Ion Irradiation Damage Of New Reduced Activation Martensitic Steels

Ion irradiation was used to simulated neutron irradiation effects on the reduced activation ferric/martensitic steels. The reduced activation ferric/martensitic steels are proposed as primary structural materials of international tokamak experimental reactor and projected fusion power plants. Super-clean reduced-activation martensitic steels (namely SCRAM steel, supplied by Huazhong University of Science and Technology) was used in the present study. The SCRAM steel, where Ti was used to replace Ta, was melted by vacuum induction melting and electro-slag remelting (ESR) at argon atmosphere.1. Two SCRAM steels with different Ti concentrations were irradiated with Fe+(5dpa,40dpa and50dpa) at elevated temperatures and then inverstigated with transmission electron microscopy. The carbides were coarsened with the irradiation dose increasing and the coarsening in the high-Ti SCRAM steel was smaller. Small size precipitates were induced by high irradiaton dose. They were smaller and mainly (V, Ti)(C, N) precipitations in the high-Ti SCRAM steel. After irradited with40dpa Fe+15appm He/dpa+60appm H/dpa, the tensile strength of SCRAM steel increased while impact energy decreased. Irradiation induced hardening was more severe in the low-Ti SCRAM steel. The enrichment of Cr, depletion of Fe, and the coarsening of carbides were more severe in the low Ti-concentration SCRAM steel and it would induced extra hardening. The addition of Ti lead to the formation of MX precipitates and the microstucture of high-Ti SCRAM steel were more stable during irradiation.2. The SCRAM steels were irradiated with single-beam (40dpa Fe+) and sequential-beams (40dpa Fe+15appm He/dpa) at350?and55O?and then inverstigated with transmission electron microscopy. The size of bubbles and swelling were larger while small size precipitates grew up under sequential-beam irradiations, compared to single-beam irradiations. The largest size of cavities was observed after sequential-beam irradiation at550?. The coarsening of carbides, the segregation of Cr and W and depletion of Fe in carbides were observed, and the maximum depletion of Fe and enrichment of Cr occurred under irradiation at350?.3. In order to investigate the synergistic effect of helium and hydrogen on swelling in reduced-activation ferritic/martensitic steel, SCRAM steels were irradiated with by single-beam (He+) and sequential-beams (He+and H+) at different temperatures from250?to650?. Transmission electron microscope observation showed that implantation of hydrogen into the specimens pre-irradiated by helium can result in obvious enhancement of bubble size and swelling rate which can be regarded as a consequence of hydrogen being trapped by helium bubbles. Due to the migration and combination of bubbles, bubble size and swelling rate increased with the inctreasing of temperature and were maximizing at450s?. When temperature was high enough, say above450?, point defects would become mobile and annihilate at dislocations or surface. As a consequence, helium could no longer effectively diffuse and clustering in materials and bubble formation was suppressed. When temperature was above500?, helium bubbles would become unstable and decompose or migrate out of surface. Finally no bubble was observed at650?.Then, single-beam (He+or H+) and sequential-beam (He+/H+or H+/He+) irradiation on SCRAM steels at450?was carried out to investigate helium/hydrogen synergistic effects on the microstructure of reduced-activation martensitic steels. Helium bubbles were observed after helium implantation, and the density was very low, while no void was observed after hydrogen implantation. In the He+/H+sequential-beam irradiation, the number density of bubbles increased rapidly at low hydrogen dose, and then the average size of bubbles increased at higher hydrogen dose. Helium bubbles were also found in the H+/He+sequential-beam irradiated specimen but its swelling was smaller than that in He+/H+sequential conditions. It was concluded that the effect of hydrogen atom on the nucleation and growth of bubbles may support to enhance the diffusion of Helium atoms/He-vacancy clusters and the hydrogen irradiation after the helium one can increase on the nucleation and growth of helium bubbles, while helium bubbles may enhance the retention of hydrogen atoms to form He-H-vacancy complexes.