Interfacial Chemistry and Bonding in Fiber Reinforced Glass and Glass-Ceramic Matrix Composites

Abstract

The fiber/matrix interfacial region between Nicalon Si-C-O fibers and a variety of glass and glass-ceramic matrices was examined, primarily through the use of the scanning transmission electron microscope (STEM) and the Scanning Auger Multiprobe (SAM). From the analyses of strong and fracture tough composites, it was found that the chemistry of the Nicalon fibers within a few hundred angstroms of the fiber surface undergoes a rather profound change when the fibers are incorporated into certain glass or glass-ceramic matrices. Among the changes noted for certain lithium aluminosilicate (LAS) glass-ceramic and aluminosilicate glass matrix composites is that a thin (~500Ǻ) interfacial zone forms that is extremely carbon rich, being almost totally devoid of Si and O. From SAM analysis of Nicalon fiber surfaces from extremely weak and brittle glass and glass-ceramic matrix composites where the fiber and matrix appear to be rather strongly bonded, 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 glass and glass-ceramic matrix composites under study leads to quite weak bonding at the fiber/matrix interface that directly contributes to the high toughness observed for these systems.