Evaluation of microstructural evolution of thermal barrier coatings exposed to Na2SO4 using impedance spectroscopy

Impedance spectroscopy as a non-destructive evaluation technique was employed to study the microstructural evolution of thermal barrier coatings exposed to Na2SO4 at 950 °C. The results showed that the resistance and capacitance of yttria-stabilized zirconia top coat increased with corrosion time. The resistance of thermally growth oxide (TGO) from 20 to 60 h decreased slowly, which indicates there is little change in the composition of TGO. The fast decrease in the resistance of TGO from 60 to 100 h may correspond to the compositional change of TGO from a-Al2O3 to more conductive NiO and Ni(Cr, Al)2O4 with corrosion time.

Research highlights
► Microstructural evolution of TBC under hot corrosion environment was studied using IS.
► Resistance and capacitance of the YSZ top coat increase with hot corrosion time.
► Resistance of TGO is more sensitive to compositional change under Na2SO4 environment.