X-RAY TOMOGRAPHIC STUDY OF CHEMICAL VAPOR INFILTRATION PROCESSING OF CERAMIC COMPOSITES

The fabrication of improved ceramic-matrix composites will require a b etter understanding of processing variables and how they control the d evelopment of the composite microstructure. Noninvasive, high-resoluti on methods of x-ray tomography have been used to measure the growth of silicon carbide in a woven Nicalon-fiber composite during chemical va por infiltration. The high spatial resolution allows one to measure th e densification within individual fiber tows and to follow the closure of macroscopic pores in situ. The experiments provide a direct test o f a recently proposed model that describes how the surface area availa ble for matrix deposition changes during infiltration. The measurement s indicate that this surface area is independent of the fiber architec ture and location within the preform and is dominated by large-scale m acroporosity during the final stages of composite consolidation. The m easured surface areas are in good agreement with the theoretical model .