Evaluation of Hot Corrosion Resistance of Alloys and Al Diffusion Coatings under Molten Sulfate film by Electrochemical Techniques

摘要

EIS (Electrochemical Impedance Spectroscopy) is known as a useful tool for monitoring corrosion degradation process of materials at room temperature. Although many researches have been conducted on hot corrosion behavior of alloys by using electrochemical techniques, most of them were carried out in bulk molten salt. In this study, EIS was applied to the evaluation of hot corrosion resistance of alloys and corrosion protective coatings under molten sulfate film condition which is considered to be closer to the real industrial environment than tests conducted in bulk molten salt. A special electrochemical cell system was designed for this impedance monitoring under molten salt film condition. From the results of this research, alloys showed different behavior with the change of partial pressure of oxygen, meaning that atmosphere has much greater affect on corrosion behavior of alloys under molten salt film condition than that in bulk molten salt. On the other hand, no obvious change in corrosion resistance has been found by changing atmosphere for Al diffusion coatings. It was found that by monitoring impedance change at high frequency, more information about change of molten salt resistance or oxide film resistance can be obtained. The results obtained from EIS monitoring were well correlated with the results of SEM observation and EPMA element analysis. Electrochemical techniques are very useful for evaluation of hot corrosion resistance of materials under molten salt film condition.