Atmospheric plasma sprayed thick thermal barrier coatings with high segmentation crack density.pdf

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Atmospheric plasma sprayed thick thermal barrier coatings with high segmentation crack density.pdf

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Atmospheric plasma sprayed thick thermal barrier coatings with high segmentation crack density

/locate/surfcoat Surface Coatings Technology 186 (2004) 353–363Atmospheric plasma sprayed thick thermal barrier coatings with high segmentation crack density H.B. Guo*, R. Va?en, D. Sto?ver Institut fu?r Werkstoffe und Verfahren der Energietechnik 1, Forschungstentrum Ju?lich GmbH, 52425 Ju?lich, GermanyReceived 15 July 2003; accepted in revised form 8 January 2004 Available onlineAbstract Atmospheric plasma sprayed thick thermal barrier coatings (TBCs), comprising of 1.5 mm thickness yttria stabilized zirconia (YSZ) coating, have been developed for increasing thermal protection of combustor applications. Different segmentation crack densities of the YSZ coating were created by controlling the deposition conditions. It was found that the substrate temperature played a dominant role in determining the segmentation crack density. The density was found to increase with the increase of substrate temperature and liquid splat temperature. High passage thickness, if achieved by low plasma gun speed, contributed to improve the segmentation crack density. The density could not be effectively improved by increasing the powder feed rate, although a high passage thickness was obtained in this case. The pores, mainly consisting of delaminations with the radii range between 0.02 and 1 Am, prevent the segmentation cracks from propagation. The coatings sprayed at high substrate temperature show an excellent intersplat bonding and often even continuous columnar grains through several splats. Additionally, horizontally branching cracks were also formed together with the segmentation cracks when a high lamellar thickness was used during the spraying. Thermal cycling tests showed that the coating with a segmentation crack density of approximately 3.6 mm1 had a lifetime of more than 1700 cycles at 1238 jC (surface)/938 jC (bond coat), indicative of excellent thermal shock resistance. Failure of the TBCs occurred by chipping in the surface layer of YSZ coating, which is different from