Compositional Factors Affecting Protective Alumina Formation Under Type II Hot Corrosion Conditions
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The Type II (700 °C) hot corrosion resistance of Ni–36Al (at.%) base alloys with various additions of Pt, Co, and/or Cr was investigated. It was found that the addition of either 5 at.% Pt or 5 at.% Cr was highly beneficial, i.e., extended the protective incubation stage. This was shown, via a thorough examination of the scales formed on these alloys during 700 °C oxidation, to be due to an enhanced ability to rapidly form a protective, pure Al2O3 scale. Addition of either 5 at.% Cr or 5 at.% Co to a Ni–36Al–5Pt alloy was found to be highly detrimental. These latter results are explained by examining subsurface phase transformations that occur during exposure; extensive transient oxidation was also found to play a significant role in the presence of Co.
KeywordsType II hot corrosion Alumina Nickel aluminide Incubation stage
This work was funded by the U. S. Office of Naval Research under project number N00014-10-1-0661. We gratefully acknowledge Dr. David Shifler, the program manager for this project. Also, thanks are due to Prof. Arthur Heuer and Dr. David Hovis at Case Western Reserve University for the XPS and TOF–SIMS analyses.
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