Papers by Author: Justine Fenech

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Authors: Lisa Pin, Florence Ansart, Justine Fenech, Philippe Lours, Jean Pierre Bonino, Julien Sniezewski, Yannick Le Maoult
Abstract: This paper deals with the development of a new synthesis technique for functional materials such as Yttria Stabilized Zirconia (YSZ) in the field of thermal barrier coatings. Currently, Thermal Barrier Coatings (TBCs) are manufactured by dry route technologies (EB-PVD or plasma spray) but such methods are directional and often require costly investments and complex operations. For these applications, the sol-gel route, a non directional method, is developed, to process, by suitable chemical modifications, nanocrystalline materials with a controlled morphology. The main advantage of this method is to decrease the crystallization temperature, much lower than the conventional processes, allowing the synthesis of reactive substituted zirconia powders with nanometric particles size. In this study, several suitable architectures for thermal barrier coatings have been achieved in order to show that this process is appropriate for repairing damaged TBC compared to conventional processes. The next step is to investigate spallation mechanisms and overall TBC durability by cyclic oxidation. Preliminary results are promising and research will be develop further to optimize both processing and cyclic oxidation behavior.
Authors: Justine Fenech, Céline Viazzi, Florence Ansart, Jean Pierre Bonino
Abstract: Thermal Barrier Coatings (TBCs) are used as insulators on hot section components to reduce operating temperatures in aircraft engines and industrial gas turbine. The TBC system consists of two layers: the ceramic top coat traditionally Yttria Stabilized Zirconia (YSZ) with a low conductivity, and the bond coat generally MCrAlY, M=Ni and/or Cr or Co or Pd or Pt modified aluminides. In the industry, two dry-route processes used to deposit TBCs give quite different microstructures of coatings. In one hand, coatings resulted by plasma spraying (PS) present a lamellar microstruture with a low thermal conductivity in the range from 0.7 to 0.9 Wm−1K−1. In the other hand, Electron Beam Physical Vapour Deposition (EBPVD) coatings with columnar microstruture coatings present the best mechanical performances but perpendicular orientation of the columns makes their thermal conductivity twice higher compared to PS coatings. The present study proposes the elaboration of zirconia coatings via the sol-gel route combined with dip-coating process. It is a versatile process able to produce either thin ceramic coatings or thick deposits. The main advantage of this method is to decrease the crystallization temperature, much lower than conventional processes. Moreover, the sol-gel process is a nondirectional deposition technique, which is very different to the physical methods described above. Doped zirconia have been chosen to constitute isolating multilayers coatings. Sol formulation, slurries stability but also dip-coating conditions have been optimized in order to obtain homogeneous layers on nickel based superalloys substrates.
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