IMPERMEABLE THIN AL2O3 OVERLAY FOR TBC PROTECTION FROM SULFATE AND VANADATE ATTACK IN GAS TURBINES [electronic resource].

Published:: Washington, D.C. : United States. Dept. of Energy, 2002.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy.
Physical Description:: 14 pages : digital, PDF file
Additional Creators:: United States. Department of Energy and United States. Department of Energy. Office of Scientific and Technical Information

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Summary:

In order to improve the hot corrosion resistance of conventional YSZ TBC system, a dense and continues overlay of Al₂O₃ coating of about 25 {micro}m thick was deposited on the surface of TBC by EB-PVD and high velocity oxy-fuel (HVOF) spray techniques. Hot corrosion tests were carried out on the TBC with and without Al₂O₃ coating in molten salts mixtures (Na₂SO₄ + 5% V₂O5) at 950 C for 10h. The microstructures of TBC and overlay before and after exposure were examined by means of scanning electron microscopy (SEM), energy-dispersive X-ray spectrometer (EDX), X-ray diffraction (XRD) and secondary ion mass spectrometry (SIMS). It has been found that TBC will react with V₂O₅ to form YVO₄. A substantial amount of M-phase of ZrO₂ was formed due to the leaching of Y₂O₃ from YSZ. During hot corrosion test, there were no significant interactions between overlay Al₂O₃ coating and molten salts. After exposure, the alumina coating, especially produced by HVOF, was still very dense and cover the surface of YSZ, although they had been translated to α-Al₂O₃ from original γ-Al₂O₃. As a result, Al₂O₃ overlay coating decreased the penetration of salts into the YSZ and prevented the YSZ from the attack by molten salts containing vanadium. Accordingly, only a few M-phase was formed in YSZ TBC, compared with TBC without overlay coating. The penetration of salts into alumina coating was thought to be through microcracks formed in overlay Al₂O₃ coating and at the interface between alumina and zirconia due to the presence of tensile stress in the alumina coating. In the next year, we will study the mechanisms of cracking of the overlay Al₂O₃ layer. The hot corrosion test of TBC with EB-PVD deposited Al₂O₃ coating will be again performed. However before hot corrosion tests, the post-annealing will be carried out in vacuum (residual pressure 10⁻³ Pa) at 1273K for 1h in order to transform the as-sputtered Al₂O₃ overlay to crystalline α-Al₂O₃ overlay. The effect of thickness of Al₂O₃ coating on hot corrosion resistance will also be investigated. We will prepare Al₂O₃ coating by sol-gel method. The corrosion resistance of TBC with sol-gel Al₂O₃ coating will be determined and discussed with the results of TBC with EB-PVD and HVOF Al₂O₃ coating.

Report Numbers:

E 1.99:fc26-01nt41189--04
fc26-01nt41189--04

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Note:

Published through SciTech Connect.
08/31/2002.
"fc26-01nt41189--04"
Scott X. Mao.
National Energy Technology Lab., Pittsburgh, PA (US)
National Energy Technology Lab., Morgantown, WV (US)

Type of Report and Period Covered Note:

Topical; 09/01/2001 - 08/31/2002

Funding Information:

FC26-01NT41189

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