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 95 0 degreesC under hot corrosion conditions and at 1150 degreesC in oxygen. F or comparison, Hf-doped NiAl variants and a cast NiPtAl alloy resembling th e composition of commercial aluminide coatings were included. Cr was the on ly element that reduced hot corrosion attack of NiAl significantly. However , at higher temperatures, addition of Cr to Hf-doped NiAl accelerated the a lumina scale growth rate and promoted spallation of the oxide scale. The re sults from initial detailed characterization indicate that rejection of chr omium at the metal-oxide interface gives rise to the formation of chromium- rich precipitates in the alloy, which apparently modify its oxidation behav ior. This suggests that for NiAl-based substrates, hot corrosion resistance and exceptional scale spallation resistance may be mutually incompatible g oals. (C) 2000 Elsevier Science B.V. All rights reserved.