Effect of water drops on the oxidation mechanisms of a ceria coated nickel-based superalloy

The effect of the addition of water drops on the oxidation mechanisms of ceria coatings generated by cathodic electrodeposition onto a Ni-based superalloy was studied for short isothermal tests (50 h) between 900 °C and 1100 °C. Correlations between the oxidation kinetics and the growth mechanisms of the oxide scales were drawn and compared to conventional aluminide coating. The phase transformations were highlighted using Raman micro-spectrometry in combination with X-ray diffraction and SEM–EDS. Delayed transformation of θ-Al2O3, the appearance of pores and spallation occurred onto aluminides and the chemical inertness of ceria and the critical role of pre-oxidation was demonstrated.

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► Influence of water drops on the oxidation and degradation mechanisms.
► Critical role of pre-oxidation during heat treatment to stabilize Al2O3 and crystallize ceria.
► Improved oxidation resistance of ceria-coated samples partly explained by the growth of CeAlO3.
► Adsorption and release of water molecules but no dissociation due to ceria chemical stability.
► Spallation due to delayed transformation of theta-alumina onto aluminides with water drops.