2002 Volume 43 Issue 10 Pages 2622-2628
The microstructures of slurry Si-modified aluminide coatings on Ni-base superalloy In-738LC have been investigated using SEM, TEM, EDS and XRD . The corrosion performance of the coatings has been also investigated by hot corrosion and cyclic oxidation tests. In order to evaluate the hot corrosion performance, the anodic polarization curves were measured in Na2SO4–25 mol%NaVO3–5 mol%NaCl at 1053 K . The cyclic oxidation test was carried out by exposure to alternate conditions of air atmosphere at 1373 K and room temperature. The analyses of SEM, EDS and XRD were also used to characterize attack morphologies of the coatings exposed to the test conditions. The results showed that the heat-treated slurry Si-modified aluminide coating was composed of β-NiAl phase including fine precipitates, which were found to be complex silicides. The results of hot corrosion tests indicated that at least 10–13 mass%Si in the coating layer is needed to improve the corrosion resistance of the aluminide coating. The coatings that met this criterion also showed a good cyclic oxidation resistance.
