Interphase Integrity of Neutron Irradiated SIC Composites

Abstract

AbstractSiC/SiC composites were fabricated from Hi-Nicalon™ fibers with carbon, porous SiC and multilayer SiC interphases. These materials were then irradiated in the High Flux Beam Reactor with fast neutrons at 260 and 900–1060°C to a dose of l.1×1025 n/m2 corresponding to 1.1 displacements per atom (dpa). Results are presented for bend strength of both non-irradiated and irradiated materials. Within the interphases studied the multilayer SiC interphase material showed the least degradation (8-20%) in ultimate bend stress, while porous SiC underwent the greatest degradation (∼35%). The fiber matrix interphases are studied with TEM for both non- irradiated and irradiated materials. While no irradiation induced microstructural evolution of the interphase was observed, debonding of the interphase from the fiber was observed for all cases. This debonding is attributed to tensile stresses developed at the interface due to densification of the Hi-Nicalon™ fiber. Residual stress analysis of the fiber matrix interface indicates that the irradiation-induced densification of Hi-Nicalon™ and the volumetric expansion of the CVD SiC matrix cause tensile stresses well in excess of those which can be withstood by these, or any other viable SiC composite interphase.