Effects of irradiation and post-irradiation annealing on the thermal conductivity/diffusivity of monolithic SiC and f-SiC/SiC composites

Laser flash thermal diffusivity measurements were made on high-purity monolithic CVD-SiC and 2D f-SiC(Hi-Nicalon(TM))/ICVI-SiC composite samples before and after irradiation (250-800degreesC, 4-8 dpa-SiC) and after post-irradiation annealing composite samples to 1200degreesC. For irradiated CVD-SiC, the defect concentrations at saturation were estimated to range from 25 300 appm (250degreesC) down to 940 appm (800degreesC). The transverse thermal conductivity ratios after-to-before irradiation (K-ir/K-o) determined at the irradiation temperatures ranged from: 0.044 (250degreesC) up to 0.12 (800degreesC) for irradiated CVD-SiC and 0.18 (330degreesC) up to 0.29 (800degreesC) for the irradiated Hi-Nicalon(TM) composite. Analysis of thermal diffusivity values for the Hi-Nicalon composite measured in air, argon, helium and vacuum indicated that thermal conductivity degradation occurred primarily due to point defect accumulation in the matrix component. After annealing to 1200degreesC and cooling to ambient, fiber/matrix debonding occurred due to net shrinkage in the fiber and PyC interface components. (C) 2004 Elsevier B.V. All rights reserved.