Accession Number:

ADA224968

Title:

Influence of Interfacial Shear Strength on the Mechanical Properties of SiC Fiber Reinforced Reaction-Bonded Silicon Nitride Matrix Composites

Descriptive Note:

Technical memo.

Corporate Author:

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION CLEVELAND OH LEWIS RESEARCH CENTER

Personal Author(s):

Report Date:

1990-01-01

Pagination or Media Count:

15.0

Abstract:

The influence of fibermatrix interface microstructure and interfacial shear strength on the mechanical properties of a fiber-reinforced ceramic composite has been evaluated. The composite consisted of about 30 vol uniaxially aligned 142 micron diameter SiC fibers Textron SCS-6 in a reaction- bonded Si3N4 matrix SiCRBSN. The interface microstructure was varied by controlling the composite fabrication conditions and by heat treating the composite in an oxidizing environment. Interfacial shear strength was determined by the matrix crack spacing method. The results of microstructural examination indicate that the carbon-rich coating provided with the as-produced SiC fibers was stable in composites fabricated at 1200 C in a nitrogen or in a nitrogen plus 4 percent hydrogen mixture for 40 hr. However this coating degraded in composites fabricated at 1350 C in N2 4H2 for 40 and 72 hr and also in composites heat treated in an oxidizing environment at 600 C for 100 hr after fabrication at 1200 C in a nitrogen. It was determined that degradation occurred by carbon removal which in turn had a strong influence on interfacial shear strength and other mechanical properties. Specifically, as the carbon coating was removed, the composite interfacial shear strength, primary elastic modulus, first matrix cracking stress, and ultimate tensile strength decreased, but the first matrix cracking strain remained nearly the same. Keywords Ceramic matrix composites Interfacial shear strength Mechanical properties.

Subject Categories:

  • Laminates and Composite Materials

Distribution Statement:

APPROVED FOR PUBLIC RELEASE