Thermal Stability of Hi-Nicalon SiC Fiber in Nitrogen and Silicon Environments.
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION CLEVELAND OH LEWIS RESEARCH CEN TER
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The room temperature tensile strength of uncoated and two types of pyrolytic boron nitride coated PBN and Si-rich PBN Hi-Nicalon SiC fibers was determined after 1 to 400 hr heat treatments to 1800 deg C under N2 pressures of 0.1,2, and 4 MPa, and under 0.1 MPa argon and vacuum environments. In addition, strength stability of both the uncoated and coated fibers embedded in silicon powder and exposed to 0.1 MPa N2 for 24 hrs at temperatures to 1400 deg C was investigated. The uncoated and both types of PBN coated fibers exposed to N2 for 1 hr showed noticeable strength degradation above 1400 deg and 1600 deg C, respectively. The strength degradation appeared independent of nitrogen pressure, time of heat treatment, and surface coatings. TEM microstructural analysis suggests that flaws created due to SiC grain growth are responsible for the strength degradation. In contact with silicon powder, the uncoated and both types of PBN coated fibers degrade rapidly above 1350 deg C. jg p2
- Inorganic Chemistry
- Ceramics, Refractories and Glass
- Laminates and Composite Materials