High-temperature corrosion of EB-PVD yttria partially stabilized zirconia thermal barrier coatings with an artificial volcanic ash overlay

Kurzfassung

High-temperature interaction of a sol-gel derived artificial volcanic ash (AVA) matching the bulk composition of the April 15, 2010 Eyjafjallajokull (Iceland) volcanic eruption with a standard 4 mol-% (7 wt-%) Y2O3-stabilized ZrO2 (YSZ) EB-PVD thermal barrier coating and a corresponding YSZ powder is investigated in order to access possible implications of similar volcanic ashes on the performance of coated turbine engine airfoils. Up to 900°C AVA deposits and EB-PVD YSZ do not show significant interaction. Viscous flow above the glass transition of AVA (Tg ~ 930 °C) yields proceeding wetting of EB-PVD YSZ coatings. At 1100 °C, the YSZ surface is covered by a dense glaze-like AVA overlay. At 1200 °C AVA is mostly infiltrating the coating, leaving a crystalline plagioclase- and hematite-type residue at the interface. Moreover, some ZrSiO4 is formed at the expense of YSZ. The overall thermochemical effects upon short-term exposure of the EB-PVD YSZ coating to a small AVA load were moderate, in particular prior to complete infiltration. On the other hand, AVA acts as a solvent for the stabilizing Y2O3 beyond 1000 °C and a progressive depletion of Y2O3 in the YSZ is observed at the AVA / YSZ interface. Detrimental effects on YSZ phase stability and hence coating lifetime cannot be ruled out for long-term exposure and higher AVA loads.