Defect evolution in Fe using in-situ Fe-H-He triple-beam simultaneous irradiation under two orders of magnitude of dose rates with constant H/dpa and He/dpa ratios

The effectiveness and reliability of ion irradiation with high damage rates and without hydrogen and helium production to simulate neutron irradiation with low damage rates and with hydrogen and helium from nuclear reactions in the study of nuclear material irradiation damage has been questioned for a long time. In this work, the evolution of dislocation loops and helium bubbles in pure Fe was examined under Fe-H-He triple-beam simultaneous irradiation with two orders of magnitude (10⁻³ dpa/s-10⁻⁵ dpa/s) changes in the irradiation damage rate while maintaining constant hydrogen & helium-dose ratios (10 appm He/dpa and 45 appm H/dpa). The in-situ TEM analysis revealed the effect of dose rate on defect nucleation/growth: higher dose rates promote high density nucleation of dislocation loops and bubbles, but inhibit their growth. Lower dose rates, on the other hand, favour continuous growth of defects, leading to larger sizes and increased expansion rates. Based on experimental data, a comprehensive prediction equation for swelling ratio considering both dose rate and dose has been established. Additionally, irradiation hardening effects induced by loops demonstrate that high dose rates increase the density of <111> dislocation loops and inhibit their movement, thereby significantly improving material hardening. This study not only validates the feasibility of neutron damage simulation using triple-beam irradiation but also provides critical experimental support for predicting long-term service behaviour of nuclear materials.