Abstract
A 25 μm thick dense and continuous Al 2O 3 overlay has been deposited on the outer surface of the yttria-stabilized zirconia (YSZ) coating by electron-beam physical vapor deposition. Hot corrosion tests were carried out on the thermal barrier coating (TBC) with and without an Al 2O 3 coating in molten salt mixtures (Na 2SO 4+5%V 2O 5) at 950 °C for 100 h. Although the Al 2O 3 overlay was gradually degraded by the formation of low-melting liquid phase during exposure to the molten mixture of sulphate and vanadate, it remarkably restrained the infiltration of the molten salt into the YSZ coating. For the YSZ coating without the Al 2O 3 overlay, the YSZ reacted with V 2O 5 to form YVO 4 during exposure to the molten salt, leading to the formation of a large amount of M-phase of ZrO 2 due to the leaching of Y 2O 3 from YSZ. In contrast, the amount of M-phase in the TBC coating with Al 2O 3 overlay was substantially reduced.
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