Heat treatment effects on microstructure of SiC fiber preforms. Technical memo
Technical Report
·
OSTI ID:698746
Preforms of BN/SiC coated Sylramic SiC fibers were heat treated at 1420 deg, 1600 deg, and 1800 deg C in 0.1 MPa argon or at 1800 deg C in 103 MPa nitrogen for 1 h. Optical, SEM, and TEM techniques were used to analyze the effects of environmental exposure on constituent microstructure of the preforms. TEM analysis of the as-received preforms indicates that the CVI BN coating is predominantly amorphous with small amounts of microcrystalline BN grains, and that the SiC coating on top of the BN coating and SiC fibers is polycrystalline. With increasing temperature of exposure from 1420 deg to 1800 deg C, the preforms heat treated in argon showed increasing amounts of crystalline BN in the CVI BN coating, and coarsening of SiC grains in the CVI SiC coating and SiC fibers. On the other hand, the preforms heal treated in 103 MPa nitrogen at 1800 deg C for 1 h showed microstructural changes inside the fiber tows similar to those heat treated at 1800 deg C in 0.1 MPa argon for 1 h, but the same preforms on the outer periphery of the tows showed reaction between nitrogen and the CVI SiC coating to form Si3N4.
- Research Organization:
- National Aeronautics and Space Administration, John H. Glenn Research Center, Cleveland, OH (United States); Dynacs Engineering Co., Inc., Cleveland, OH (United States)
- OSTI ID:
- 698746
- Report Number(s):
- AD-A--367099/XAB
- Country of Publication:
- United States
- Language:
- English
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