Les systèmes barrières thermiques pour aubes de turbine

Les systèmes barrières thermiques pour aubes de turbine sont des systèmes multicouches dont la structure et la composition évoluent à haute température. Cette évolution, qui est liée à l'interaction avec l'environnement oxydant, entraîne des modifications des champs de contraintes présents dans ces systèmes et qui peuvent provoquer leur endommagement, voire leur ruine. Ce texte synthétique présente succinctement les systèmes actuellement utilisés et la problématique de l'interaction entre aspects mécaniques et environnement dans la turbine

Microindentation instrumentée de 20 à 900 °C sur matériaux constitutifs de barrières thermiques

Nous décrivons le principe et les possibilités d’appareils de microindentation instrumentée conçus pour fonctionner jusqu’à 1000 °C et 1200 °C. Des exemples de résultats (microdureté, comportement en fluage) sont donnés sur des alliages de type NiAl(Pt), qui sont des matériaux de base pour constituer la couche de liaison de barrières thermiques pour aubes de turbines. La technique de microindentation instrumentée à chaud ouvre la voie à la détermination de lois de comportement mécanique local de revêtements et de phases individuelles dans un matériau multiphasé

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

International audienceThermal 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 an 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 well as interfacial toughness. These evolutions, combined with applied external stresses may lead to bond coat rumpling, crack formation at the bond coat/ceramic interface and eventually the ceramic layer may spall off. In addition to these intrinsic degradation modes, interactions with environment can accelerate the system degradation. The present paper reviews the ageing phenomena occurring in thermal barrier coatings at high temperature and describe their degradation mechanisms, with illustrations taken from service experience and laboratory tests

10 Years-Activities at ONERA on Advanced Thermal Barrier Coatings

International audienceDeveloping 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

Diffusion of sputtered inconel 617 coatings in titanium

INCONEL 617 coatings 10-to 13-μm thick were radio frequency (RF) magnetron sputtered onto commercially pureα-titanium substrates and heat-treated at 800 °C for 2 hours. The resulting structures were examined in cross section by scanning electron microscopy (SEM) and analytical transmission electron microscopy (TEM). Scanning electron microscopy of polished and etched cross sections showed that the coating remained continuous, and as a result of inter-diffusion, a layer 66-μn thick had formed below the coating. Examination of the coating near the free surface by TEM showed it contained both M23C6 and M6C carbide precipitates, while several micron-thick layers containing intermetallic phases such as σ, γ′, and Ti2Ni were found near the substrate. Kirkendall voids 75 to 300 Å in diameter were present near the original INCONEL 617/α-titanium interface. The microstructure further below that interface contained a thin layer of titanium martensite and Widmanstätten α + Ti2Ni. No TiNi or TiNi3 was found. The diffusivity of nickel and titanium was reduced several orders of magnitude and is attributed primarily to the formation of intermetallic compounds in the coating and substrate. © 1990 The Metallurgical of Society of AIME