LOW-DOSE IRRADIATION PERFORMANCE OF SIC INTERPHASE SIC SIC COMPOSITES/

Reduced oxygen Hi-Nicalon(TM) fiber reinforced composite SiC materials were densified with a chemically vapor infiltrated (CVI) silicon carb ide (SiC) matrix and interphases of either 'porous' SiC or multilayer SiC and irradiated to a neutron fluence of 1.1 x 10(25) n m(-2) (E > 0 .1 MeV) in the temperature range of 260 to 1060 degrees C. The unirrad iated properties of these composites are superior to previously studie d ceramic grade Nicalon fiber reinforced/carbon interphase materials. Negligible reduction in the macroscopic matrix microcracking stress wa s observed after irradiation for the multilayer SiC interphase materia l and a slight reduction in matrix microcracking stress was observed f or the composite with porous SiC interphase. The reduction in strength for the porous SiC interfacial material is greatest for the highest i rradiation temperature, The ultimate fracture stress (in four point be nding) following irradiation For the multilayer SiC and porous SiC int erphase materials was reduced by 15% and 30%, respectively, which is a n improvement over the 40% reduction suffered by irradiated ceramic gr ade Nicalon fiber materials fabricated in a similar fashion, though wi th a carbon interphase. The degradation of the mechanical properties o f these composites is analyzed by comparison with the irradiation beha vior of bare Hi-Nicalon fiber and Morton chemically vapor deposited (C VD) SIG. It is concluded that the degradation of these composites, as with the previous generation ceramic grade Nicalon fiber materials, is dominated by interfacial effects, though the overall degradation ol-f iber and hence composite is reduced for the newer low-oxygen fiber. (C ) 1998 Elsevier Science B.V.