Microstructural evolution of GdZ and DySZ based EB-PVD TBC systems after thermal cycling at high temperature

Lower thermal conductivity and high temperature stability are the two properties which are highly desired from ceramic top coat materials in TBC systems. Gadolinium Zirconate, Gd2Zr2O7, (GdZ) and Dyprosia Stabilized Zirconia (DySZ) are two of the candidate materials with such properties and consequently the TBC system would be able to work at higher turbine inlet temperature (TIT) or the lifetime can be increased. In the present study, life time measurements are done for single and double layered Electron Beam Physical Vapor Deposition (EB-PVD) GdZ and DySZ samples by thermal-cycling tests. The double layered TBCs consisted of a thin 7YSZ layer and, on top, the new candidate material. Both single and double layered samples of GdZ and DySZ have shown similar or better lifetimes than the standard 7YSZ samples. However, single layered TBCs showed better lifetime results than the respective double layers. In this study, changes in the microstructure, diffusion of elements and sintering of the TBC materials with aging are observed.