| The nuclear fusion energy is the most powerful energy in future. It is clean, safety, and inexhaustible. The realization of nuclear fusion reactors depends strongly on the developments of the high-performance materials in reactor component. Behind the Plasma-facing materials is the first wall structure materials, which can be used as the wall of the vacuum chamber and contain coolant, and can also be designed as the part of the cladding in the majority of reactor. These structure materials will be used in harsh environment, which means they will be suffered to high flux of neutron generated by nuclear fusion reaction; meanwhile a large number of transmutation products such as hydrogen and helium will go into the materials. So these materials should possess excellent properties which can resist to irradiation damage and serve at high temperature.Ti3SiC2exhibits the characteristics of ceramic materials, such as being resistant to high temperatureã€oxidation and corrosion, also possesses the characteristics of metal materials, like with good electrical and thermal conductivities, good machinability. Its cost is even lower than that of the SiCf/SiC composites for manufacturing. On the other hand, it has better connection properties. Because of its low activation performance, it is expected to be candidate material for fusion reactor structural materials. Using the first principle method, we investigated the effect of He impurities on the properties of layered Ti3SiC2. Helium usually segregates near Si planes. The evolution of He weakens the cohesion between Si-Ti layers, and intensifies delamination in a way of cleaving between Ti and Si layers. When a vacancy is introduced, we found that the vacancy prefers to trap two helium atoms forming a VHe2complex. With the accumulating of the complex in the Si layer, the complex will grow up into tabular cluster. The tabular He-V complexes may directly lead to crack nucleation on the cleavage plane of Ti3SiC2. As a consequence, the effect of He impurities concerning weakening the mechanical properties of Ti3SiC2has to be considered when such Ti3SiC2materials are chosen as high temperature structural materials.Reduced Activation Ferritic/Martensitic steels (RAFM) have a good resistance to high strength, corrosion and creep at high temperature, with low irradiation swelling and thermal expansion coefficient, also have better thermophysical properties. With so many excellent thermal physical and mechanical properties, they are expected to be the first choice as the structural materials for future fusion power reactors. Using the first principles based on density functional package in VASP, we simulated the nucleation of vacancy cluster in the presence of hydrogen atoms in bcc-Fe. The findings show that vacancies can easily trap hydrogen. H atoms prefer to stay surrounding the vacancy cluster and form strong Fe-H bonds with nearest neighbour Fe atoms, which induce the anisotropic nucleation of vacancy cluster, while not in3-dimensional shape. The nucleation is on plane{110} along<111> direction. This finally leads to micro-crack propagation, then affect the performance of the material. We give a possible explanation about hydrogen embrittlement mechanism.The innovation points of this paper are that:on the atomic scale, by simulating the behavior of helium in Ti3SiC2and the interaction of helium and vacancy, we predict that He induces the formation of micro-crack along Si layer, which will lead to brittleness of this materials. In bcc-Fe, we explained the anisotropic nucleation of vacancy cluster when the concentration of H is low, which has been observed in experiments. Although, on the atomic scale, the simulated results indicate the micro-crack in a-Fe was induced by the bonds of H-Fe by simulating the trivacancy grows in the presence of hydrogen. |
