Journal
JOURNAL OF THE EUROPEAN CERAMIC SOCIETY
Volume 38, Issue 9, Pages 3333-3346Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.jeurceramsoc.2018.03.027
Keywords
EB-PVD alumina; 7YSZ; CMAS; Volcanic ash; Anorthite
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Funding
- German Science Foundation (DFG) [SCHU 1372/5-1]
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Al2O3 was deposited as a top coat on a standard 7YSZ layer (or layers) by means of EB-PVD technique and the corresponding morphology of the Al2O3/7YSZ coatings was studied in detail. This multi-layer TBC system was tested against calcium -magnesium-aluminium-silicate (CMAS) recession by performing infiltration experiments for different time intervals from 5 min to 50 h at 1250 degrees C using two types of synthetic CMAS compositions and Eyjafjallajokull volcanic ash (VA) from Iceland. The results show that the studied EB-PVD Al2O3/7YSZ coatings react quickly with CMAS or VA melt and form crystalline spinet (MgAl2-xFexO4) and anorthite (CaAI(2)Si(2)O(4)) phases. The presence of Fe-oxide in the CMAS has been found to be key element in influencing the spinel formation which was proved to be more efficient against CMAS sealing in comparison to the Fe-free CMAS compositions. Even though a rapid crystallization was assured, shrinkage cracks in the EB-PVD alumina layer produced during the crystallization heat treatment have proven to be detrimental for the CMAS/VA infiltration resistance. To overcome these microstructural drawbacks, an additional alumina deposition method, namely reaction-bonded alumina oxide (RBAO), was applied on top of EB-PVD Al2O3. RBAO acts as a sacrificial layer forming stable reaction products inhibiting further infiltration.
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