techniques. The coated specimen showed a passive behavior up to −0.460 V vs. Ag/AgCl (0.1 mol fraction) reference electrode, followed by a rapid increase in anodic current due to localized attack in the higher potential region. In the passive region, the anodic dissolution of constituents of the coating occurred through the passive film, probably SiO2, at slow rate of 20–30 μA/cm2. The passive current for the Si-modified coating was two orders of magnitude smaller than that for bare In-738LC, which is known as Cr2O3former in this melt. This indicates that the SiO2film is chemically more stable than Cr2O3film under this condition. However, pitting-like corrosion commenced around −0.460 V and proceeded at the high rate of 100 mA/cm2in the higher potential region than +0.400 V. The corrosion products formed on the coating polarized in different anodic potentials were characterized by SEM, EDS and XRD. It was found from the characterization that oxidation was dominant attack mode and no considerable sulfidation occurred at 750 °C. The SiO2oxide was not characterized in the passive region because the thickness of the passive film was extremely thin, but was detected as the primary oxide in the localized corrosion region, where the selective oxidation of Al was observed by further progress of the corrosion attack front into the inner layer of coating.