Irradiation-induced dimensional changes in co-deposited carbon-silicon coatings

Abstract

Irradiations of pure and silicon-alloyed isotropic carbons (deposited below 1500°C) at 910°–1300°C to fast-neutron fluences in the range 1.4–4.8 × 10 21 n/ cm 2 ( E > 0.18 MeV) show that silicon concentrations above about 18 wt-% are effective in reducing the irradiation-induced dimensional changes. For example, at 910°C the lineal shrinkages caused by irradiation are reduced about a factor of 3 by the addition of 34 wt-% silicon. At 1250° to 1300°C the corresponding reduction is about a factor of 2. At 910°C, irradiation creep strains as high as 5.5% per 10 21 n/cm 2 were measured for the unalloyed carbons. At 1250°–1300°C, total creep strains of 10 per cent were observed for unalloyed carbons, and 8 per cent were observed for the alloyed coatings. Since none of the creep specimens fractured, these are not limiting values. Comparison data for isotropic carbons deposited below 1500°C (LTI carbons) with those for isotropic carbons deposited above 1500°C (HTI carbons) shows that at high fluences the LTI carbons expand at a rate that is substantially less than the corresponding rate for HTI carbons.