CMAS degradation of ytterbium aluminum garnets

The degradation of ytterbium aluminum garnet (YbAG) exposed to molten Ca–Mg–Fe–Al–Si–O (CMAS) at 1673 K was investigated for two kinds of dense polycrystalline YbAG with compositions deviating slightly from stoichiometry, referred to as Al‐ and Yb‐rich. The mitigation of the CMAS attack for Yb‐rich...

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Bibliographic Details
Published in:Journal of the American Ceramic Society 2023-08, Vol.106 (8), p.4863-4876
Main Authors: Kitaoka, Satoshi, Tanaka, Makoto, Kawashima, Naoki, Ito, Taishi, Yokoe, Daisaku, Kato, Takeharu, Ogawa, Takafumi, Yamazaki, Naoki, Hosoya, Nagisa, Nakamura, Takeshi
Format: Article
Language:English
Subjects:
Aluminum
Cations
CMAS
core–shell
Degradation
Dissolution
environmental barrier coatings
garnet
Garnets
Grain boundaries
Iron
Magnesium
Silicon
solid solution
Stoichiometry
Thin walled shells
Ytterbium
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Summary:The degradation of ytterbium aluminum garnet (YbAG) exposed to molten Ca–Mg–Fe–Al–Si–O (CMAS) at 1673 K was investigated for two kinds of dense polycrystalline YbAG with compositions deviating slightly from stoichiometry, referred to as Al‐ and Yb‐rich. The mitigation of the CMAS attack for Yb‐rich YbAG was markedly superior to that for the Al‐rich one. For both types of YbAG, corrosion progressed due to the preferential penetration of the CMAS melt along grain boundaries in the thickness direction and the simultaneous dissolution of crystal grains into the melt. The lower of the corroded region consisted of YbAG crystals with a core/shell‐I/shell‐II structure. Shell‐I contained alkaline earth, silicon, and iron cations, whereas these cations were hardly detected in shell‐II. Growth of the shell‐I region was considered to progress by dissolution and reprecipitation through the melt existing around it, and finally, the melt disappeared, resulting in the formation of a thin shell‐II region containing little of these ions. The formation and growth of the shell‐I region were found to be promoted by making the YbAG Yb‐rich, resulting in enhancement of the resistance to CMAS. In the reactions of Yb‐ and Al‐rich YbAG EBCs with CMAS, corrosion progressed due to preferential penetration of the CMAS melt along grain boundaries (GBs) and simultaneous dissolution of crystal grains. The liquids solidified to create core–shell structures that enhanced CMAS resistance.
ISSN:0002-7820
1551-2916
DOI:10.1111/jace.19110