Fiber-Matrix Interphase Development in Carbon/Carbon Composites

摘要

In carbon/carbon (C/C) composites-i.e., a composite in which a carbon matrix isreinforced with carbon fiber when the matrix is derived from a thermosetting resin, we always observe a distinct, highly graphitizable, and well-oriented matrix interphase structure adjacent to the fibers. Qualitatively, the orientation of the interphase is the same as the fiber. The structure of this interphase becomes more prominent, i.e., more graphitic, as the heat treatment exceeds about 2200 deg C. Specifically, we have hypothesized that the critical factor for development of lamellar graphite (by subsequent high temperature heat treatment) in this interphase, rather than amorphous glassy carbon, is a state of multiaxial tensile deformation during pyrolysis. We have studied the structural details of the interphase region in more detail using transmission electron microscopy in conjunction with selected area (electron) diffraction (SAD). We have also examined the influence of matrix microstructure on fracture behavior by using an in situ SEM flexure stage that allowed us to follow the crack tip as it advanced through the different microstructural regions. The development of a graphitized carbon interphase can have major effects on properties. Two are discussed in this publication. The first is the effect on matrix density and associated matrix shrinkage. The other is the effect on mechanical properties.