48451 The application of X-ray tomographic microscopy to chemical vapor infiltration processing of ceramic matrix composites : 1991 Industrial Computed Tomography II, San Diego, California (United States), 20–24 May 1991. pp. 89–93. ASNT (1991)

Abstract

Before ceramic composite materials can be used in critical structures it will be necessary to reduce the amount of porosity which remains after processing. Complete densification of chemical vapor infiltrated (CVI) composites has yet to be attained due to the enclosure of pores by growth of the matrix on surrounding fibers. If the residual porosity cannot be significantly reduced during processing, much of the anticipated fracture toughness of Ceramic Matrix Composites (CMCs) may be lost. Clearly, a noninvasive technique is required for making dynamic observations of matrix growth during CVI processing. Though there are many NDE techniques which might be applied to pore characterization, all of them have drawbacks when imaging complex, overlapping microstructures. For example, techniques such as fluorescent penetrant and infrared inspection reveal only surface flaws and cannot be applied universally to all classes of materials. X-ray tomographic microscopy (XTM) is a high resolution, noninvasive technique which is ideally suited for imaging materials microstructures in three-dimensions. XTM allows imaging of microporosity between individual filaments in the fiber bundles, measurement of channel porosity between individual cloth layers, and characterization of the interconnectivity of the large through-ply holes that remain after processing. This paper reports the results of an XTMmore » study on unreacted fiber preforms and fully dense CMCs with the express purpose of demonstrating that XTM has the spatial resolution and the contrast sensitivity to measure the important microstructural features in these materials. 4 figs.« less