Corrosion mechanism of a NiCoCrAlTaY coated Mar-M247 superalloy in molten salt vapour

Abstract

A mechanism of corrosion is proposed relating to a NiCoCrAlTaY coated Mar-M247 superalloy exposure in molten Na2SO4 salt vapour at 900°C. The corrosion process indicates the parabolic “diffusion controlled” region I at rate of 4.6×10−6mg2cm−4s−1, the combination of parabolic and linear “reaction–diffusion controlled” region II at rate of 2.28×10−5mg2cm−4s−1 and 4.35×10−5mgcm−2s−1, and finally the complete “reaction controlled” region III at the same rate of 3.92×10−4mgcm−2s−1 as the uncoated superalloy. The corrosion kinetics of each region and of the whole process are formulated rationally associated with the corrosion mechanism.