Hot corrosion behavior of double ceramic layered CaZrO3/Yttria-stabilized zirconia coatings

A novel double ceramic layered (DCL) CaZrO3/Yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) was designed for improved service life against sulfate vanadate hot corrosion as compared with that of YSZ single layered coating. The hot corrosion behavior of DCL CaZrO3/YSZ coatings was studied at 950 degrees C after dry spreading 50%Na2SO4+50%V2O5 mixture onto a coated surface. The CaZrO3 as the topmost layer in DCL CaZrO3/YSZ coatings, served as a sacrificial layer during sulfate vanadate hot corrosion protecting the underneath YSZ coating. The corrosion reactions in this case were sluggish due to the initial formation of low melting point meta-calcium vanadate (CaV2O6) that isothermally transformed to higher melting point calcium vanadates having higher calcia (CaO) content. The corrosion reaction products sealed the top surface, impeding the oxygen movement and eventually retarded the thermally grown oxide (TGO) growth. The sulfate vanadate hot corrosion life of the DCL CaZrO3/YSZ coatings was observed to be more than double as compared with single ceramic layered YSZ coatings.