Degradation mechanism of Ni based Al plasma spray coatings in molten sulfate salts

Abstract

The anodic polarization and AC impedance measurements were conducted in 50mol %Na₂SO₄,-50mol %Li₂SO₄ molten sulfates for Ni based Al plasma spray coatings at 923-1073K. It was found that the corrosion resistance of Ni based Al plasma spray coatings was very poor. The results obtained from polarization measurement were well correlated with that from AC impedance monitoring. SEM observation showed that accelerated corrosion occurred between coating layer and the Ni substrate. The existence of sulfur was confirmed at coating layer/Ni substrate interface by EDX analysis. The degradation mechanism of Ni baseｄ Al plasma coatings was discussed.