Impermeable CeO2 overlay for the protection of plasma sprayed YSZ thermal barrier coating from molten sulfate-vanadate salts

Abstract

Yttria stabilized Zirconia thermal barrier coatings with around 200 μm overlay of Al2O3 and CeO2 were deposited on Inconel substrate using atmospheric plasma spray technique. Hot corrosion tests were carried out on the thermal barrier coating in molten salt mixtures (45 wt% Na2SO4 + 55 wt% V2O5) at 1150 °C for 30 h. Although the YSZ and Al2O3/YSZ coatings were gradually degraded by the infiltration of the molten salt, the CeO2/YSZ coatings remarkably restrained the infiltration of the molten salt into the YSZ coating. For the YSZ coating without any overlay, the YSZ reacted with V2O5 to form YVO4 during exposure to the molten salt, leading to the formation of a large amount of monoclinic phase of ZrO2 due to the leaching of Y2O3 from YSZ. For the Al2O3/YSZ coating, the Al2O3 overlay reduced the rigorous infiltration of the molten salt, which caused in lesser amount of leaching of Y2O3 from YSZ. However, for the CeO2/YSZ coatings, CeO2 not only physically prevented the molten salt infiltration, but also completely reacted with V2O5 to form CeVO4 and completely restrained the infiltration of the molten salt into the YSZ coating. Additionally, the Al2O3/YSZ and CeO2/YSZ showed 17% and 52% increase in thermal shock resistance respectively compared to YSZ coating.