Effect of Al_2O_3 Overlay on Hot-Corrosion Behavior of Yttria-Stabilized Zirconia Coating in Molten Sulfate-Vanadate Salt

摘要

A 25?m 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 percent V_2O_5) at 950 deg C for 100 hours. 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.