The Behavior Of Hydrogen And Helium In Heterogeneous Interfaces

The hydrogen and helium bubbles in materials usually leads to the embrittlement of the materials,which threaten the safety and stability nuclear facilities.Due to the physical and chemical properties are quite different at two sidesof the interface,the interface has always been regarded as the source of corrosion and fracture.More importantly,the interface of the composite material would trap the hydrogen and helium atoms and then resulting the formation of stable bubbles,which are a large potential threaten for spallation neutron sources and Boron Neutron Capture Therapy equipment(BNCT).We utilized the first principles calculation method to study the hydrogen and helium behaviors of the spallation neutron source tungsten/tantalum composite target and BNCT lithium/tantalum composite target.In addition,the capture of hydrogen and helium atoms in the interface has the beneficial aspect.Recently,a large number of studies have shown that Nano-multilayer composites containing high-density interfaces can inhibit the nucleation and growth of bubbles in the material to a certain extent,so the interface control(Changing the composition,atomic structure,and interface density of adjacent atomic layers)to improve the material's resistance to radiation and blistering has become one of the important R&D strategies for new nuclear power materials.Therefore,this study also combined the neutron reflection technology and the First principles calculation method to systematically study the bubble formation behavior of helium atoms in the W/Ni interface region.The main research contents and results of this paper are as follows:(1)The dynamic behaviors of hydrogen atoms at the Li/Ta interface was studied through the first-principles calculation method.Based on the bulk parameters and surface energies of Li and Ta,Li(100)/Ta(100)and Li(110)/Ta(110)interfaces were constructed.Based on the interface models,the dissolution,migration and blistering behaviors of hydrogen atoms around the Li(100)/Ta(100)and Li(110)/Ta(110)interfaces were studied.the results show that the dissolution energy of hydrogen atoms in the Li/Ta interface is significantly lower than those in Li and Ta layers.This is because the hydrogen dissolution energy is closely related to the electron density in the environment.With the increasing electron densisy,the dissolution energy of hydrogen atom shows a decreasing trend first,when the electron density reachs a critical value,the dissolution enegy begins to increasing with the increasing electron densisy.The critical electron density is just in the Li/Ta interface,so the dissolution energy of hydrogen atoms in the Li/Ta interface is the lowest.At the same time,the energy barrier for hydrogen atoms to migrate from the Li and Ta layers to the Li/Ta interface is very amsll,which means that the Li/Ta interface has a certain capacity to contain hydrogen atoms and may form a hydrogen-rich layer at the interface.Subsequent calculation results on the average hydrogen trapping energy show that the average hydrogen atom trapping energy of hydrogen atoms in Ta layer is significantly lower than that in Li layer,which means that hydrogen atoms will be more easily binding into hydrogen bubbles in Ta layer.(2)The dynamic behaviors of H and He atoms at the W/X(X=V,Cr,Nb,Mo,Ta)interfaces were sdudied through the first-principles calculation method.Based on the bulk parameters and surface energies of W,V,Cr,Nb,Mo and Ta,W(110)/X(110)(X=V,Cr,Nb,Mo,Ta)interfaces were constructed.Based on the interface models,the dissolution and migration behaviors of hydrogen and helium atoms around the W(110)/X(110)(X=V,Cr,Nb,Mo,Ta)interfaces were studied.At last,the temperature effect on the stability of hydrogen and helium atoms were studied through the Ab Initio Molecular Dynamics(AIMD).The results show that whether it is a hydrogen atom or a helium atom,its dissolution energy is positively correlated with the electron density in the surrounding environment.The dissolution energy of hydrogen and helium atoms in W layer is significantly higher than that in the other side or the interface,and the dissolution energy in the interface is between the two sides,which is consistent for all W/V,W/C,W/Nb,W/Mo and W/Ta interfaces.In addition,due to the presence of inernal stress,the lattice binding of impurity atoms near the interface will be weakened,so its migration ability will be enhanced to a certain extent.Therefore,the energy barrier for hydrogen and helium atoms to migrate across the interface from W to Ta is relatively low,especially for helium atoms.At a temperature of 1000 K,helium atoms can spontaneously migrate from the W/Ta interface to Ta.(3)Combined with neutron reflection experiment and theoretical simulation,the dynamic behavior of He atom at W/Ni interface was studied.The W(30 nm)/Ni(30nm)double-layer film samples were prepared by magnetron sputtering.On this basis,the structural changes of the film samples and the behavior of helium atoms in the film were studied.It's found that He atoms will preferentially gathering in the W/Ni interface and form an enriched layer after He~+irradiation.When helium atoms in the interface are nearly saturated,helium atoms begin to accumulate in the W and Ni layers.Theoretical simulation results show that helium atoms preferentially gathering in the W/Ni interface is due to the lower vacancy formation energy near the interface and the larger binding energy between the vacancy at the interface and the helium atom.On the other hand,experimental research found that a large number of helium atoms migrated from the tungsten layer to the W/Ni interface,wihich may originated from the large dissolution energy of helium atoms in the W layer,compared with thos of the interface or Ni layer.This paper systematically studied the behavior mechanism of H and He atoms at various heterogeneous interfaces and evaluated the behavior of hydrogen and helium in the composite target of spallation neutron source and BNCT from a physical point of view,which provided a theoretical references for neutron target design and upgrade.In addition,the extensive research on the migration and foaming behavior of H and He atoms in the BCC/BCC and BCC/FCC interfaces are helpful for understanding the H and He atoms behavior law in the heterogeneous interfaces.We hope the study would establish a broad and comprehensive understanding,thereby promoting the design and development of high-temperature resistant photographic and anti-foaming Nano multilayer film composite materials.