Evaluation of the effectiveness of alkaline-earth metal oxides in inhibiting vanadium-induced hot corrosion of yttria-stabilized zirconia thermal barrier coatings (TBCs

Vanadium-induced hot corrosion is an accelerated high temperature corrosion of yttria stabilized zirconia (YSZ) ceramic topcoat in Thermal Barrier Coatings (TBCs) of gas turbine engines. It occurs due to YSZ interaction with fused vanadium salt that results from the usage of fuel contaminated with vanadium. The hot corrosion causes spallation and degradation of the topcoat due to reaction of yttria stabilizer (Y2O3) with the vanadium salt based on Lewis-acid mechanism and presence of molten acidic salts; and transformation of the yttria stabilized zirconia from tetragonal zirconia phase to monoclinic.;The use of alkaline earth-metal oxides (MgO and CaO) to inhibit vanadium-induced hot corrosion of YSZ has been investigated experimentally using powder and as-sprayed samples. Samples with alkaline-metal/vanadium-oxide molar concentrations of 1, 2, 3 and 5 were subjected to 900°C isothermal heating for up to 100hrs and subsequent cooling in laboratory air. Characterizations by colour spectrum, XRD, SEM, EDS and X-ray mapping analyses were carried out to estimate the phase distribution. Samples with low molar concentrations of 1 and 2 indicated degradation and destabilization of the 8YSZ within short period of heating while those with high molar concentration ratios showed inhibition effect of vanadium-induced hot corrosion. CaO showed better inhibition when compared to MgO of the same molar concentration to V2O 5. Samples with MgO/V2O5=5, CaO/V2O 5=3 and CaO/V2O5=5 molar concentrations displayed high inhibition efficiencies. The mechanism of inhibition is found to be consistent with Lewis-acid mechanism.