Corrosion behaviour of various model alloys with NaCl-KCl coating

The hot corrosion behaviour of various Fe-Cr, Fe-Al and NiAl model alloys was investigated in air with a surface deposit of NaCl-KCl melt. The results showed that Al is very beneficial by improving the corrosion resistance of Fe-Al alloys with increasing Al content, while Cr exhibits a detrimental effect on corrosion of Fe-Cr alloys. Metallic Ni remains relatively stable and NiAl alloy presents the best corrosion resistance comparing with the other materials. The degradation mechanism of these materials was clarified with respect to the different thermal-chemical stability of metallic Cr, Al and their oxides and chlorides, particularly by considering the high reactivity of Cr and C2O3 with alkali chloride salts. The corrosion trend was basically very similar to the behaviour caused by individual KCl or NaCl.