Substrate Effect on the Lifetime of EB-PVD TBC Systems With 7YSZ and GDZ as Ceramic Top Coat Materials

Abstract

Thermal barrier coatings (TBCs) consist of a multi-layered system where the different layers are deposited to improve the high temperature capability of the underlying substrate material. Substrate materials are usually made of Ni-based superalloys which have an outstanding combination of high-temperature strength, toughness and resistance to degradation in corrosive or oxidizing environments. In this study, the effect of different substrate materials on cyclic TBC lifetime has been studied by using two different superalloys, IN100 and CMSX-4, as the substrate materials. Two different ceramic topcoat materials, 7wt. % yttria partially stabilized zirconia (7YSZ) and Gadolinium Zirconate (GdZ), have been deposited on NiCoCrAlY bond coats. All depositions in this study have been carried out by Electron Beam Physical Vapor Deposition (EB-PVD). Lifetime measurements have been done by holding the systems at 1100°C for 50mins and then reducing the temperature to ambient level by forced air cooling for 10mins. The TBC lifetime in case of IN100 substrates is higher than on CMSX-4. The use of GdZ as topcoat material improves the lifetime for both IN100 and CMSX-4 based TBC systems, however, the lifetime for CMSX-4 based TBC system is still shorter than its IN100 counterpart. In this study, lifetime comparisons, changes in the microstructure and diffusion of different elements in the system are investigated.