Evaluation of oxidation and thermal cyclic behavior of YSZ, Gd2Zr2O7 and YSZ/Gd2Zr2O7 TBCs

Abstract

Thermal barrier coatings (TBCs) are widely used to increase gas turbine efficiency and to prolong the lifetimes of superalloy substrates. Yttria (7-8%) stabilized zirconia (YSZ) is used as a state of the art TBC top coating material. In recent years, rare earth zirconates have drawn interest as top coating materials due to their high phase transformation temperature and low thermal conductivity. In the present research, CoNiCrAlY powders were sprayed on Inconel 718 superalloy substrates using high velocity oxy fuel (HVOF) deposition technique. YSZ, Gd2Zr2O7 (GZ) and YSZ/GZ top coats were then deposited on the resulting bond coat using EB-PVD technique. The produced TBCs were exposed to isothermal oxidation at 1100 degrees C for 4 different periods, and furnace thermal cyclic tests were conducted at 1150 degrees C. After thermal loadings, TGO (thermally grown oxide) growth behavior and crack surfaces of TBCs were evaluated. Samples were compared with each other using analysis techniques like scanning electron microscopy (SEM), energy dispersive sprectrum (EDS) elemental mapping and X-ray diffraction (XRD) before and after the oxidation tests. The results showed that double layered TBC system is more durable against high temperature degradations.