Thermal stability of Hi-Nicalon SiC fiber in nitrogen and silicon environments

Conference · Fri Sep 01 04:00:00 EDT 1995

OSTI ID:188450

Bhatt, R T; Garg, A

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 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 uncoated and coated fibers embedded in silicon powder and exposed to 0.1 MPa N2 for 24 hrs at temperatures to 1400 C was investigated. The uncoated and both types of BN coated fibers exposed to N2 for 1 hr showed noticeable strength degradation above 1400 C and 1600 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 C.

• Research Organization: National Aeronautics and Space Administration, Cleveland, OH (United States). Lewis Research Center
• OSTI ID: 188450
• Report Number(s): N--96-16596; NASA-TM--106987; E--9761; NAS--1.15:106987; ARL-TR--879; CONF-950833--; CNN: RTOP 505-63-12
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
BORON NITRIDES
COATINGS
FIBERS
HEAT TREATMENTS
SILICON CARBIDES
TENSILE PROPERTIES
THERMAL DEGRADATION