Influence of carbon on the evolution of irradiation defects in tungsten

Abstract

We have systematically investigated the influence of carbon (C) impurity on the aggregation, migration, and annihilation of neutron irradiation defects as well as the mechanical properties of tungsten (W), based on the object kinetic Monte Carlo (OKMC) calculations in combination with the theoretical models. Interestingly, although C has a strong attraction with both vacancy-type and interstitial-type irradiation defects, the C addition promotes the aggregation of former but inhibits latter in W. On the one hand, due to the weak repulsion of di-vacancy, it is difficult to form vacancy clusters spontaneously. However, the presence of C changes the interaction between vacancies from repulsion to attraction, thus promoting their clustering in W and leading to the increase of average size of vacancies cluster. On the other hand, because of the strong attraction, self-interstitial atoms (SIAs) tend to form clusters spontaneously. However, the C addition will slow down the diffusivity of SIAs due to the strong attraction between them, thereby blocking the aggregation of interstitial-type defects. Therefore, the number density of SIA clusters will increase with the increasing of C concentration, but the average size decreases significantly. Besides, the influence of C on the annihilation ratio of neutron irradiation defects is dependent on the temperature, which is mainly because the stability of C-SIA complexes and the migration of vacancies are strongly temperature dependent. Further, it is found that the increment of Vickers hardness in irradiated W at low temperature increases with the increasing of C concentration, which should be attributed to the enhanced effect of C on the retention of irradiation defects. When the C concentration is 2.5–5 appm, the model predictions are consistent with the experimental results. Consequently, although the concentration of impurity is extremely low in nuclear materials, it has significant effect on the defect evolution and mechanical properties under irradiation.