Comparison of the corrosion resistance of Ni₂Al₃ coating with and without Ni-Re interlayer in dry and wet CO₂ gas

Ni₂Al₃ and Ni₂Al₃/Ni-Re coatings deposited on Fe-Cr-Ni alloy were oxidized in dry and wet CO₂ gas at 650 °C. Ni₂Al₃/Ni-Re coating shows higher oxidation resistance to both dry and wet CO₂ gas than Ni₂Al₃ coating. It is attributed to the retarding effect of Ni-Re interlayer on interdiffusion between Ni₂Al₃ out-layer and substrate, which inhibits the subsequent inner oxidation during corrosion. θ-Al₂O₃ is found in α-Al₂O₃ scales of both coatings during wet CO₂ corrosion. Water vapor accelerates the oxidation rate of both coatings in CO₂ gas by promoting the formation of the fast growing θ-Al₂O₃ on the surface.