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International audience; Developing thermal barrier coatings operating at higher temperature and/or for very long durations (commercial aircraft applications) is one of the technological and economical challenges for engine manufacturers. This includes the search for (i) low thermal conductivity, high thermal stability and CMAS resistant ceramic top coat, and (ii) alternative low cost bond coat with improved oxidation resistance and chemical compatibility with the substrate. This paper reviews the rationale sustaining the choice of new materials for each layer and presents some recommendations to develop more robust and more efficient systems with increased lifetime.

Thermal barrier coatings are used to protect blades and vanes in the hot sections of gas turbines. They consist of a thick porous ceramic layer deposited on a alumina forming metallic bond coat in contact with the nickel- based superalloy substrate. They are designed to prolong the components lifetimes or to increase gas temperature, and therefore efficiency. In service, the structure and composition of the various layers evolve, due to sintering of the ceramic layer, oxidation of the bond coat, and interdiffusion phenomena with the substrate. As a result, the properties of each layer are affected, as is the interfacial toughness. These evolutions, combined with applied external stresses, may lead to bond coat rumpling, crack formation at the bond coat/ceramic interface and the ceramic layer may eventually spall off. In addition to these intrinsic degradation modes, interactions with the environment can accelerate the system degradation. This paper reviews the aging phenomena occurring in thermal barrier coatings at high temperatures and describes their degradation mechanisms, with illustrations from service experience and laboratory tests., Journal Aerospace Lab, Issue 3, November 2011; ISSN: 2107-6596