Investigation of electrochemical corrosion behavior of CoNiCrAlY bond coat and Yttria Stabilized Zirconia thermal barrier coatings

Thermal barrier coating (TBC) systems have been widely employed on a variety of value added components particularly in defence, aviation, aircraft and aerospace industries. TBCs provide thermal insulation on critical engine components of gas turbine engines such as turbine blades that are subjected to high temperatures. Cold gas dynamic spraying (CGDS) technique is a recently developed innovative coating technique that allows deposition of dense and oxide-free metallic coatings. In this study, approximately 100 μm thick metallic based bond coats with CoNiCrAlY content were deposited on Inconel 718 superalloy substrate material using CGDS technique. Afterwards, ZrO2 + Y2O3 (YSZ) ceramic top coatings with approximate thickness of 300 μm were deposited on the CoNiCrAlY bond coats with atmospheric plasma spray (APS) technique to produce the TBC system. Electrochemical corrosion tests of the TBC systems consisting of the substrate material, metallic bond coat and ceramic top coat were performed. Corrosion tests were performed in 0.1 M sodium chloride (NaCl) solution at room temperature using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) experiments. A three electrode electrochemical corrosion test cell consisting of graphite rod as the counter electrode, Ag/AgCl as the reference electrode, and the samples as the working electrode, was used. Microstructural and surface analyses of the TBC system comprising of the substrate, metallic bond coat and ceramic top coat were performed before and after the electrochemical tests, and an indepth comparison of the obtained results with the related literature.