Abstract
Thermal barrier coatings (TBCs) deposited either by air plasma spray (APS) or electron beam physical vapor deposition (EB-PVD) provides thermal insulation to the superalloy blades and vanes. The durability and reliability of TBCs play an important role in the service reliability and durability of hot-section components in advanced turbine engines. Development of non-destructive evaluation (NDE) techniques for quality control, lifetime monitoring and lifetime prediction of TBCs have been the focus of research for designers, manufacturers and users of the advanced turbine engines. In this work, electrochemical impedance spectroscopy (EIS) has been used as a NDE technique to evaluate the varying microstructure and chemistry of as-coated TBCs. EIS were acquired at the corrosion potential for TBCs with varying thickness, microstructure and chemistry using 0.01 M [Fe(CN)6]–3/ [Fe(CN)6]-4·3H2O electrolyte solution. Equivalent circuits corresponding to the multiplayer constituents of TBCs were then correlated to the experimental EIS data. Resistance and capacitance of various components in TBCs can provide useful information regarding the microstructure and chemistry as-coated TBCs.
