Resistance of slurry aluminide coatings on pure nickel under different sulphidizing/Hot corrosion conditions at 700 °C.

A water-based slurry aluminide coating was elaborated on high-purity nickel and tested in synthetic air, synthetic air + 0.5 % SO 2 /SO 3 and synthetic air + 0.5 % SO 2 /SO 3 with sodium sulphate (Na 2 SO 4) deposit at 700 °C. The developed coating considerably increased the oxidation-sulphidation resistance of nickel in the absence of salt through the formation of thin and adherent alumina scales. In contrast, the presence of sodium sulphate decreased the corrosion resistance. Microstructural investigations indicated that aluminium depletion and the related formation of Ni-rich oxides is mainly responsible for the onset of the corrosion attack following sulphation reaction and fluxing mechanisms. [Display omitted] • Coating based on β-NiAl increases sulphidation resistance through protective α-Al 2 O 3. • Coating offers limited protection after the incubation period when in contact with solid Na 2 SO 4. • Initiation of the attack due to fluxing and synergistic dissolution of NiO and Al 2 O 3. • Aluminium surface concentration and phase transformation are key factors on the onset of the hot corrosion attack. • Microstructural observations confirm the formation of the eutectic Na 2 SO 4 -NiSO 4 in Type II conditions. [ABSTRACT FROM AUTHOR]