Oxidation and mechanical damage in a unidirectional SiC/Si{sub 3}N{sub 4} composite at elevated temperature
- Georgia Inst. of Tech., Atlanta, GA (United States). School of Materials Science and Engineering
The results of a study on the high-temperature damage mechanisms in a unidirectional Nicalon fiber-reinforced reaction-bonded silicon nitride (RBSN) composite are presented in this paper. The microstructure of the as-manufactured and tested specimens were characterized using a variety of techniques including: X-ray diffraction; optical, scanning, and transmission microscopy; and dilatometry. Single-edge notch specimens under three-point bend loading were tested under a constant displacement-rate conditions as well as under a sustained loading condition at 1,000 C in air. The load-line displacement was used as the in situ indicator of damage accumulation. The fracture surface and the damage zone around the main crack were characterized in the fractured specimens to investigate the high-temperature fracture mechanisms. Under constant displacement rate, the composite showed extensive nonlinear load versus displacement behavior, indicating that the presence of the fiber has indeed toughened the composite. Cracks propagated nominally along the notch plane, though some delaminations were also observed. The substantial bulk oxidation occurred even at test temperatures as low as 800 C and resulted in significant changes in the dimension of the composite specimens. The fiber pullout, fracture surface morphology, and delamination were all strongly influenced by the high-temperature oxidation.
- OSTI ID:
- 624254
- Report Number(s):
- CONF-950618--; ISBN 0-8031-2413-9
- Country of Publication:
- United States
- Language:
- English
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