A comparative study on hot corrosion resistance of three types of thermal barrier coatings: YSZ, YSZ + Al2O3 and YSZ/Al2O3

Hot corrosion is one of the main destructive factors in thermal barrier coatings (TBCs) which comes as a result of molten salt effect on the coating–gas interface.Hot corrosion behavior of three types of plasma sprayed TBCs was evaluated: (a) usual YSZ (yttria-stabilized zirconia), (b) particle composite of (YSZ + Al2O3) and (c) layer composite of (YSZ/Al2O3) in which Al2O3 was as a topcoat on YSZ layer. Hot corrosion tests were carried out on the surface of coatings in molten salt (Na2SO4 + V2O5) at 1050 °C for 40 h. Spallation was observed in YSZ and (YSZ + Al2O3) coatings. The formation of monoclinic ZrO2 and YVO4 crystals as hot corrosion products caused the degradation of mentioned TBCs. Although monoclinic ZrO2 decreased in (YSZ + Al2O3) in comparison with usual YSZ, dendritic YVO4 crystals had main role in degradation of (YSZ + Al2O3) coating. Alumina coating as outer layer in YSZ/Al2O3 reduced the penetration of molten salt into YSZ and resulted in the further resistance of TBC against hot corrosion, because the hot corrosion products considerably decreased in YSZ/Al2O3.