Ceramic thermal barriers for demanding turbine applications

Ceramic thermal barrier coatings (TBCs) offer the potential to significantl y improve efficiencies of aero engines as well as stationary gas turbines f or power generation. On internally cooled turbine parts temperature gradien ts of the order of 100 to 150 K can be achieved, however, state-of-the-art TBCs, typically consisting of an yttria-stabilized zirconia top coat and a metallic bond coat deposited onto a superalloy substrate, are mainly used f or lifetime improvements. Further efficiency improvements require TBCs bein g an integral part of the component which, in turn, requires reliable and p redictable TBC performance. Presently, TBCs fabricated by electron beam phy sical vapor deposition are favoured for high performance applications. In t he present paper critical R&D needs for such TBC applications are highlight ed. A reduced thermal conductivity is the key driver for development of adv anced microstructures of the ceramic top layer. E.g., multilayer TBCs provi de lower thermal conductivities than standard systems. Increased temperatur e capability of the ceramic is necessary to extent surface temperature limi tations. Lifetime prediction modeling is becoming increasingly important si nce predictable component performance is strictly required. An improved und erstanding of the deposition process is essential for lifetime optimization of the TBC. Finally, improvement of bond coat oxidation and hot corrosion resistance is crucial for reliable TBC operation under more demanding opera ting conditions.