Development of thermal barrier coating systems from Al microparticles. Part I: Influence of processing conditions on the mechanisms of formation

International audienc

Thermal Transport Properties of New Coatings on Steels for Supercritical Steam Power Plants

International audienc

Thermo-Physical Properties of HR3C and P92 Steels at High-Temperature

Austenitic HR3C and ferritic-martensitic P92 steels are the materials of interest from a mechanical standpoint for the manufacturing of thermal exchangers of the next generation of steam power plants. In order to evaluate their capacity to transfer heat, thermal conductivity calculations have been conducted through the measurements of thermal diffusivity, specific heat capacity and density. It will be shown that the heat capacity, density, thermal expansion coefficient and thermal diffusivity evolve continuously with temperature in the HR3C material but not in the P92 steel. The heterogeneous thermal behaviour appears to be associated with its ferromagnetic transition rather than to the microstructural evolution. Nevertheless, the results for both steels did not exhibit significant differences between thermal conductivities at the intended temperature of service

Thermal insulation of YSZ and erbia-doped yttria-stabilised zirconia EB-PVD thermal barrier coating systems after CMAS attack

The impact of small deposits of calcium–magnesium–aluminium silicates (CMAS) on the top of thermal barrier coatings (TBCs) made of yttria-stabilised zirconia (YSZ) produced via electron-beam physical vapour deposition (EB-PVD) is shown to play a role in the microstructural and chemical stability of the coatings; hence, it also affects the thermal insulation potential of TBCs. Therefore, the present work investigates the degradation potential of minor CMAS deposits (from 0.25 to 5 mg·cm−2) annealed at 1250 °C for 1 h on a novel Er2O3-Y2O3 co-stabilised ZrO2 (ErYSZ) EB-PVD TBC, which is compared to the standard YSZ coating. Due to the higher reactivity of ErYSZ coatings with CMAS, its penetration is limited in comparison with the standard YSZ coatings, hence resulting in a better thermal insulation of the former after ageing

Facteurs influençant la capacité d'isolation thermique de différents systèmes de revêtements "barrière thermique"

In aeronautical gas turbine engines, the metallic materials employed in the hottest sections are subject to very harsh chemical environments at high pressures and temperatures. Therefore, thermal barrier coating systems (TBCs) are applied onto nickel-based superalloy substrates. These multi-layered systems (ceramic yttria-stabilized zirconia (YSZ) / MCrAl or NiPtAl bond coats / cooled substrate) lower the temperature at the components surface, which ensures an adequate thermomechanical behaviour and reduces the oxidation/corrosion rates. However, the increase of the turbine inlet temperature (increased engine performance) brings about new degradation phenomena (e.g. CMAS) and loss of efficiency of the current TBCs. Therefore, understanding the evolution of the insulation ability of TBCs in such harsh environments is key from both the scientific and technological perspectives to estimate the lifetime of these coatings, hence that of the engines. Based on current plasma-sprayed (PS) and electron-beam physical vapour deposited (EB-PVD) YSZ coatings, this thesis seeks to provide a better comprehension on the relationships between the intrinsic properties of the current TBCs and their thermal insulation capacity as a basis for the development of future coatings. Also, this work studies an alternative solution to create a TBC made of hollow alumina microspheres by the slurry route. We will show that the sintering of the YSZ, the evolution of crystal phases, the reactions between YSZ and CMAS and the growth of thermal oxides alter the thermal diffusivity to different extents. In contrast, the evolution of the thermal diffusivity with temperature is less marked with the slurry alumina coatings, which appear more stable when hybrid Ar/air annealing atmospheres are employed upon their synthesis.Dans les turbines à gaz aéronautiques, les matériaux employés dans les parties les plus chaudes sont soumis à des environnements chimiques extrêmes, sous fortes pressions et températures. Ainsi, des systèmes de revêtement « barrière thermique, BT » sont appliqués sur les substrats en superalliage à base nickel. Ces systèmes multicouches (zircone stabilisée à l’yttrine (YSZ) /couche de liaison en MCrAl ou NiPtAl/substrat refroidi) permettent d’abaisser la température à la surface des pièces, conduisant à un comportement thermomécanique adéquat et à une diminution des vitesses d’oxydation/corrosion. Cependant, l’augmentation nécessaire de la température des gaz d’entrée de turbine (augmentation du rendement moteur) entraîne de nouveaux phénomènes de dégradation (CMAS) et une perte d’efficacité des revêtements BT actuels. Par ailleurs, l’évaluation de la durée de vie des revêtements BT s’avère cruciale pour déterminer celle des moteurs. Comprendre l’évolution du pouvoir isolant des revêtements BT en environnement agressif constitue donc un enjeu essentiel du point de vue scientifique et technologique. A partir des revêtements couramment employés (YSZ) déposés par projection plasma (PS) ou en phase vapeur (EB-PVD), la présente étude a visé à mieux comprendre l’effet de l’évolution des propriétés microstructurales et chimiques des revêtements sur leur pouvoir isolant, dans le but de développer des outils nécessaires à la mise au point des revêtements du futur. De plus, une partie des travaux menés a porté sur une solution alternative plus économique et écologique d’élaboration de revêtements BT, fondée sur un procédé par voie barbotine, permettant in fine d’obtenir une barrière constituée de microsphères creuses d’alumine. Ce travail a permis de montrer que l’évolution par frittage des phases céramiques en YSZ, les changements de phase cristalline, les réactions avec les CMAS et la croissance d’oxydes thermiques modifient la diffusivité thermique. En revanche, celle-ci évolue moins avec la température puisque les revêtements en alumine issus de barbotines se sont avérés plus stables et ce, notamment, lorsque leur élaboration a été réalisée sous atmosphères hybrides (mélanges Ar/air)

