EB-PVD Thermal Barrier Coatings Research Articles

EB-PVD Thermal Barrier Coatings for Aeroengines and Gas Turbines

EB-PVD Thermal Barrier Coatings for Aeroengines and Gas Turbines

Oxidation and damage of EB-PVD thermal barrier coatings under thermal cycling

Oxidation and damage of EB-PVD thermal barrier coatings under thermal cycling

R&D Status and Needs for Improved EB-PVD Thermal Barrier Coating Performance

ABSTRACTThe key issues for thermal barrier coating development are high temperature capability and durability under thermal cyclic conditions as experienced in the hot section of gas turbines. Due to the complexity of the system and the interaction of the constituents, performance improvements require a systems approach. However, there are issues closely related to the ceramic top coating and the bond coat, respectively. Reduced thermal conductivity, sintering, and stresses within the ceramic coating are addressed in the paper as well as factors affecting failure of the TBC by spallation. The latter is primarily governed by the formation and growth of the thermally grown oxide scale and therefore related to the bond coat. A strategy for lifetime assessment of TBCs is discussed.

Influence of the surface roughness on the oxide scale formation on MCrAlY coatings studied in situ by high temperature X-ray diffraction

In modern stationary gas turbines for electric power generation the life time of the blades is mainly controlled by the oxidation resistance of the coatings. In the case of protective overlay coatings the surfaces are generally shot peened, whereas bond coats for EBPVD thermal barrier coatings need a smooth surface. For a better understanding of the influence of the surface roughness on the oxide scale formation, in situ studies using high temperature X-ray diffraction were performed on an MCrAlYRe coating with 12% Al and 3% Re for the use as overlay and as bond coat. The measurements were performed in air at 950 and 1000°C. The results show differences in the oxide scale formation on the same coating with an as-sprayed and a polished surface. On the as-sprayed surface Cr 2 O 3 and spinels were observed besides α-Al 2 O 3 in the initial state whereas on the polished surface a coherent α-Al 2 O 3 scale with inclusions of YAlO 3 was observed from the beginning.

Oxide scale growth on MCrAlY coatings after pulsed electron beam treatment

Abstract A new electron beam treatment method was applied to the surface of LPPS–MCrAlY coatings to improve the oxide scale behavior. The electron beam generated by the newly developed facility GESA has a diameter of about 10 cm and sufficient power density to melt a surface layer of about 20 μm of this area by just one electron beam pulse. Cooling rates are around 10 6 K/s and result in a nanometer grained single phase structure of the surface layer, that solidifies directionally. The high roughness of the as sprayed surface is reduced by the GESA process from R A =5 to 1.5 μm. The oxidation behavior of treated coatings at 950°C in air was examined. During oxidation a single phase α-alumina scale developed on the treated surface with a considerably lower growth rate as compared to the untreated coatings. Therefore, it is expected that electron beam treatment improves the oxidation resistance of MCrAlY coatings and their suitability as a bond coat for EBPVD thermal barrier coatings.

Thermocyclic Behaviour of Microstructurally Modified EB-PVD Thermal Barrier Coatings

On a examine l'effet des parametres divers du procede EB-PVD sur la microstructure colonnaire des barrieres thermiques en zircone, partiellement stabilisee. Le diametre des colonnes, le degre d'ordre de leur formation et la densite specifique (g/cm 3 ) de la couche de zircone sont en rapport etroit avec ces parametres. Les observations microstructurales ont cree un nouveau modele en ce qui concerne la formation des zones de structure. On a applique des revetements en zircone YPSZ de deux structures differentes sur des echantillons de superalliage IN 100 sur lesquels on avait deja applique une sous-couche de type NiCoCrAlY. Deux types de barrieres thermiques, dont les colonnes sont de deux diametres differents ont ete soumis a un cyclage thermique entre 1100°C et 130°C dans un four et a un cyclage entre 900°C et 25°C dans la flamme d'un bruleur Mach 0,3. Les resultats montrent une correlation entre la geometrie des colonnes des barrieres thermiques et leur duree de vie. Les resultats sont a discuter en rapport avec la microstructure des revetements.

Microstructure and phase stability of EB-PVD alumina and alumina/zirconia for thermal barrier coating applications

This paper describes recent progress on research aimed at improving the performance of EB-PVD thermal barrier coatings (TBCs) for gas turbine applications by incorporating alumina as an oxygen diffusion barrier between the bond coat and zirconia. Two approaches are being investigated, either a single, discrete alumina layer, or a graded alumina/zirconia layer. This paper reports on preliminary experiments in which alumina was evaporated under different conditions, and the phase content and morphology of the coatings were characterized. Deposition rate and chamber pressure had a significant effect on the microstructure of the coatings; however, phase formation was essentially unaffected. In agreement with previously published results, α-Al 2O 3 was produced either by in situ deposition on substrates heated to temperatures near 1000 °C, or by heat treatment of metastable as-deposited alumina coatings at temperatures above 1100 °C. By continuously changing the vaporization ratio of alumina and zirconia as a function of deposition time, TBCs exhibiting composition gradients through the film thickness were produced. In related work, suitable source materials for alumina deposition were produced using a new sinterless powder processing route involving bimodal powder mixtures.