TEM Study Of Irradiation Damage In Reduced Activation Steels And Tungsten

The reduced activation martensitic steels are the prime candidate structural materials for projected fusion power plants, and tungsten is the prime candidate plasma facing materials. In fusion conditions, reduced activation martensitic steels will suffer the irradiation from the helium, hydrogen and other isotope gas atom generated by (n, a) and (n, p) nuclear transmutation reactions, and tungsten will suffer D-T plasma and helium irradiation. Transmission electron microscopy (TEM) was used to investigate hydrogen and helium ion irradiation effects on the reduced activation martensitic steels and tungsten in our paper.1. Dislocation loops in reduced activation martensitic steels induced by helium irradiation were investigated systematically. So far most studies concerning the effect of helium on microstructure in reduced activation martensitic steels were focused on helium bubbles and swelling, whilst few were reported to investigate the dislocation structures induced from energetic helium particles. Large dislocation loops were found in reduced activation martensitic steels after helium irradiation, and the size of these loops is much larger than that induced by other irradiation such as neutron, proton and heavy ion irradiation at the same dose. The mechanism might be as follows: helium atoms were easily trapped by the vacancies and then form He-V clusters, more self-interstitial atoms (SIAs) could be created, leading to the formation of large dislocation loops. And the size, number density and the burger vector of dislocation loops will vary with the irradiation temperature and irradiation dose. We also found that there exit a critical temperature and dose, the type of dislocation loops would change if approaching this critical value.2. The synergistic effect on the dislocation loops was investigated by changing the order of ion irradiation, i.e. helium ion, hydrogen ion, He/H sequential ion and H/He sequential ion irradiation at 450?. Compared with single-ion (He or H), the mean size of dislocation loops induced by sequential-ion irradiation were much larger. And the dislocation loops induced by He/H sequential-ion irradiation were the largest at the same dose. It suggest that hydrogen and helium play different role in the synergistic effect. Helium atoms were easily trapped by the vacancies to form He-V clusters, and then form He-H-V cluster by trapping hydrogen atoms. Large He-H-V complexes could trap SIAs around them and act as nucleation sites for I-loops through loop punching mechanism. As a result, SIAs or I-loops become larger by absorbing the excess ejected interstitial atoms.3. The nucleation and growth of the helium bubbles in tungsten was investigated under different irradiation temperature and dose. It is found that the nucleation of helium bubbles will be suppressed at low temperature, no bubbles could be found at 350?. When irradiated at 500?, helium bubbles could grow through "loop punching" mechanism. Higher temperature will promote the growth of the helium bubbles, the mean size of the helium bubble will increased with the temperature, while the density will decrease rapidly. When irradiated at 800?, the mean size of helium bubbles will increase with the irradiation temperature, while the density will decrease at first and then increase.4. The nucleation and growth of the hydrogen bubbles in tungsten was studied under different irradiation temperature and dose. We found that dislocation loops after irradiated at room temperature, several bubbles appeared and the dislocation loops disappeared when irradiated at 350?. The mean size of hydrogen bubbles will increase with the temperature when irradiated at higher temperature, and the density will increase at first and then decrease. When irradiated at 500?, hydrogen bubbles could grow through "loop punching" mechanism. Hydrogen bubbles will become unstable of move to the surface, thus the density will decrease rapidly when irradiated at 800?. When irradiated at 600?, the mean size of hydrogen bubbles will increase rapidly at first and then increase slowly with the irradiation temperature, while the density will be almost constant and then increase rapidly. Bubbles grew larger with increasing hydrogen irradiation fluence for small H-V clusters got more chance to coalesce to larger bubbles, thus bubble density almost remained unchanged. But when irradiated fluence increased to 2.25×1021/m2, and bubbles grown denser but not larger, because they stopped growing upwhen bubbles'size increasing caused their internal pressure decreasing.5. The synergistic effect on swelling in tungsten was investigated by changing the order of ion irradiation and irradiation temperature. It is found compared with single-ion (He or H), the density of bubbles induced by sequential-ion He/H irradiation were much larger. When irradiated at 500 ? and 800 ?, the mean size of bubbles induced by He/H sequential-ion irradiation was larger than single helium or hydrogen irradiation; while when irradiated at 600 ?, the mean size of the bubbles induced by He/H sequential-ion irradiation was a little larger than single helium irradiation.