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Cross-section transmission electron microscopy was used to investigate the microstructure of polycrystalline silicon nitride (Si~NJ) and aluminum nitride (AIN) following 2 MeV Si ion irradiation at 80 and 400 K up to a fluence of 4x1020 ions/mz (maximum damage of -10 displacements per atom, dpa). A buried amorphous band was observed at both temperatures in Si~NA in the region corresponding to the peaks in the implanted ion and displacement damage. From a comparison of Si~NJ specimens irradiated at different fluences, it is concluded that the amorphization is primarily controlled by the implanted Si concentration rather than the displacement damage level. SiJNi amorphization did not occur in regions well-separated from the implanted ions for doses up to at least 3 dpa at 80 K, whereas amorphization occurred in the ion implanted region (calculated Si concentration >0.01 at.%) for damage levels as low as -0.6 dpa. The volumetric swelling associated with the amorphization of SijN~is c 10%. Amorphization was not observed in any of the irradiated AIN specimens. A moderate density of small (-3 nm) defect clusters were observed in the crystalline damaged regions of both the S i~N$ and AIN specimens at both irradiation temperatures. Aligned network dislocations were also observed in the AIN specimen irradiated to high dose at 80 K.

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Single crystal silicon carbide (SiC) has been 2 MeV silicon ion irradiated in various irradiation temperature and ion flux ranges to measure the effect of these parameters on the critical dose for amorphization. The temperature and flux range for which amorphization was observed ranged from 80 to 400 K and 0.066 to 3 × 104 dpa/s, respectively. The critical dose, Dcrit was found by locating the depth of the boundary between partially crystalline and fully amorphous material using dark field TEM from samples prepared in cross section. This depth was compared to the damage profile as calculated using the TRIM-96 code. The temperature dependence of Dcrit is found to agree well with previously reported values, though new evidence suggests a defect species becoming mobile in the 250-300 K range. Also of significance is that Dcrit was dependent on flux at 340 K, ranging from 0.79 displacements per atom at the lowest ion flux to ∼0.6 dpa at the highest flux level. The dose rate dependence of Dcrit, is compared with a chemical rate theory model previously described by the authors. It is seen that the dose rate dependence is substantially weaker than theorized. An extrapolation of the measured dose rate dependence is also compared with recent data on fast neutron amorphized SiC.

An experimental investigation of the in situ electrical conductivity of Wesgo Al995 polycrystalline alumina at approximately 450 °C has been performed at the high flux beam reactor at Brookhaven National Laboratory. The measured radiation induced conductivity (RIC) was about 10−8 S/m at an ionizing dose rate of 6000 Gy/s. No evidence for permanent radiation induced electrical degradation was observed for an applied electric field of 147 V/mm up to a dose level of ≈1.8 displacements per atom. The effect of neutron irradiation on the electrical properties of two mineral insulated cables was also investigated. The RIC in the MgO insulation of a coaxial and a triaxial cable was measured to be in the range of 6–20 ×10−8 S/m at an ionizing dose rate of ≈ 6000 Gy/s.

Carbon-carbon composite materials are used for plasma-facing applications in fusion energy devices. Next generation fusion reactors will produce high energy neutrons which damage the plasma facing materials and degrade their properties. Here the results of two irradiation experiments, HTFC-1 and -2, each containing specimens of carbon-carbon composites are described. Data are reported for the dimensional changes of the materials as a function of fluence in the range 0.5-5 dpa for an irradiation temperature of 600°C. The observed dimensional changes are analyzed in terms of the composite's architecture, fiber precursor, and graphitization temperature. Dimensional change “turnaround” behavior is observed for several of the materials. Strength is shown to increase with increasing neutron fluence for most of the carbon-carbon composites. High temperature thermal conductivity is reported for two 3D carbon-carbon composites, before and after irradiation. Irradiation reduces thermal conductivity by 60%. However, after thermal annealing at 1600°C the reduction in thermal conductivity is as little as 20%.

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