High-temperature infiltration behavior and phase stability of yttria-stabilized zirconia (7YSZ) thermal barrier coatings (TBC) produced by atmospheric plasma spray interacting with volcanic ashes (VAs) are presented here. Three VAs from the Colima, Popocatepetl, and Eyjafjallajökull volcanoes have been used in this work. Previous to infiltration experiments, physicochemical characterization of the VAs was carried out including thermal analyses by DSC, structural studies by XRD, and ICP chemical composition measurements. TBCs' infiltration tests were carried out at 1250 °C for different times. Results showed that infiltration depth as a function of time behaves in a non-linear way. Mainly two important infiltration behaviors were identified corresponding to high-and slow-speed infiltration regimes. Higher infiltration kinetics was detected for VAs with lower SiO 2 content. The extent of chemical degradation of the 7YSZ is directly related to the silica content. For greater SiO 2 values, a higher content of monoclinic ZrO 2 was observed leading to maximum values at intermediate annealing times between 2 and 5 h. This behavior can be correlated with the high-speed tetragonal to monoclinic ZrO 2 transformation at short times (between 2 and 5 h) until a maximum monoclinic content is reached. After that, the reaction follows by the interplay of ZrSiO 4 formation at the expense of previously formed m-ZrO 2 together with the incorporation of Y and Zr to the glass melt.
Molten calcium-magnesium-aluminum-silicate (CMAS) mineral particles cause significant degradation of thermal barrier coatings (TBCs) in aero-engines. One approach to protect the TBC coating against the CMAS attack is the application of a sacrificial coating on top of the TBC coating. In this work sacrificial Al 2 O 3 coatings were deposited on top of EB-PVD 7YSZ layers using suspension thermal spraying starting from an aqueous Al 2 O 3 suspension. Spray parameters were varied in order to produce sacrificial topcoats with two different microstructures and porosities levels. The coating systems were tested under CMAS attack by performing shortand long-time infiltration tests at 1250 °C. It was found out that the porosity and morphology of Al 2 O 3 coatings strongly influenced the CMAS infiltration kinetics and the formation of various phases. CMAS mitigation depended on the interaction between the coating morphology which rules the driving force for infiltration, as well as on the reaction speed between alumina and the CMAS deposit.
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