Papers by Author: Florence Ansart

Abstract: Due to the environment and economical questions, the use of cadmium coatings, in the aeronautical and automotive industries, has been prohibited. In this context, ZnNi coating alloys have been propose to replace cadmium coatings due to its properties. However, in order to postpone the corrosion of ZnNi alloy, hybrids films obtained by sol-gel process have been studied. In this work, hybrids films were obtained on ZnNi coating by dip-coating process from a sol constituted of alkoxide precursors: γ-methacryloxypropyl-trimethoxysilane and tetraethoxysilane with cerium nitrate addition (0.01 M). Two withdrawal speeds of substrates from the sol were applied: 5 cm.min^-1 and 10 cm.min^-1 .The films obtained were evaluated by morphological (SEM and AFM) and electrochemical characterization. The superior corrosion protection performance was observed for the ZnNi/hybrid film system obtained with withdrawal speed of 10 cm.min^-1, thought, the presence of discontinuities were observed in this film.

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.

Abstract: This paper examines the erosion and cyclic oxidation performance of novel thermal barrier coatings produced via the sol-gel route. The ceramic top coat, with a thickness of 5-80 m, was deposited via a sol-gel route onto standard MCrAlY and PtAl bond coats. In both the erosion and the cyclic oxidation tests it was found that the bond coat had a profound affect on the results. The erosion of the sol-gel coatings were compared to standard EB PVD and PS TBCs and were found to be significantly higher. The effect of aging (100 h at 1100°C) on the erosion rates was also evaluated and was found to increase the erosion rates. The information obtained from the erosion and cyclic oxidation tests have highlighted the need to develop and optimise the parameters for producing thicker coatings