Alloying Effects of Cr and Re on the Hot-corrosion of Nickel-based Single Crystal Superalloys Coated with a Na₂SO₄-NaCl Salt

Abstract

The alloying effect of chromium and rhenium was investigated on the hot-corrosion resistance of nickelbased single crystal superalloys. Using a conventional thermo-gravimetric method, hot-corrosion resistance to the Na₂SO₄-NaCl salt environment was measured with a variety of alloys, Ni-(916)mol%Cr-12 mol%Al-(1.22.0)mol%Ti-(1.12.7)mol%Ta-(1.23.8)mol%W-(01.0)mol%Mo-(01.0)mol%Re.
Hot-corrosion resistance was shown to be improved significantly with increasing chromium content in the alloys. For example, a hot-corrosion index which was defined as the weight gain of the specimen exposed for 72 ks to the salt, was reduced to nearly nil in the 16 mol% Cr alloys. This result was interpreted as due to the existence of a corrosion product layer containing Cr, Al, Ni, O and S. This layer formed in the interface between the base alloy and the salt was very efficient in suppressing the hot-corrosion due to a basic-fluxing mechanism. Similarly, it was found that the addition of a small amount of rhenium up to 0.40.5 mol% could improve hot-corrosion resistance remarkably.