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3778 |
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Thursday, May 22, 2014, Hall H2 12:20 PM Power Generation - Industrial Gas Turbines 2 |
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Intermediate PVD layer as diffusion barrier in turbine coating concept |
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Ibrahim Ali / Institute of Materials Science and Engineering, Germany Daniel Wett / Institute of Materials Science and Engineering, TU-Chemnitz, Germany Thomas Grund*/ Institute of Materials Science and Engineering, TU-Chemnitz, Germany Thomas Lampke/ Institute of Materials Science and Engineering, TU-Chemnitz, Germany Daisy Nestler/ Institute of Materials Science and Engineering, TU-Chemnitz, Germany Bernhard Wielage/ Institute of Materials Science and Engineering, TU-Chemnitz, Germany |
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Standard thermal barrier coating systems consist of yttria-stabilized zirconia (YSZ) top coat on so called M-CrAlY bond coat, where M most often stands for Co, Ni or CoNi base. During their service under combined heat and oxygen load, a reaction zone is formed at the interface between the YSZ insulation and the metallic bond layer. The reaction zone consists of thermally grown transition metal oxides (TGO) like (Cr, Al)2O3, (Ni, Co)(Cr, Al)2O4, NiO and a-Al2O3. A dense, slow growing a-Al2O3 is beneficial for the TBC system due to its barrier effect on oxygen diffusion. Furthermore, its thermal expansion coefficient is within the range of the ceramic top coat and the metallic bond coat layer. However, the simultaneously grown other oxides can lead to increased interfacial stresses followed by micro and macro cracks and consequently by spalling of the insulation layer. In the present study, thin amorphous Al and AlOx films were deposited by DC-magnetron sputtering on the as-sprayed of CoNiCrAlY metallic bond coat. They act as thin interlayer between the bond coat and thermally sprayed YSZ top coat. The coating systems were characterised concerning surface morphology, microstructure and thermal cycling behaviour. Also, the effect on the constitution and the thickness of the TGO was investigated. As a result, the applied thin metallic Al interlayer fully transforms into a defined thin aluminium oxide film at the interface of the bond coat and top coat as well as showed stability under thermal cycling. This in-situ formed dense oxide layer obviously acts as a diffusion barrier for oxygen. The same result was observed for the directly applied AlOx coating. Therefore, both interlayers have the potential to reduce the formation of detrimental oxides and hence to extend the systems durability. |