Oxidation Resistance of HfB2-SiC Coatings for Protection of Carbon Fibers Based Composites

Paper number

IAC-05-C2.3.02

Author

Dr. Lespade Pierre, EADS Astrium, France

Year

2005

Abstract

Carbon fibers based composites (C/C, C/SiC,..) are interesting materials for thermostructural applications such as heat exchangers, heat shields for probes or thermal protection systems for future reentry vehicles, because they retain their very good mechanical properties at high temperature. However, these materials require a protection when they are used under oxidising environments above 500°C, such as in earth reentry applications.
Chemical vapour deposition and plasma spraying techniques have been investigated for the last thirty years, but most of these processes are difficult to apply for large and complex parts. Many systems have been studied, mainly silicon based materials because their oxidation products lead to the formation of a fluid sealing glassy phase. Among the oxidation resistant materials, HfB2-SiC composites are known to exhibit one of the best behaviour at high temperature (~1700°C). Most of the materials manufactured to date have been bulk materials obtained by ceramic techniques. But these ceramic materials evidence a poor ability to sinter that implies to use hot pressing routes not suited for coating deposition.

A new liquid based process has been developed in this study for the elaboration of coatings as well as monoliths in the HfB2-SiC system. A specific microstructure has been obtained and was characterized using various techniques such as porosimetry, XRD, SEM, TEM, microanalysis and AES. The behaviour of such materials has been studied in the 600-1700°C temperature range in flowing O2/He mixtures (PO2= 5 to 200 mbar). The oxidation resistance up to 1700°C is discussed according to the degradation mechanisms involving compositional and microstructural changes.

Application and coating of carbon / carbon composites have been performed. First results of oxidation tests under low pressure in convective environment (COMETE facility) is also shown and discussed.

Abstract document

IAC-05-C2.3.02.pdf

Manuscript document

IAC-05-C2.3.02.pdf (🔒 authorized access only).

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