The hot corrosion of Fe-Al and Fe-Cr alloys beneath a ZnCl_2-KCl melt at 723 K was comparatively studied in an air atmosphere by exposure test. Different accelerated corrosion behaviours were observed on the alloys examined. A high Cr content in the alloy was not effective to prevent the substrate materials degradation, whereas the corrosion resistance of Fe-Al alloys was significantly improved with increasing Al concentration. Metallic Zn was formed as one of the reaction products on Fe-Al substrates, and its amount on the top surface increases with higher Al concentration in the alloy. Only Zn compounds (oxide or spinel) were detected on those Al-free Fe-Cr substrates. Accordingly, a fluxing mechanism was proposed for the substrate degradation of Fe-Cr alloys, and a displacement reaction mechanism might match with Fe-Al systems.
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