Effects of Atomic Layer Deposition-Alumina on Moisture Resistance Properties of Yttria-Stabilized Zirconia Thermal Barrier Coatings in Hydrogen Enriched Flame

Abstract Current thermal barrier coatings (TBCs), typically made of yttria-stabilized zirconia (YSZ), face challenges in the high-moisture, high-temperature environment during the combustion of hydrogen-enriched fuels. This is mainly due to YSZ's high ionic conductivity facilitating moisture transfer through the YSZ layer toward the underlying substrate. In this study, a thin alumina layer, deposited by atomic layer deposition (ALD), was added to the YSZ coating, and the effect of the ALD-alumina layer on the moisture resistance properties of YSZ coatings was investigated in the hydrogen-enriched flame zone of a swirl combustor. Three different coating configurations were prepared: YSZ-alone, YSZ with an alumina layer beneath it (YSZ/alumina), and YSZ with an alumina layer on top (alumina/YSZ). At 430 °C, the ionic conductivity of the YSZ/alumina and alumina/YSZ coatings was measured to be 4.33×10−6Sm−1 and 1.34×10−7Sm−1, respectively, which was 4–5 orders of magnitude lower than that for the YSZ coating. These coatings were tested in the flame zone with a temperature of 1248–1260 °C and a moisture concentration of about 18.1% for 15 min in the swirl combustor. Compared to the baseline YSZ-alone coating, the growth in thickness of the interfacial oxidation layer near the substrate was reduced by a factor of >2 for the YSZ/alumina coating and by a factor of >8 for the alumina/YSZ coating. The result showed that the thin ALD-alumina layer effectively acted as a barrier to moisture diffusion, primarily due to its extremely low ionic conductivity.