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 spinet NiAl2O4, rather than compact oxides such alpha-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. (C) 2016 Elsevier B.V. All rights reserved.