Development of oxide based diffusion barrier coatings for CFC components applied in modern furnaces

Abstract

Carbon fibre reinforced carbon (CFC) materials show a high potential for usage in furnaces as sample carriers for example, which is due to their excellent thermal stability compared to steel carriers. Only their tendency to react with different metals at high temperatures by C-diffusion is a disadvantage, which can be solved by application of diffusion barriers. In order to enable the utilization of CFC-carriers for e.g. brazing furnaces, within the frame of this study thermally sprayed diffusion barrier coatings were developed. Coatings of mullite and ZrO₂-7%βY₂O₃ (YSZ) were prepared by air plasma spraying (APS). The coatings were investigated in terms of their microstructure and thermal shock behaviour. In order to prove the suitability of the coatings for the application in brazing furnaces, the wettability of the coating surfaces by a Ni-based brazing alloy was investigated. The results showed that both mullite and YSZ could be deposited on CFC substrates with a bond coat of W or SiC. Both coatings exhibited good thermal shock behaviour and an excellent non-wetting behaviour against the used Ni-based braze alloy.

Keywords

diffusion barrier coatings / carbon fibre reinforced carbon (CFC) / plasma spraying / microstructure / furnace

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Acknowlegdements

This work was funded with budget funds of the Federal Ministries of Economics and Technology (BMWi) via the German Federation of Industrial Research Associations “Otto von Guericke” e.V. (AiF) (IGF-Nr.: 14.880 N/DVS-Nr.: 2.050) and supported by the Research Association of the German Welding Society (DVS). The authors would like to thank all parties involved for the funding and the support.

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2014 Higher Education Press and Springer-Verlag Berlin Heidelberg