Investigation of silicon carbide composites as structural materials for nuclear applications.

摘要

The motivation for this thesis work was to explore the potential for using silicon carbide (SiC) composite materials in fusion reactors. To this point there are no commercial uses of silicon carbide composites for structural applications, and very little is known regarding the behavior of such systems under irradiation. The use of this material as a load bearing structure in a fusion system, which is an extremely demanding environment even for well understood structural materials, is highly speculative.; Because so little is know about the radiation response of ceramic matrix composites, a large part of this thesis was devoted to the development of techniques to evaluate irradiated composite behavior. A single composite system has been chosen for this study, namely the chemically vapor infiltrated SiC/Nicalon fiber reinforced composite. Microstructural and micromechanical testing following both ion beam and fission neutron irradiations are presented. It is shown that this system is substantially degraded in strength following fission irradiation to 1 displacement per atom. Through inspection of the composite elements with transmission microscopy and micromechanical testing it is found that the reason for the degradation is due primarily to fiber/matrix interfacial debonding. Such debonding inhibits the composites ability to transfer load between the matrix and the high strength reinforcement thereby reducing the systems ultimate load capability. The most likely cause for this debonding is shrinkage of the Nicalon silicon carbide based fiber. For this reason it has been concluded that the immediate obstacle for the use of SiC composites in nuclear systems is the development of a more radiation stable fiber.