Temperature effect on cavity evolution by triple-beam irradiation

To understand the synergistic effects of irradiation damage and transmuted helium and hydrogen in reduced-activation ferritic/martensitic (RAFM) steels irradiated by fusion neutrons, China low-activation martensitic (CLAM) steel was subjected to Fe+H+He triple-beam simultaneous irradiation under controlled conditions. The experiments were conducted at three temperatures of 350 °C, 450 °C and 550 °C, with irradiation doses of 11 dpa, 22 dpa and 33 dpa applied at each temperature, maintaining the He ratio of 11 appm/dpa and H ratio of 44 appm/dpa. At 350 °C, the increase in swelling was attributed to an increase in the number density of helium bubbles. At 450 °C, the helium bubble density saturated between 11 and 22 dpa, transitioning to cavities growing under bias-driven mechanisms, ultimately resulting in the formation of the largest voids. At 550 °C, the high temperature suppressed the number density of cavities, while thermal emission limited the void growth rate. With increasing doses, the size distribution gradually transitioned from unimodal to multimodal due to helium bubble-to-void transformation and the influence of size on growth rates, a phenomenon more pronounced at higher temperatures. At the three temperatures of 350 °C, 450 °C and 550 °C, CLAM steel experienced irradiation hardening, minimal changes, and irradiation softening, respectively, with hardness variations closely related to irradiation swelling. The results revealed the evolution of irradiation-induced defects and swelling under the synergistic effect among irradiation damage, helium and hydrogen.