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Silicon nitride materials featured by superior creep and fracture resistance at 1400 degree

Siliziumnitridwerkstoffe mit hohem Kriech- und Bruchwiderstand bei 1400 degree
: Klemm, H.; Herrmann, M.; Reich, T.; Schubert, C.

American Ceramic Society -ACerS-, Westerville/Ohio:
96th Annual Meeting and Exposition of the American Ceramic Society 1994
Westerville/Ohio, 1994
American Ceramic Society (Meeting) <96, 1994, Indianapolis>
Conference Paper
Fraunhofer IKTS ()
Bruchzähigkeit; creep; fracture thoughness; Gefüge; grain boundary composition; high temperature; hohe Temperatur; Korngrenzenzusammensetzung; Kriechen; microstructure; silicon nitride; Siliziumnitrid; subcritical crack growth; unterkritische Rissausbreitung

The mechanical behaviour of different silicon nitride materials were evaluated with emphasis placed on the high temperature properties as like creep, subcritical crack growth defect sensibility and fracture resistance on the one hand and the room temperature properties and their densification on the other hand. Materials containing only Si02 or only very small amounts of additives exhibit superior high temperature properties but they am very sensitive to defects and difficult to densify (only by encapsulation HIP). The parameter that enhance densification or cause an increase in flaw tolerance and fracture resistance at room temperature as well as at 1400 degree (microstructure with elongated grains, grain boundary softening at lower temperatures) are the same ones that promote property degradation at elevated temperatures (creep and SCG-resistance). A possible way to overcome this problem is given by investigations on mixed alpha-beta-Sialons and Si3N4-SiC nanocomposites which show bo th a very small defect sensibility with a high fracture resistance and a superior creep behaviour at 1400 degree (epsilon (200MPa) smaller than 10-5 h-1).