Study of the Degradation of Duplex Coating Systems Al2O3–13% TiO2 / NiCoCrAlY Thermal-spray by Atmospheric Plasma and Exposed to Isothermal Oxidation

The present work aims to study the degradation of Al2O3–13% TiO2 / NiCoCrAlY duplex coating systems thermo-sprayed by atmospheric plasma and exposed to isothermal oxidation. To carry out the proposed objectives, ASTM A36 steel specimens were tested, where the duplex coating system was designed, which underwent an isothermal oxidation heat treatment at 850 oC and by Electrochemical Impedance Spectroscopy (EIS) in a solution, 3,5 % NaCl, the effect of oxidationtime on the electrochemical response of the system was evaluated, through the interpreting Bode and Nyquist diagrams, for which several Equivalent Electric Circuits proposed according to various authors were modeled. Subsequently, the morphological and microstructural characterization was carried out using Optical Microscopy, Scanning Electron Microscopy and EDX, the measurements of the thicknesses of the two layers mentioned above were also taken and the percentage of porosity present for the conditions before and after oxidation was calculated. Comparing the results obtained, to permanence times of 72 hours it was observed the formation of TGO, composed of a mixture of Cr and Al oxide. It was also confirmed that the samples exposed to said time presented an increase in the impedance module due to the fact that the TGO penetrates the open pores of the coating, the decrease in the percentage of porosity was also evidenced after oxidationheat treatment.