X-ray Tomographic Study of Chemical Vapor Infiltration Processing of Ceramic Composites

Abstract

The fabrication of improved ceramic-matrix composites will require a better understanding of processing variables and how they control the development of the composite microstructure. Noninvasive, high-resolution methods of x-ray tomography have been used to measure the growth of silicon carbide in a woven Nicalon-fiber composite during chemical vapor infiltration. The high spatial resolution allows one to measure the densification within individual fiber tows and to follow the closure of macroscopic pores in situ. The experiments provide a direct test of a recently proposed model that describes how the surface area available for matrix deposition changes during infiltration. The measurements indicate that this surface area is independent of the fiber architecture and location within the preform and is dominated by large-scale macroporosity during the final stages of composite consolidation. The measured surface areas are in good agreement with the theoretical model.

Direct 3D microscale imaging of carbon–carbon composites with computed holotomography

“…X-ray tomography appears as an ideal technique for nondestructive characterization at the different pore scales of 3D microstructure. Absorption tomography has already been used successfully to characterize the structure of SiC fiber cloth layup preforms at macro-porosity scale (pixel size of 15.6 µm) [3,4]. In this method, the image contrast results from the difference between the X-ray attenuation coefficient of the phases (porosity, fiber and deposit).…”

Fibre-scale Modeling of C/C Processing by Chemical Vapour Infiltration using Xray CMT Images and Random Walkers

“…Two approaches are then possible: first, the complete refraction index reconstruction, called holotomography (14), and second, the phase-contrast edge-detection mode, associated to image processing for the segmentation of the constitutive phases. These extra difficulties partly explain why there has been a large time gap between the first successful characterizations of the structure of SiC fiber cloth lay-up preforms at bundle scale (pixel size of 15.6 mm) (15,16) and the same kind of work on C/C composites.…”

Stochastic Virtual Tests for High-Temperature Ceramic Matrix Composites

“…Investigators have measured characteristics of textile geometry and tow deformation (8,13,55), as well as porosity (56) and its changes during processing steps (56,57). The same technique is now yielding 3D images of damage captured in situ under load at very high temperatures, which is key to informing simulations of damage evolution (58).…”