A comparative study on hot corrosion resistance of three types of thermal barrier coatings: YSZ, YSZ +Al_2O_3 and YSZ/Al_2O_3

摘要

Hot corrosion is one of the main destructive factors in thermal barrier coatings (TBC_S) 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 +Al_2O_3) and (c) layer composite of (YSZ/Al_2O_3) in which Al_2O_3 was as a topcoat on YSZ layer. Hot corrosion tests were carried out on the surface of coatings in molten salt (Na_2SO_4 + V_2O_5) at 1050 ℃ for 40 h. Spallation was observed in YSZ and (YSZ + Al_2O_3) coatings. The formation of monoclinic ZrO_2 and YVO_4 crystals as hot corrosion products caused the degradation of mentioned TBCs. Although monoclinic ZrO_2 decreased in (YSZ + Al_2O_3) in comparison with usual YSZ, dendritic YVO_4 crystals had main role in degradation of (YSZ + Al_2O_3) coating. Alumina coating as outer layer in YSZ/Al_2O_3 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/Al_2O_3.