Hot corrosion behavior of CoCrNiAlY-YSZ-RSZ dual-ceramic thermal barrier coating with Al plating in molten sulfate mixture

A novel Al plating layer was deposited on the CoCrNiAlY-YSZ-RSZ dual ceramic thermal barrier coating. The hot corrosion behaviors of these coatings in molten sulfate mixture were studied by the detail characterizations. This coating without Al plating possessed a fast mass gain trend, severe elemental diffusion and rapid TGO growth during the hot sulfate exposure, resulting in a significant increase in mass gain from 6.12 mg/cm2 at 20 h to 13.67 mg/cm2 at 100 h and aggravated coating fracture. In comparison, a continuously dense Al2O3 barrier layer formed on the coating's surface, preventing or delaying the infiltration of the molten sulfate and oxygen, and eventually led to an enhanced corrosion resistance. This coating with Al plating showed a slight mass gain from 8.20 mg/cm2 at 20 h to 9.31 mg/cm2 at 100 h, but also exhibited very slow TGO growth and stable structure. The potential molten sulfate corrosion mechanisms of these coatings with and without Al plating were systematically discussed.