Evaluation of TGO growth in thermal barrier coatings using impedance spectroscopy

Impedance spectroscopy was employed to evaluation of TGO growth on the interface of YSZ/bond coat in plasma sprayed thermal barrier coatings during isothermal oxidation and exposed to Na2SO4 at 950 degrees C. Various observed electrical responses relating to the thickness, continuous nature and purity of the TGO layer were explained using an equivalent circuit model. The results show the thickness of TGO increases with exposure time. The TGO after isothermal oxidation mainly contains Al2O3. However, the TGO after hot corrosion changes gradually from Al2O3 to a mixture of NiO, Al2O3 and Ni(Cr, Al)(2)O-4 spinel. The thickness of the continuous alumina layer formed in TBCs can be evaluated by electrical modulus spectra.