EFFECTS OF PRE-OXIDATION ON HOT CORROSION RESISTANCE OF Al–Si COATINGS

Abstract

In this study, effects of pre-oxidation on the hot corrosion behaviour of Al–Si coatings in a Na2SO4 and 25 w/% NaCl mixture at 900 °C were investigated. The results showed that after 120 h of corrosion, a large amount of β-NiAl residual was found with no obvious sulphides or oxidation in the pre-oxidised Al–Si coating. The pre-formed oxide film on the pre-oxidised coating prevented external O2– and species such as S2– and Cl– from the molten salts from directly contacting the coating and reduced the rate of TiO2 formation in the oxide layer, thus forming an Al2O3-based oxide film and reducing the growth rate of the oxide film on the coating surface. Cracking and peeling of the oxide film, caused by the internal stress owing to the difference in the thermal expansion coefficient between the oxides in the oxide layer, are suppressed; thus, the hot corrosion resistance of the coating is significantly improved.
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