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a b s t r a c tThe evolution of hardness and elastic modulus with temperature for silicon carbide (SiC) coatings in tristructural-isotropic fuel was measured by in-situ nanoindentation from ambient temperature up to 500 C. Over this temperature range a significant drop in SiC hardness was identified, whereas the elastic modulus decreased only slightly with increasing temperature. The SiC coatings that had been irradiated in the High Flux Reactor in the 'PYCASSO' experiment exhibited irradiation hardening.

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The elastic modulus and hardness of different silicon carbide (SiC) coatings in tristructural-isotropic (TRISO) fuel particles were measured by in situ high temperature nanoindentation up to 500°C. Three samples fabricated by different research institutions were compared. Due to varied fabrication parameters the samples exhibited different grain sizes and one contained some visible porosity. However, irrespective of the microstructural features in each case the hardness was found to be very similar in the three coatings around 35 GPa at room temperature. Compared with the significantly coarser grained bulk CVD SiC, the drop in hardness with temperature was less pronounced for TRISO particles, suggesting that the presence of grain boundaries impeded plastic deformation. The elastic modulus differed for the three TRISO coatings with room temperature values ranging from 340 to 400 GPa. With increasing measurement temperature the elastic modulus showed a continuous decrease.

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