Effect of Al2O3 overlay on hot-corrosion behavior of yttria-stabilized zirconia coating in molten sulfate-vanadate salt

Abstract A 25 μm thick dense and continuous Al 2 O 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 2 O 3 coating in molten salt mixtures (Na 2 SO 4 +5%V 2 O 5 ) at 950 °C for 100 h. Although the Al 2 O 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 2 O 3 overlay, the YSZ reacted with V 2 O 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 2 O 3 from YSZ. In contrast, the amount of M-phase in the TBC coating with Al 2 O 3 overlay was substantially reduced.