Synergies between H and He in advanced F/M steels for fusion reactors and spallation target

A comparative study was conducted to investigate the synergistic effects of H and He on the microstructure evolution, irradiation swelling, and hardening of two candidate ferritic/martensitic steels (SIMP and T91) for fusion reactors and spallation target. Ion irradiation experiments were carried out using mixed H₂⁺/He²⁺ beams with doses of 4 × 10¹⁷ H₂⁺/cm² and 1 × 10¹⁷ He²⁺/cm², at irradiation temperatures of RT, 300 °C, and 500 °C. The results reveal that at low temperatures, H and He interacted to form stable HHe-vacancy clusters, promoting uniform cavity nucleation. As the temperature increases, the cavities were more heterogeneously distributed, particularly at grain boundaries (GBs) and dislocations. Notably, SIMP exhibited superior resistance to irradiation swelling compared to T91, likely due to its finer microstructure and higher silicon content. The study also shows that the hardening of SIMP was more pronounced than T91, correlating with larger size and higher density of dislocation loops (DLs). The irradiation hardening decreased with increasing temperature. These findings reveal a temperature-sensitive synergy between H and He, emphasizing its significance for material design in fusion and spallation environments.