PHASE EVOLUTION UPON AGEING OF AIR-PLASMA SPRAYED t'-ZIRCONIA COATINGS. PT.1. SYNCHROTRON X-RAY DIFFRACTION

Phase evolution accompanying the isothermal ageing of free-standing air-plasma sprayed (APS) 7-8 wt% yttria-stabilised zirconia (8YSZ) thermal barrier coatings (TBCs) is described. Ageing was carried out at temperatures ranging from 982 C to 1482 C in air. The high-temperature kinetics of the phase...

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Bibliographic Details
Published in:Journal of the American Ceramic Society 2013-01, Vol.96 (1), p.290-298
Main Authors: Lipkin, D M, Krogstad, J A, Gao, Y, Johnson, C A, Nelson, W A, Levi, C G
Format: Article
Language:English
Subjects:
Aging
Ceramics
Coatings
Deposition
Evolution
Phase transformations
Synchrotrons
Yttria stabilized zirconia
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Summary:Phase evolution accompanying the isothermal ageing of free-standing air-plasma sprayed (APS) 7-8 wt% yttria-stabilised zirconia (8YSZ) thermal barrier coatings (TBCs) is described. Ageing was carried out at temperatures ranging from 982 C to 1482 C in air. The high-temperature kinetics of the phase evolution from the metastable t' phase into a mixture of transformable Y-rich (cubic) and Y-lean (tetragonal) phases were studied using ambient temperature XRD. A Hollomon-Jaffe parameter (HJP), T[27 + ln(t)], was used to satisfactorily normalise the extent of phase decomposition over the full range of times and temperatures. Comparison to vapour deposited TBCs reveal potential differences in the destabilisation mechanism in APS coatings. Furthermore, the lattice parameters extracted from Rietveld refinement of the XRD patterns were used to deduce the stabiliser concentrations of the respective phases, which suggest a retrograde tetragonal solvus over the temperature range studied. Together with a complementary microstructural study presented in Part 2, this effort offers new insights into the mechanisms governing the phase evolution and raises implications for the high-temperature use of 8YSZ ceramics.
ISSN:0002-7820