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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.

Laser induced damage initiation on fused silica optics can limit the lifetime of the components when used in high power Uv laser environments. Foe example in inertial confinement fusion research applications, the optics can be exposed to temporal laser pulses of about 3-nsec with average fluences of 8 J/cm2 and peak fluences between 1 2 and 1 5 J/cm2. During the past year, we have focused on optimizing the damage performance at a wavelength of 355-nm (3w), 3-nsec pulse length , for optics in this category by examining a variety of finishing technologies with a challenge to improve the laser damage initiation density by at least two orders of magnitude. In this paper, we describe recent advances in improving the 30) damage initiation performance of laboratory-scale zirconium oxide and cerium oxide conventionally finished fused silica optics via application of processes incorporating magnetorheological finishing (MRF), wet chemical etching, and UV laser conditioning. Details of the advanced finishing procedures are described and comparisons are made between the procedures based upon large area 3w damage performance, polishing layer contamination, and optical subsurface damage. Downloaded From: http://proceedings.spiedigitallibrary.org/ on 09/19/2013 Terms of Use: http://spiedl.org/terms Proc. SPIE Vol. 4679 57 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 09/19/2013 Terms of Use: http://spiedl.org/terms