A comparative study of TiN and TiC: Oxidation resistance and retention of xenon at high temperature and under degraded vacuum

摘要

Dense TiN and TiC samples were prepared by hot pressing using micrometric powders. Xenon species (simulating rare gas fission products) were then implanted into the ceramics. The samples were annealed for 1 h at 1500 ℃ under several degraded vacuums with P_O_2 varying from 10~(-6) to 2 × 10~(-4) mbars. The oxidation resistance of the samples and their retention properties with respect to preimplanted xenon species were analyzed using scanning electron microscopy, grazing incidence x-ray diffraction, Rutherford backscattering spectrometry, and nuclear backscattering spectrometry. Results indicate that TiC is resistant to oxidation and does not release xenon for P_O_2 ≤ 6 × 10~(-6) mbars. When P_O_2 increases, geometric oxide crystallites appear at the surface depending on the orientation and size of TiC grains. These oxide phases are Ti_2O_3, Ti_3O_5, and TiO_2. Apparition of oxide crystallites is associated with the beginning of xenon release. TiC surface is completely covered by the oxide phases at P_O_2=2 × 10~(-4) mbars up to a depth of 3 μm and the xenon is then completely released. For TiN samples, the results show a progressive apparition of oxide crystallites (Ti_3O_5 mainly) at the surface when P_O_2 increases. The presence of the oxide crystallites is also directly correlated with xenon release, the more oxide crystallites are growing the more xenon is released. TiN surface, is completely covered by an oxide layer at P_O_2 =2 × 10~(-4) mbars up to 1 μm. A correlation between the initial fine microstructure of TiN and the properties of the growing layer is suggested.