TGO growth and kinetic study of single and double layered TBC systems

Thermal barrier coating (TBC) systems are widely used to prolong the lifetime of hot section components in gas turbines. Oxidation degradation at high temperature is inevitable despite the use of TBC systems. In the current study, Yttria stabilized zirconia (YSZ)/CoNiCrAlY/Inconel 718 and La2Zr2O7 (LZO)/YSZ/CoNiCrAlY/Inconel 718 TBC systems were produced and exposed to high temperature oxidation tests. After the tests, a thermally grown oxide (TGO) layer formed at the interface between the bond and top coating due to the oxidation of bond coating. This layer has a critical importance for the lifetime of TBCs. The oxidation kinetics, rate constants, and activation energy values of both TBC systems were calculated using TGO thickness values. At the end of the oxidation tests, the double-layered LZO/YSZ TBC system exhibited better performance thanks to the lower oxygen permeability of LZO considering oxidation kinetics results and microstructural investigations. However, the formed TGO layer consisting of alumina and mixed oxides (MOs) led to crack formation at the interface. Besides, higher temperatures and increasing oxidation periods also degraded the integrity of top coatings due to the sintering effect. Chemical incompatibility did not affect the interface durability of the LZO/YSZ TBC system during the oxidation tests.