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 β-NiAl and developmental Pt + Hf-modified γ′-Ni3Al + γ-Ni coatings under Type II (705 °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 γ′ + γ coating exhibited superior Type II hot corrosion resistance with the pre-oxidation treatment; while, the Pt-modified β coating exhibited the best Type II hot corrosion resistance when no pre-oxidation treatment was given. Interestingly, pre-oxidation of the Pt-modified β 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 β coatings; whereas, the presence of Hf and a relatively high Al content in the γ′ + γ coatings is beneficial. Moreover, the results from this study clearly revealed the need to pre-oxidize the γ′ + γ coatings at elevated temperatures (i.e., greater than ∼ 1050 °C) in order to achieve excellent hot corrosion resistance.