Effect of composition on the oxidation and hot corrosion resistance of NiAl doped with precious metals

Cast NiAl alloyed with Cr, Pt, Pd, Ir and Ru was tested in l-h cycles at 950 degreesC under hot corrosion conditions and at 1150 degreesC in oxygen. For comparison, Hf-doped NiAl variants and a cast NiPtAl alloy resembling the composition of commercial aluminide coatings were included. Cr was the only element that reduced hot corrosion attack of NiAl significantly. However, at higher temperatures, addition of Cr to Hf-doped NiAl accelerated the alumina scale growth rate and promoted spallation of the oxide scale. The results from initial detailed characterization indicate that rejection of chromium at the metal-oxide interface gives rise to the formation of chromium-rich precipitates in the alloy, which apparently modify its oxidation behavior. This suggests that for NiAl-based substrates, hot corrosion resistance and exceptional scale spallation resistance may be mutually incompatible goals. (C) 2000 Elsevier Science B.V. All rights reserved.