| Energy and environment are the significant concerns in today’s society. The fusion reactor as a representative of advanced nuclear reactors is expected to provide long-term clean energy to the society. The key to the successful achievement of nuclear power technology depends on the material behavior under intense neutron irradiation. The structural materials of the fusion reactor endure the irradiation from energetic neutrons and He ions, resulting in serious damage in the structure materials. Therefore development of advanced materials with high resistance to irradiation and with high strength is the key to the successful setup of a prototype fusion reactor.Oxide dispersion strengthened(ODS) ferritic steels are fabricated though mechanical alloying and hot pressing/extrusion procedures. Oxide particles with a high density were embedded in the ferritic substrate so that a higher creep strength is achieved. ODS ferritic steels have better high-temperature creep rupture strength and higher irradiation resistance than conventional ferrictic steels, and show high prominence of application in advance nuclear reactors. Compared with neutrons, heavy ions can produce displacement damage and inject inert-gas impurities at a much higher rate in the candidate material. Nowadays, high-energy heavy-ion irradiation has been used as a useful method to study the irradiation characters of the candidate materials. Due to the very limited irradiation volume in heavy-ion accelerators and neutron sources(for instance, the IFMIF and D-Be small neutron source), the small specimen test technology(SSTT) is developed to study the mechanical properties of the materials. In the present work, thickness effect of the small punch test technology was studied. A FEM analysis was used to understand the fracture behavior in the small punch test, and was verified by a microscopic investigation of the fractured areas. The research and results are summarized as follows:(1) Small punch test have been carried out on the mechanical properties of Fe-22%Cr small specimens with four kinds of thickness at room temperature. The specimens fracture morphology though small punch test was observed by scanning electron microscopy. Experimental results showed that the maximum load and yield load increase with the thickness of the samples. A linear relationship with the thickness is proposed. Fracture surface displays typical ductile morphology, with a lot of dimples on the fracture surface. The outer surface of the hemispherical bulk part punched off is full of little bowings around which there were many microcracks caused by the stretch stress. The fracture crack depth and fracture energy increased with thickness of the samples. The fracture did not occur in the center position of the fracture. The fracture position estimated by the finite element model was in agreement with the experimental observation.(2) A commercial ODS ferritic steel MA956 were irradiated with high-energy 20Ne-ions at a terminal of the Sector-focused Cyclotron(SFC) at HIRFL(Heavy-ion Research Facility in Lanzhou). With the energy gradient degrader of the irradiation chamber, the primary energy(123.4 Me V) of the Ne-ion was dispersed into 30 different energies between 38.5-121.0 Me V, which resulted in a plateau distribution of lattice damage in the specimens. Specimens were irradiated from both sides so that the whole 60 um thickness was nearly uniformly damaged. The specimen temperature was maintained around 440 oC during irradiation. The irradiation dose was about 9?1016 ions/cm2, correponding to a damage level of 0.7 dpa and Ne concentration of 350 appm. The specimens before and after irradiation were tested with the small-ball punch technique at room temperature and 500 oC, and the fracture morphology was observed by scanning electron microscope. The results show that MA956 underwent significant ductility loss, decrease of fracture toughness after the irradiation with high-energy 20Ne-ions. |
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