Hot Corrosion Behavior of Intermetallic Compounds of Ni-Al System in Fused 75% Na₂SO₄-25% NaCl Salt

Abstract

Hot corrosion behavior of intermetallic compounds NiAl, Ni₃Al, Ni₃(Al, Ti) and NiAl+Cr in a fused 75% Na₂SO₄-25% NaCl salt has been investigated in the temperature range from 700° to 1 000°C in comparison with that of Ni and Ni-base superalloy IN-738LC.
The results obtained are as follows :
(1) The corrosion loss in weight of Ni₃Al and Ni₃(Al, Ti) is much larger than that of NiAl, Ni and IN738LC. For NiAl and IN-738LC, the peak of corrosion loss is observed at 800°C.
(2) Oxide layers such as α-Al₂O₃ and Cr₂O₃ formed on the surface of NiAl and IN-738LC above 850°C cause a decrease of corrosion loss. These oxides, however, are not protective completely, and the internal degradation such as oxidation and sulfidation is observed.
(3) On the surface of NiAl+ (2040) % Cr, α-Al₂O₃ forms even at a low temperature (700°C) and restrains the permeation of the fused salt especially the sulfur into the specimens so that the corrosion loss and the internal degradation is reduced.