Hot corrosion control in plasma sprayed YSZ coating by alumina layer with evaluation of microstrcuture and nanoindentation data (H, E)

Abstract

Thermal barrier coatings (TBCs), which contain yttria stabilized zirconia (YSZ) are used as thermal insulation coatings on hot section components in gas turbine in order to increase operation temperature for higher efficiency. 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 two types of plasma sprayed TBCs was evaluated: a) usual YSZ (yttria stabilized zirconia) and b) layer composite of (YSZ/Al2O3) in which Al2O3 was as a top coat 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 coating due to formation of monoclinic ZrO2 and YVO4 crystals as hot corrosion products. 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. Also nanoindentation tests demonstrated that the hardness (H) and elastic modulus (E) of the usual TBC increased substantially after hot corrosion whereas these properties exhibited the less variations in YSZ/Al2O3.