Search

Based on the experiment and first-principles calculation methods, the evolution of microstructure, mechanical properties and electrical conductivity of low-carbon steel were investigated at various annealing conditions. The results show that with the increase of annealing temperature, the morphology of ferrite matrix grain undergoes a transformation from narrow and long fibrous to, accompanied by the continuous growth in size. The strength of α-fibre texture is reduced continuously while the strength of γ-fibre texture increases evidently. The tensile and conductivity testing results indicate that with the increase of annealing temperature, both the yield strength and tensile strength of the steel decrease, while the elongation exhibits an opposite tendency due to the continuous growth of ferrite grains and dissolution of tertiary cementites. Additionally, the electrical conductivity increases because the reduction in the number of grain boundaries weakens their scattering ability to electronic waves. The first-principles calculation results indicate that with increasing distance to the interface, the segregation energy of Nb atom in ferrite matrix is reduced, as well as the interfacial energy of the structure is also decreased. The interface segregation preference of Nb atoms induces the transfer of charge, which is beneficial to enhance the conductivity of the ferrite matrix.

Radioisotope thermophotovoltaic (RTPV) generator has wide application prospects in sea, land, air, medical, electronics, and other fields. In order to better investigate the influence of alpha rays on emitters, thermophotovoltaic (TPV) cells, and other components, it is vital to find out a suitable way which can rapidly evaluate and select each of the components in TPV cells by the combination of heating and irradiation of alpha beam. In this work, a TPV cells test system, in which the tungsten emitter has been heated by the He+ ion beam experiment, has been investigated systematically. It is found that the Gaussian distribution of temperature in tungsten emitter is obtained along the radial direction under uniform distribution of He+ ion beam. The distance between emitter and TPV cells has a great effect on the radiant heat flux and temperature. The simulation results show that the TPV cells have the highest output power (~1.8 W) when the optimal distance between emitter and TPV cells is 80 mm. Moreover, as one of the prospective candidate emitters, the thermal stress of silicon carbide (SiC) emitter has also been evaluated under 400-W beam. It is feasible for He+ ion beam to rapidly evaluate and select each of components in TPV cell experiment. The work will accumulate important experience for the TPV cells test of higher electric output power and the design of RTPV generator.

Beryllium has been one promising candidate material for the neutron multiplication in the nuclear fusion reactor. A systematic study has been performed to get insight into the oxidation mechanism in the beryllium {101̅1} grain boundary. It has been found that the diffusion of an O atom from the bulk to grain boundary is much easier than that in the bulk and the grain boundary plane. Furthermore, multiple O atoms may segregate in the grain boundary due to the strong attraction of grain boundary. The O atoms segregated in the grain boundary could interact with the nearby Be atoms with the formation of beryllium oxide, which could be confirmed by the calculation of bond length, charge density difference, and Bader charge. Meanwhile, the pre-existing O atoms could induce the segregation of H atoms. The segregated H atoms could also interact with Be atoms, and beryllium hydride will be formed. The formation of beryllium oxide and beryllium hydride could induce the degradation of strength of Be. The present work could provide a more intensive understanding for the oxidation behavior in the Be grain boundary, which has been experimentally observed when exposed to the extreme environment.