Diffusion and retention of helium in titanium carbide
Résumé
The knowledge of helium migration in TiC is an important issue due to its possible use as fuel coating in fission reactors and as first wall material coating in fusion reactors. Helium release measurements and diffusion coefficient calculations of helium in polycrystalline TiC have been carried out in the temperature range (1000–1600 °C) for the time period of 2 h. Polished bars of TiC were implanted with 3 MeV $^3$He$^+$ ions in normal incidence at a dose of 5 × 10$^{20}$ at./m$^2$ at room temperature. Helium depth profile was measured at each step using the $^3$He(d, p$_0$)$^4$He nuclear reaction by varying the incident deuteron energy from 900 to 1800 keV. Effective diffusion coefficients vary from 4.20 × 10$^{−18}$ to 2.59 × 10$^{−17}$ m$^2$ s$^{−1}$ and activation energy values obtained are in the range 0.8–2.5 eV. Due to scarce availability of stoichiometric TiC, challenges in this study came from native vacancies present in the samples. The helium distribution and its release were affected by the presence of grain boundaries. He is considered to undergo two distinct populations into the sample and different values of diffusion coefficient have been determined for each population.