Investigation of oxidation behaviour of thermal barrier coatings (TBC) with differing top coating contents

Thermal Barrier Coatings (TBCs) is the coating type commonly preferred in aerospace and aircraft industry for critical region parts exposed to high temperatures such as the combustion chambers of gas turbine motors and turbine blades as a means for thermal insulation. TBCs provide protection to minimize aggressive environmental conditions such as oxidation, corrosion and thermal shock occurring at high temperatures within the structure. In this study, CoNiCrAlY metallic bond coat was deposited on Inconel 718 superalloy substrate material with a thickness about 100 μm using Atmospheric Plasma Spray (APS) method. Production of TBCs was accomplished with deposition of ZrO2+Y2O3 (YSZ) and ZrO2+MgO respectively, as two different ceramic top coating materials, having a total thickness of 300 μm. The specimens were subjected to metallographic investigation before the oxidation test, their surface roughness, porosity, hardness and microstructural properties were investigated and then compared with the results obtained after the oxidation test. The TBC systems with two different top coating material were subjected to isothermal oxidation tests at 900 °C, 1000 °C and 1100 °C for 8, 24, 50 hour periods, respectively. After the oxidation tests, XRD, SEM, EDX-elemental analyses as well as the changes in the thickness of Thermal Growth Oxide Layer (TGO) were investigated in detail. The obtained data were compared before and after the tests, and the findings were evaluated and recorded in light of other related studies within the literature.