High-Temperature Corrosion of EB-PVD Yttria Partially Stabilized Zirconia Thermal Barrier Coatings with an Artificial Volcanic Ash Overlay
High-temperature interaction of 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) electron-beam physical vapor deposition (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 on short-term exposure of the EB-PVD YSZ coating to a small AVA load were moderate, in particular before 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.
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Document Type: Research Article
Affiliations: German Aerospace Center (DLR), Institute of Materials Research, 51170 Cologne, Germany
Publication date: March 1, 2011