Defect production in tungsten under sub-threshold energy irradiation: role of hydrogen and surface effects

• Published in: Nuclear Fusion
• Main Authors: Hao-Xuan Huang, Yu-Hao Li, Jin-Liang Li, Fang-Fei Ma, Qing-Yuan Ren, Li-Min Liu, Hong-Bo Zhou, Guang-Hong Lu
• Format: Article
• Language: English
• Published: IOP Publishing 2024-01-01
• Subjects: defect production; sub-threshold energy; hydrogen supersaturation; tungsten; molecular dynamics
• Online Access: https://doi.org/10.1088/1741-4326/ad3091

Despite the low solubility of hydrogen isotopes (HIs) in tungsten (W), their concentration can reach up to ∼10 at.% after low-energy plasma irradiation. This is generally attributed to the vacancies that may accommodate excessive HIs. However, the kinetic energy of incident HIs transferred to W is far below the energy threshold to create a Frenkel pair, the underlying mechanism of defect production is still unclear. Here, we investigate the influence of H on the defect production in W using the molecular dynamic (MD) simulations. It is found that the threshold displacement energy (TDE) in bulk W slight decreases with the increasing of H concentration. This is due to the formation of H-vacancy complexes, which prevents the vacancy-interstitial recombination. More importantly, the H effects are significantly magnified in the surface region. On the one hand, the maximum kinetic energy transferred from 400 eV H to W can reach up to ∼21 eV due to the double-hit process, which is two times higher than that predicted by elastic collision model. On the other hand, the momentum transferred to W is completely random, including both the recoil direction upward and downward from the surface. Accordingly, the lowest TDE in W surface is only 15–21 eV at sub-surface layers with the depth of 6.7–11.1 Å, which is lower than the maximum kinetic energy transferred to W. Therefore, the low-energy HIs irradiation can create the defects in W surface directly. Our findings provide deep insight into defect production in W at sub-threshold energy and have wider implications for materials performance under low-energy ions irradiation.