Accession Number : ADA303961

Title :   Microstructural and Strength Stability of a Developmental CVD SiC Fiber.

Descriptive Note : Technical memo.,

Corporate Author : NATIONAL AERONAUTICS AND SPACE ADMINISTRATION CLEVELAND OH LEWIS RESEARCH CEN TER

Personal Author(s) : Bhatt, Ramakrishna T. ; Garg, Anita ; Hull, David R.

PDF Url : ADA303961

Report Date : SEP 1995

Pagination or Media Count : 14

Abstract : The effects of thermal exposure on the room temperature tensile strength and microstructure of a developmental 50 microns CVD SiC fiber have been studied. The fibers were heat treated between 600 and 2000 C in 0.1 MPa argon and air environments for up to 100 hr. In the as-fabricated condition, the fibers showed approx. 6 GPa tensile strength. After argon treatment, the fibers showed strength degradation after 1 hr exposure beyond 1000 C, but those exposed between 1600 and 2000 C retained approx. 2 GPa strength. TEM results showed microstructural changes both in the surface coating and SiC sheath. Flaws created by the rearrangement of carbon in the surface coating and growth of equiaxed SiC grain zone in the SiC sheath are the suggested mechanisms of strength degradation. After air treatment, fibers showed strength degradation after only 2 min exposure at 600 deg C. Strength retention after 2 min at 1500 deg C was approx. 2 GPa. Oxidation of the surface coating is the primary reason for strength degradation. (MM)

Descriptors :   *FIBER REINFORCED COMPOSITES, *SILICON CARBIDES, METALS, FIBERS, TENSILE STRENGTH, MICROSTRUCTURE, DEGRADATION, HIGH TEMPERATURE, SURFACE FINISHING, CERAMIC MATRIX COMPOSITES, THERMAL STABILITY, CHEMICAL VAPOR DEPOSITION, METAL MATRIX COMPOSITES, CARBON, STRENGTH(MECHANICS), COATINGS, OXIDATION, ARGON, REINFORCING MATERIALS.

Subject Categories : Laminates and Composite Materials

Distribution Statement : APPROVED FOR PUBLIC RELEASE