Environmental Resistance of Pure and Alloyed γ′Ni₃ Al and β-NiAl^★

Hot corrosion behavior of pure and alloyed γ′-Ni₃Al (the major strengthening phase in Ni-base superalloys) and β-NiAl (the primary constituent of aluminide coatings) phases at 1600 F was investigated using burner rig tests. The results indicated that for exposure times greater than 100 hours, pure β-NiAl was more corrosion-resistant than γ′-Ni₃Al; for shorter times, the kinetics were found to be comparable. Corrosion of γ′-Ni₃Al was thus characterized by an incubation period of the order of 100 hours. Chromium was found to improve the hot corrosion resistance of NiAl considerably. Addition of Y to Cr-doped β-NiAl caused only modest additional improvements in corrosion resistance. In the case of γ′-Ni₃Al, Ta and Cr were found to markedly improve short-term hot corrosion performance, W appeared to be innocuous, whereas Ti definitely reduced its corrosion resistance.