| Zirconium alloys are not only excellent cladding materials for nuclear fuel,but also good as hydrogen storage materials.The production of nuclear energy and hydrogen storage are closely related to zirconium alloys.The zirconium alloys are easily brittled by hydrogen in the service as a shell material,which cause enormous losses,scientists have focused on solving the problem of hydrogen embrittlement for a long time.Further study of the interaction between hydrogen and zirconium has important value in solving hydrogen embrittlement and develop hydrogen storage materials.In the present work,the crystal structures,energy properties,atomic diffusion characteristics,elastic moduli and mechanical properties of Zr-H system were investigated systematically using first-principles.This work also explained for these properties from electronic level and studied the mechanism of hydrogen and zirconium from micro.Determintion of the Zr-H crystal structure is the basis of the calculation of all properties.So firstly we researched the occupation of hydrogen in Zr-H system.The results showed that the lattice distortion and volume expansion of both ?-Zr-H and ?-Zr-H crystals with hydrogen atoms at the octahedral sites were lower than the ones with hydrogen atoms at the tetrahedral sites.However,the dissolution heat of the hydrogen atom in the tetrahedral sites were less than that of the octahedral sites.Therefore,the hydrogen tended to occupy the tetrahedral sites.Electronic structural analysis found that the influence of hydrogen atoms was localized,it changed the state density of neighboring zirconium atoms.There was a charge transfer from 4p orbit of ?-Zr atoms and 4d orbit of ?-Zr atoms which were the nearest neighbors of hydrogen to 1s orbit of hydrogen atom,reduced the ?-Zr atoms bonding strength and enhanced the ?-Zr atoms bonding strength.The study of the diffusion behavior of hydrogen atoms in Zr-H system showed that: hydrogen diffusion in ?-Zr was anisotropy and the calculated diffusion activation energy of hydrogen diffusion in the basal plane was smaller than along c axis,and the calculated activation energy were in agreement with the experimental data.Hydrogen diffused along the T-T path on the base surface,along the T-O-T path between two different atomic layers.In ?-Zr,the direct T-T mechanism was most favorable for hydrogen diffusion,needed to go through the middle octahedral space when diffused between the next nearest neighbor tetrahedral sites.The research on the self-diffusion behavior of zirconium was discovered based on the vacancy diffusion mechanism.The addition of hydrogen atoms reduced the single vacancy formation energy and the activation energy for zirconium diffusion in ?-Zr,which promoted the self-diffusion of zirconium atoms.The addition of hydrogen atoms improved the single vacancy formation energy but reduced the activation energy for zirconium diffusion in ?-Zr,which hindered the formation of vacancy when promoted the self-diffusion of zirconium atoms.The surface energy,elastic modulus,tensile and compressional mechanical properties of zirconium-hydrogen system were simulated.The study of surface energy showed that hydrogen reduced the surface energy of ?-Zr basal plane and prismatic plane,which increased surface stability,but reduced the surface energy of ?-Zr {100} and {110} plane.The elastic modulus and stress-strain curves of Zr-H system were calculated.The results showed that hydrogen reduced Young's,shear and bulk modulus of ?-Zr,also reduced the index of plastic G/B,which increased its plasticity.One more,hydrogen reduced ?-Zr's theoretical tensile and compressive strength along c,which reflected the weak bond effect of hydrogen.In ?-Zr,Young's,shear and bulk modulus,G/B were reduced by hydrogen,hydrogen improved the mechanical stability of ?-zr and improved ?-Zr's theoretical tensile strength,increased its ability to resist compression,which reflected the strong bond effect of hydrogen. |
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