Investigation of Degradation Behavior of Yttria Stabilized Zirconia Thermal Barrier Coatings in the Presence of Molten Sulfate-Vanadate Salt

The purpose of this study is investigation of hot corrosion behavior of plasma-sprayed yttria stabilized zirconia (YSZ) thermal barrier coatings in the presence of molten sulfate-vanadate salt. For this intention, NiCoCrAlY bond coat and followed by YSZ top coat were deposited on Inconel 738LC substrates by atmospheric plasma spraying (APS). Hot corrosion test was carried out on the surface of YSZ coating in the presence of salt mixture of Na2SO4 + V2O5 at 1000 °C for 30 h. To investigate hot corrosion behavior, microstructural characterization by scanning electron microscope (SEM), elemental analysis by energy dispersive spectroscopy (EDS) and phasic analysis by x-ray diffractometry (XRD) were done. Based on the results, reaction between molten salt and stabilizer of zirconia (Y2O3) and formation of YVO4 crystals, the detrimental phase transformation of zirconia from tetragonal to monoclinic due to depletion of stabilizer and finally creation of thermal and physical stresses was recognized to degradation mechanism of YSZ ceramic coatings in the presence of molten sulfate-vanadate salt.