59. Further Improvement of the Properties of Sprayed TBC Using Hollow PSZ Spheres
- Edgar Lara-Curzio and
- Michael J. Readey
Published Online: 26 MAR 2008
Copyright © 2004 The American Ceramics Society
28th International Conference on Advanced Ceramics and Composites B: Ceramic Engineering and Science Proceedings, Volume 25, Issue 4
How to Cite
Bertrand, G., Roy, P., Mévrel, R., Meunier, C. and Demange, D. (2008) Further Improvement of the Properties of Sprayed TBC Using Hollow PSZ Spheres, in 28th International Conference on Advanced Ceramics and Composites B: Ceramic Engineering and Science Proceedings, Volume 25, Issue 4 (eds E. Lara-Curzio and M. J. Readey), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9780470291191.ch59
- Published Online: 26 MAR 2008
- Published Print: 1 JAN 2004
Print ISBN: 9780470051528
Online ISBN: 9780470291191
- chemical etching;
- scanning electron microscopy;
- silicon carbide;
- carbide derived carbon;
- monocrystalline sic wafers
The life and thermal properties of plasma sprayed TBCs - widely used in gas turbine engines - are closely related to the microstructure of the ceramic top coating, which can be described as a build-up of flattened lenticular grains. The thermal conductivity of this ceramic coating is highly dependent on the void shapes and networks which are in turn determined by both the spraying conditions and the feedstock material.
The first step in improving the thermal behaviour of plasma-sprayed TBC coatings is to control and optimise the powder feedstock. In this work, ceramic powders have been processed by spray drying, which is a most versatile method by which an aqueous suspension (slurry) is transformed into a dry agglomerated powder by spraying the fluid feed material into a stream of heated air. It was shown that the formulation and the state of dispersion of the slurry allow to control the powder morphology (from dense to hollow spheres). Moreover, in the case of hollow powder, the thickness of the shell could be varied from 0.1 to 0.3 of the granule diameter. According to these results, a new hollow powder (size ranging from 36 to 130 μm with a 10μm shell thickness) was elaborated by spray drying as an original feedstock to produce plasma sprayed TBC. The agglomerated powder was strengthened in an oven and then compared to a commercial hollow PSZ powder.
Seven spraying parameters concerning the plasma (primary and secondary gas flow rates, are current), the cooling rate and the process cinematic (spraying distance, spraying angle, linear speed) were selected. A two level Taguchi fractional-factorial L16 design was applied to study the influence of process parameters on the quality of the coatings in terms of deposition efficiency, roughness (Ra), porosity (image analysis technique and Archimedean method) and microstructure (XRD). According to this analysis, coatings were selected from the DOE, heat treated (100h-1100°C, 100h-1200°C, 100h-1300°C) and characterized with respect to porosity and crystalline structure. Finally, the thermal diffusivity of these coatings, which exhibited different morphologies, has been measured by the laser flash method. Results clearly show that a profit regarding the thermal insulation capability of the plasma sprayed PSZ TBC can be expected from the powder design.