Al-nitrate surface modification for hot-corrosion-resistant YSZ coatings

Hot corrosion caused by vanadium- and sulfate-containing molten deposits is a major degradation mechanism of yttria-stabilized zirconia thermal barrier coatings (YSZ-TBCs) in gas-turbine environments. In this study, water-based nitrate precursor treatments were applied to YSZ-TBC-coated Inconel 738LC substrates using a flame-assisted spray process under burner-rig conditions. An Al-based precursor system (Water AN2) was evaluated under both static V ₂ O ₅ exposure and cyclic simulated hot-corrosion environments. Exposure to molten V ₂ O ₅ at 1000 °C for 10 h caused severe delamination of the as-received YSZ-TBC specimen, whereas the Water AN2-treated specimen maintained coating integrity. During cyclic hot-corrosion testing using a V ₂ O ₅ –Na ₂ SO ₄ –NiSO ₄ corrosive solution, the precursor-treated specimen exhibited delayed degradation, smaller mass variation, and reduced growth of needle-like corrosion products. SEM observations revealed substantially reduced corrosion-product density and crystal growth on the precursor-treated surface, while EDS analysis confirmed the formation of vanadate-related corrosion products under the test conditions. In addition, stable spray operation was maintained throughout the treatment process without nozzle clogging. The results demonstrate that water-based nitrate precursor treatment delays degradation and suppresses corrosion-product growth in YSZ-TBC systems exposed to severe vanadate hot-corrosion environments. The approach requires no modification of the underlying coating architecture and provides a practical route for improving coating durability in gas-turbine applications.