Thermal diffusivity/microstructure relationship in Y-PSZ thermal barrier coatings
A set of yttria partially stabilized zirconia coatings with different thickness was deposited on flat nickel-base alloy coupons by air plasma spray (APS) under uncontrolled temperature conditions. In this way, the length of the spraying process (and consequently the coating thickness) had a direct effect on phase composition as well as on the thermal properties of the material. In particular, both the monoclinic phase percentage and thermal diffusivity increased considerably with the thickness. Because this trend was observed together with a slight but clearly visible increase in the total porosity, the interpretation of the results was not straightforward, but required a detailed discussion of the thermal transport mechanism. Considering the complex microstructure typical of APS coatings and the relevant role of porosity, it was shown how a modest reduction in the fraction of closed pores can account for the observed increase in diffusivity. It was then proposed that the volume change associated with the progressive tetragonal to monoclinic phase transformation can be responsible for the reduction of the closed porosity of lenticular shape oriented parallel to the surface, in spite of the observed increase in the total porosity.
Keywordsair plasma spray photothermal radiometry thermal barrier coatings thermal diffusivity XRD Y-PSZ
Unable to display preview. Download preview PDF.
- 1.V.P. Swaminathan and N.S. Cheruvu, Gas Turbine Hot-Section Materials and Coatings in Electric Utility Applications, Advanced Materials and Coatings for Combustion Turbines, V.P. Swaminathan and N.S. Cheruvu, Ed., ASM International, 1994Google Scholar
- 2.Proc. Quadriennial International Conf. Power Stations, 13–15 Oct 1997, Association Ingenieurs de Montflory, 1997Google Scholar
- 3.M.G. Hocking, V. Vasantaree, and P.S. Sidky, Metallic & Ceramic Coatings: Production, High Temperature Properties & Applications, Longman Scientific & Technical, Harlow, Essex, UK, 1989Google Scholar
- 6.D.P. Almond and P.M. Patel, Photothermal Science and Techniques, Chapman & Hall, London, 1996Google Scholar
- 7.L. Fabbri, F. Cernuschi, P. Fenici, S. Ghia, and G.M. Piana, Photothermal Techniques for Nondestructive Characterisation of Turbine Blade Coatings, Materials for Advanced Power Engineering, Part II, D. Coutsouradis et al., Ed., Kluwer Academic, Dordrecht, The Netherlands, 1994, p 1377–1381Google Scholar
- 8.G. Busse and H.G. Walther, Photothermal Nondestructive Evaluation of Materials with Thermal Waves, Progress in Photothermal and Photoacoustic Science and Technology, Vol 1, Principles and Perspectives of Photothermal and Photoacoustic Phenomena, A. Mandelis, Ed., Elsevier Science, 1992, p 218–222Google Scholar
- 9.Technical bulletin No. 10.311, Metco Inc., Westbury, NY 1985Google Scholar
- 12.B. Shultz, Thermal Conductivity of Porous and Highly Porous Materials, High Temp.-High Press., Vol 13, 1981, p 649–660Google Scholar