Impedance spectroscopy study of plasma sprayed and EB-PVD thermal barrier coatings

Impedance spectroscopy (IS) and SEM/EDX were used to characterise a range of isothermally heat-treated plasma sprayed (PS) and electron beam physical vapour deposited (EB-PVD) thermal barrier coatings (TBCs). Nyquist (imaginary (Z″) vs. real (Z′) impedance) and Bode plots (phase angle (θ) vs. frequency (f)) were used to investigate the effect of variation of Ag electrode size on electrical responses, and to compare PS and EB-PVD TBCs. Various observed electrical responses relating to the Ag electrode size effect, the thickness, continuous nature and purity of the TGO layer, and YSZ coating thickness, were explained using Circuit modelling.