Increasing the hot-corrosion resistance of thermal barrier coating systems by the addition of oxides of Cr and Mg

Abstract

<p>The hot corrosion of model thermal barrier coating (TBC) systems was studied at 9000C using either Na2SO4 or Na2SO4-CaSO4-MgSO4 eutectic as the corrosive salt. The yttria-stabilized zirconia (YSZ) top coat was deposited via air plasma spraying and the top coat modification methods investigated involved (1) infiltration with aqueous solutions of water-soluble compounds of chromium (e.g., chlorides, nitrates, acetates) and alkaline earth elements (e.g., MgCrO4·xH2O) followed by an oxidizing conversion treatment and (2) co-depositing Cr2O3 with the YSZ. The goal of these modifications was to deliver alkaline earth and/or chromium oxides for reaction with the molten salt, thereby inhibiting its penetration through the top-coat and/or its reactivity with the substrate alloy. It was found that these modifications could have a favorable effect on the chemistry of the salt and the hot-corrosion resistance of the TBC system. It was further found that the corrosiveness of a given salt was very dependent on the type of test conducted, i.e., thin-film pre-deposit of the salt onto the sample or submersion of the sample into molten salt.</p>