Influence of the oxide scale features on the electrochemical descaling and stripping of aluminide coatings

Turbine components are subjected to very aggressive environments at high temperatures leading to corrosion and/or oxidation. Because of their high cost, they have to be repaired instead of being replaced. Prior to refurbishment and recoating, the components have to be fully stripped to remove the oxide products and defective coatings. In this work, an electrochemical stripping method is studied. Cathodic polarization induced the hydrogen evolution reaction (HER) to remove the scales while switching to anodic polarization dissolved the aluminide coating underneath. The influence of oxides on this method is investigated. The effect of grit blasting steps on the dissolution reactions was also evaluated. It will be shown that the most effective stripping can be performed in presence of non-continuous oxides, such as spinel NiAl2O4, rather than compact oxides such α-alumina. In the latter, a prior grit blasting step allows activation of the sample surface. The dissolution mechanisms of the coatings are finally discussed after the solution was able to go through the oxide scales. (a) Electrochemical stripping (potentiostatique mode) of aluminide coatings allows controlled dissolution in the absence of oxide scales. (b) Initial hydrogen bubbling removes the scale and stripping of the aluminide follows. [Display omitted] •Selective electrochemical removal of aluminide coatings investigated•Influence of oxide scales on the removal elucidated•Hydrogen evolution reaction unable to remove adherent alumina scales•Dissolution kinetics slowed down with the decrease of Al content in the coatings.