| Aqueous corrosion characteristics of iron aluminides in thiosulfate-chloride solution were studied as a function of chromium content. Four kinds of iron aluminides, FA-61, FA-77, FA-72 and FA-78, were prepared by arc melting followed by the thermomechanical treatment. The corrosion behavior in thiosulfate-chloride solution for the prepared alloys was investigated by electrochemical tests(potentiodynamic test, potentiostatic test and electrochemical impedance spectroscopy(EIS) measurement) and surface analyses(SEM, AES). The results of potentiodynamic test indicated that the breakdown potential increased with increasing Cr content. Cr additions were found to prevent passive film from undergoing pitting corrosion. EIS measurements showed that semicircle was less depressed when the Cr content increased. Furthermore, the Cr-bearing alloys present higher pitting resistance than a Mo-free alloy at breakdown state. The SEM observations of the metal surfaces revealed that the Cr additions changed pit morphology from hemispherical to tunneling attack. The AES results gave the evidence that the thiosulfate was reduced on the metallic surface, which inhibited the repassivation process. |
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