Evaluation of the hot corrosion resistance of commercial β-NiAl and developmental γ′-Ni3Al + γ-Ni-based coatings

This study evaluates the performance of commercially available beta-NiAl and developmental Pt + Hf-modified gamma'-Ni3Al + gamma-Ni coatings under Type II (705 degrees C) hot corrosion conditions. A further variable studied was the effect(s) of pre-oxidation treatment on subsequent hot corrosion resistance. The hot corrosion performances (with and without pre-oxidation treatment) were assessed by analyzing weight-change behavior and cross-sectional images of the corroded samples. It was found that the gamma' + gamma coating exhibited superior Type II hot corrosion resistance with the pre-oxidation treatment; while, the Pt-modified beta coating exhibited the best Type II hot corrosion resistance when no pre-oxidation treatment was given. Interestingly, pre-oxidation of the Pt-modified beta coating was not beneficial to Type II hot corrosion resistance, due, it is believed, to Al depletion from the coating during the pre-oxidation treatment. It was also found that Pt addition is beneficial in improving the hot corrosion resistance of beta coatings; whereas, the presence of Hf and a relatively high Al content in the gamma' + gamma coatings is beneficial. Moreover, the results from this study clearly revealed the need to pre-oxidize the gamma' + gamma coatings at elevated temperatures (i.e., greater than similar to 1050 degrees C) in order to achieve excellent hot corrosion resistance. (c) 2007 Elsevier B.V. All rights reserved.