Accelerated Oxidation of Single Crystal Ni-10Cr-12Al-Ta-W Superalloys Coated with a Na₂SO₄-NaCl Salt

Abstract

The behavior of the accelerated oxidation in a Na₂SO₄-NaCl salt was investigated for nickel-based single crystal superalloys for turbine blades and the other applications. In particular, attention was directed towards the tungsten effect on the oxidation behavior. For this purpose, several alloys with varying tungsten contents were prepared for a Ni-10Cr-12Al-W-Ta system. The accelerated oxidation curves were obtained using a thermo-balance and the corrosion products were identified by EPMA and a conventional X-ray diffraction method. As the tungsten content increases, the oxidation curves became complicated and showed poor hot-corrosion resistance. It was found from the identification of the corrosion products that the accelerated oxidation occurred in this alloy system by a mixed mechanism of the basic-and the acidic-fluxing. Furthermore, it was suggested that the amount of a precipitated α-W phase could be a measure for the hot-corrosion of these alloys coated with a Na₂SO₄-NaCl salt.