Optimizing Alumina Integration in Yttria-Stabilized Zirconia Thermal Barrier Coatings for Improved Moisture Resistance in Hydrogen-Enriched Flame

Abstract The addition of a 100 nm-thick alumina layer to conventional yttria-stabilized zirconia thermal barrier coatings could offer enhanced moisture resistance. The effects of thickness and location of the alumina layer, deposited via atomic layer deposition, on the moisture resistance properties of yttria-stabilized zirconia coatings are examined. These coatings were synthesized with alumina layers of varying thicknesses (100 nm, 350 nm, and 550 nm), deposited either on top of or beneath the yttria-stabilized zirconia layer. These coatings were exposed to a hydrogen-enriched flame containing 35.9% moisture at 1143−1170 °C temperature in a distributed swirl combustor, for time durations of 15 and 30 min. Thermal mismatch-induced crack lines were observed in the yttria-stabilized zirconia coating alone and the yttria-stabilized zirconia coating with an alumina layer on top. However, the yttria-stabilized zirconia coating with an alumina layer beneath exhibited radial cracks. It was also observed that higher moisture content and prolonged testing time resulted in thicker interfacial oxide layers for all coating samples. The effects of alumina layer thickness differed between samples with alumina on top of the yttria-stabilized zirconia and those with alumina beneath it. When alumina was placed beneath the yttria-stabilized zirconia, the interfacial layer growth initially decreased with increasing alumina thickness but later increased due to interconnected crack formation. In contrast, top-layer alumina exhibited a more consistent barrier effect, with 350 nm and 550 nm alumina layers limiting interfacial growth to below 10 nm even after 30 min of exposure.