Abstract No.:
2693

 Title:
Thermal barrier coatings on novel high temperature cobalt rhenium substrates

 Authors:
Philipp Seiler* / Institut für Werkstoffe Technische Universität Braunschweig, Germany
Martin Bäker / Institut für Werkstoffe, TU Braunschweig, Germany
Joachim Rösler/ Institut für Werkstoffe, TU Braunschweig, Germany

 Abstract:
Nowadays, highly stressed components in gas turbines are made of nickel based alloys, which limit the typical service temperature to 1100°C. Increasing the service temperature beyond 1200°C increases the efficiency of the turbine itself. For these temperatures cobalt rhenium (CoRe) alloys are suitable which is due to the 250°C higher melting temperature compared to nickel based alloys. The used substrates are protected against the high gas temperatures by thermal barrier coating systems. A typical coating system consists of the bond coat, the thermally grown oxide (TGO) and the ceramic top coat.

For CoRe substrates CoReCrSi is a promising bond-coat material. CoReCrSi is thermo-chemically compatible to CoRe substrates due to the very similar mechanical and chemical properties. Furthermore, it may form a dense chromium oxide or silicon oxide layer. The oxide formation and the adhesion of the top coat on CoReCrSi is determined by studying a simplified coating system. This coating system consists of a CoReCrSi bond coat bulk material, and a yttria-stabilised zirconia on top. The model system is tested under cyclic conditions at 1200°C.

This study provides a first insight into the TGO growth, the basic failure mechanism of the top coat, and the diffusion processes at the top coat/bond coat interface. It is shown that CoReCrSi with 2 at.% silicon promotes a good adhesion of the top coat by forming a dense chromium oxide layer. The critical TGO thickness beyond which the TGO fails by spallation was determined as 25 microns and is roughly 2.5 times the critical thickness of MCrAlY. Higher amounts of silicon leads to inner oxidation of the bond coat and early spallation of the top coat.


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