Interfacial Characterization of Glass and Glass-Ceramic Matrix/Nicalon SiC Fiber Composites

Abstract

The strong and tough composite systems consisting of Nicalon SiC yarn reinforced lithium aluminosilicate (LAS) glass-ceramics, with and without Nb₂O₅ additive as a means to form a NbC reaction layer around the SiC fibers during fabrication, have been characterized through the use of TEM replica and thin foil analysis and scanning Auger microprobe (SAM) analysis of composite fracture surfaces. From these studies, it has been found that the chemistry of the fibers within a few hundred angstroms of the fiber/matrix interface has changed significantly from as-received fibers in that a carbon rich zone of 100–400Å in thickness has formed at the fiber surface and that aluminum has diffused into the fibers from the glass-ceramic matrix.

From SAM analysis of Nicalon fiber surfaces from extremely weak and brittle glass and glass-ceramic matrix composites, this carbon rich layer is either nonexistent or much reduced in carbon content. It appears, therefore, that the formation of this carbon rich interfacial zone in the LAS matrix composites under study leads to quite weak bonding at the fiber/matrix interface that directly contributes to the high toughness observed for these materials.