Defect evolution in pure iron under simultaneous in-situ irradiation with Fe+-He+-H2+: Impact of hydrogen & helium-dose ratios

Abstract

The properties of materials in irradiation environments are significantly influenced by hydrogen and helium. However, the effects of gas-dose ratio on the evolution of defects, which are crucial for material application assessment in various nuclear reactors and for understanding fundamental irradiation mechanisms, remain unclear. In this paper, defect evolution within pure iron was investigated in-situ through simultaneous triple-beam irradiation at 723 K using 400 keV Fe⁺, 50 keV He⁺ and 50 keV H₂⁺. Four different gas-dose ratios were used: 10 appm He/dpa & 45 appm H/dpa, 10 appm He/dpa & 100 appm H/dpa, 100 appm He/dpa & 100 appm H/dpa, and 45 appm He/dpa & 10 appm H/dpa. It was observed that the gas-dose ratio significantly influenced the evolution of defects, including the size and density of dislocation loops and bubbles. It was found that an increased hydrogen-dose ratio, when paired with a constant helium-dose ratio, resulted in smaller loop sizes, but increased the density of loops and bubbles. Conversely, maintaining a constant hydrogen dose ratio while increasing the helium dose ratio proved advantageous for raising the density of loops and bubbles, and for reducing loop size. Additionally, an increase in both hydrogen and helium-dose ratios was associated with heightened swelling due to bubble formation. Moreover, hydrogen was found to have a less impact on loop nucleation compared to helium, and helium exhibited a more pronounced inhibitory effect on loop migration than hydrogen.