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Effect of long-term oxidation on creep and failure of Si3N4 and Si3N4/SiC nanocomposites

Einfluß der Langzeit-Oxidation auf das Kriechen und Versagen von Si3N4 und von Si3N4/SiC-Nanoverbundwerkstoffen
: Rendtel, P.; Rendtel, A.; Hübner, H.; Klemm, H.; Herrmann, M.


Journal of the European Ceramic Society 19 (1999), Nr.2, S.217-226
ISSN: 0955-2219
Fraunhofer IKTS ()
Si3N4; composites; oxidation; creep behaviour; lifetime

The high-temperature mechanical behaviour of an Si3N4/SiC nanocomposite and its monolithic Si3N4 reference material was studied after long-term oxidation treatments intended to simulate future operating conditions in a severe environment. Creep and failure at elevated temperature were significantly affected, in the direction of increased brittleness. The transition stress between the ductile range present at low stresses and the brittle range existing at high stresses was shifted to distinctly lower values. The creep resistance in the low-stress range was increased by the oxidation treatment. The failure time under a given stress was drastically reduced; this was attributed to an increased sensitivity to subcritical crack growth. The failure stress for a given failure time was decreased by about half. The phenomena are explained in terms of a purification of the intergranular phase and by the formation of surface defects and of a uniformly distributed pore population.