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Subcritical crack growth in SiC based composites is controlled by fiber creep processes. This lifetime limiting mechanism is of special concern under irradiation as it can enhance creep related mechanisms. To evaluate the impact of irradiation on the mechanical behavior of Tyranno SA3 fibers, in situ tensile tests were conducted on single fibers. These tests were conducted under irradiation with 92 MeV Xe23+ ions at 1000 °C for different ion fluxes and stress loads using a dedicated experimental facility. It has been found that irradiation induces time-dependent deformation of the fibers under conditions where thermal creep is negligible, i.e., 300 MPa and 1000 °C. Irradiation strain rate shows linear dependence with the ion beam flux and square root dependence with the applied stress. Finally, the irradiation creep compliance is estimated to be 1.01 × 10−5 MPa−1 dpa−1.
Carbide ceramics as SiC, TiC or ZrC are potential candidates for high temperature applications such as fourth generation nuclear plants because of their refractory or low activation under neutron irradiation properties. Nevertheless, the typical drawbacks of hard ceramics (brittleness) could limit their use in these applications. In order to overcome these problems, one possibility is to decrease the grain size down to the nanometric scale. Enhancement of the mechanical properties is actually expected in such nanostructured ceramics (ductility) and moreover, these nanomaterials could also take advantage of their strong grain boundaries density to withstand severe irradiation conditions. If one wants to quantify the expected enhancement of the properties, the first challenge that has to be faced is the elaboration of the nanostructured ceramics samples. That means being able to synthesize the pre-ceramics nanopowders in weighable amounts, and then finding an efficient way to sinter them aiming at the maximum densification together with avoiding grain growth.
In this contribution, we present SiC, TiC and ZrC nanopowders synthesis by laser pyrolysis and inductively coupled plasma, together with their densification by different techniques (Hot Isostatic Pressing, Spark Plasma Sintering, High Pressure Flash Sintering). We also report the latest findings obtained on the behavior of SiC nanostructured ceramics under low energy ion irradiation.
Raw micrometric SiC and ZrC powders were used as precursors in the inductively coupled plasma experiment. The production was as high as 1 kg.h-1, with nanograins ranging from 10 to 100 nm in size depending on the synthesis conditions. For the laser pyrolysis method, gaseous precursors (SiH4, C2H2) were used for SiC while liquid alkoxides precursors were used for TiC and ZrC respectively. For SiC, the production rate can reach 100 g.h-1 (laboratory scale) with grain sizes ranging from 10 to 50 nm with narrow size distribution. For TiC and ZrC nanopowders, the production rate is lower than for SiC because of the use of liquid precursors that leads to a worse yield. In this latter case, the carbide phase is obtained after carburization of the laser pyrolyzed TiO2 (or ZrO2) / free carbon nanocomposites. The final carbide nanograins size is in the 50 – 80 nm range. After sintering, the obtained pellets show different characteristics depending on the starting powder and the sintering technique. With the right sintering conditions, the densification reaches 95 % without any sintering additives, with no (or limited) grain growth and no modification of the crystalline structure. Concerning the properties of the obtained nanostructured ceramics, the SiC pellets, together with the as-synthesized nanopowders, were submitted to low energy ion irradiation in order to compare their behavior to conventional SiC materials.
In the context of research on new materials for next generation nuclear reactors, it becomes more and more interesting to know what can be the advantages of nanostructured materials for such applications. In this study, we performed irradiation experiments on microstructured and nanostructured â-SiC samples, with 95 MeV Xe and 4 MeV Au ions. The structure of the samples was characterized before and after irradiation by grazing incidence X ray diffraction and Raman spectroscopy. The results showed the occurrence of a synergy between electronic and nuclear energy loss in both samples with 95 MeV Xe ions, while the nanostructured pellet was found to have a better resistance to the irradiation with 4 MeV Au ions.
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