Performance and Degradation Mechanisms of Thermal Barrier Coatings for Turbine Blades: a Review of Onera Activities


M.-P. Bacos, J.-M. Dorvaux, O. Lavigne, R. Mévrel, M. Poulain, C. Rio,
M.-H. Vidal-Sétif

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.

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