double layer for improved thermal and optical properties Federico Cernuschi*, H. Kaßner**, A. Stuke**, R.Vaßen**, D. Stöver** Second International Workshop on Suspension and Solution Thermal Spraying (S2TS) 2008 Tours, 5-7 Giugno 2008 PRESENTAZIONE POWER POINT * CESI RICERCA ** FORSCHUNGSZENTRUM JÜLICH, INSTITUT FOR ENERGY RESEARCH, GERMANY In nowadays state of the art gas turbines thermal barrier coatings (TBCs) are utilized in the high-pressure turbine section for lifetime improvement, increased turbine efficiency and performance. Despite the widespread application still further developments are necessary due to economical and ecological aspects. Especially the operation regime of gas turbines and their heat loss have to be optimized. Higher inlet temperatures and improved compression ratios result not only in a higher conductive heat transfer, also the fraction of near infrared radiation emitted by turbine walls and combustion gases increases significantly. The thermal conductivity as well as the optical properties, which determine the radiation heat transfer, depend directly on the used TBC materials and the microstructure of the coatings. The widely-used material for TBCs in gas turbines, yttria partially stabilized zirconia (YSZ), is as most oxide ceramics semi-transparent in the relevant wavelength range and hence, shows poor shielding of the thermal radiation. Here the suspension plasma spraying (SPS) process offers new possibilities by adjusting new or improved microstructure features. These modifications lead to an enhanced backscattering of radiation and decreased thermal conductivity of the coatings. To evaluate the influence of the different microstructural features on the optical and thermal properties single APS and SPS layer were investigated. The results show that the processing of YSZ by SPS improves both thermal and optical properties considerably. In the paper especially a combination of APS and SPS coatings is discussed. Such a combination in terms of a double layered system seems to be a good alternative to combine the advantages of both processes. For the optimization of the APS and SPS double layer coatings, different coating structures and thickness values were tested. The results show, that such a YSZ double layer system processed by both APS and SPS offers attractive coating properties.