Development of Thermal Barrier Coating Systems from Al Microparticles—Part II: Characterisation of Mechanical and Thermal Transport Properties

In this study, the mechanical resistance and the thermal insulation potential of novel thermal barrier coatings (TBCs) made of a foam of hollow alumina particles are assessed through scratch testing, micro-indentation and thermal diffusivity measurements using laser-flash. The thermal diffusivity of the foam coatings ranges between 0.6 × 10−7 and 5 × 10−7 m2·s−1 and is thus comparable with the thermal insulation potential of the standard plasma-sprayed (PS) and electron beam–physical vapour-deposited (EB-PVD) TBCs made of yttria-stabilised zirconia (YSZ). The coatings annealed in more oxidative atmospheres exhibit greater mechanical resistance due to the thickening of the alumina shells and the increased sintering of the foam. However, when the oxidation is poorly tailored, the adhesion of the foam to the substrate decreases due to the presence of unwanted oxide that grows at the substrate/coating interface

High Temperature Oxidation of Enamel Coated Low-Alloyed Steel 16Mo3 in Water Vapor

New types of ceramic coatings based on SiO2-Na2O-B2O3-TiO2 oxide phases were investigated as protection for boiler steel in power generation systems. Low-alloyed Cr-Mo 16Mo3 steel was coated with different compositions of enamel coatings to assess the protective potential of these coatings under water vapor at high temperatures. Oxidation at 650 °C for 50 h in Ar + water vapor was performed in a TGA apparatus to investigate the oxidation kinetics. The results indicate that the ceramic coatings provided a high degree of protection for the steel exposed to such conditions compared to the uncoated 16Mo3 steel. Furthermore, despite the formation of cracks in the coatings, no spallation from the steel surface was observed. Interconnected porosity in the coatings is suspected to provoke interfacial degradation

High Temperature Oxidation of Enamel Coated Low-Alloyed Steel 16Mo3 in Water Vapor

New types of ceramic coatings based on SiO2-Na2O-B2O3-TiO2 oxide phases were investigated as protection for boiler steel in power generation systems. Low-alloyed Cr-Mo 16Mo3 steel was coated with different compositions of enamel coatings to assess the protective potential of these coatings under water vapor at high temperatures. Oxidation at 650 °C for 50 h in Ar + water vapor was performed in a TGA apparatus to investigate the oxidation kinetics. The results indicate that the ceramic coatings provided a high degree of protection for the steel exposed to such conditions compared to the uncoated 16Mo3 steel. Furthermore, despite the formation of cracks in the coatings, no spallation from the steel surface was observed. Interconnected porosity in the coatings is suspected to provoke interfacial degradation

Développement et comportement mécanique et en tribologie de revêtements durs pour application en réacteur nucléaire Na

National audienc

Evaluation of the Compatibility of Aluminide Coatings in High-Temperature Sodium for Fast Reactor Application

International audienceNickel and iron aluminide coatings were identified as possible candidates for hardfacing materials in Sodium Fast Reactors. Both coatings were developed on two steel grades of interest for the next French Sodium Fast Reactor prototype, 316L(N) and T91. Pack cementation and slurry were employed as aluminization processes. The compatibility of all coatings with purified Na was evaluated at 550 A degrees C for exposure times up to 4250 h. All coatings evidenced high chemical stability in Na even though Na penetration and slow coating dissolution could be evidenced. The penetration depth of Na was observed to depend on the coating nature induced by the deposition process