The Properties Of The Li-Pb And Fe-Li Interfaces:Atomistic Simulations

Energy problem is one of the severest problems faced by the world,and developing the D-T fusion energy is thought to be the most promising way to solve this problem.Although the feasibility of developing the D-T fusion energy has been verified in theory,there are yet still many problems should be conquered in engineering to realize the commercial application of fusion energy,and material problem is the most important one.Blanket is a very important component in the future fusion reactors,which undertakes many significant functions,such as tritium breeding,heat transmission and irradiation resistance,so the development of the techniques relevant to blanket directly affects the development of fusion techniques.However,how to produce massive high quality LiPb eutectic,which is one of the candidates of liquid tritium breeder in the future fusion reactors,and to improve the compatibility between liquid tritium breeder/liquid first wall and the structure materials of the blanket are still challenging tasks encountered on the way to developing fusion techniques.This dissertation mainly focuses on that two problems,applying molecular dynamics simulation to carry out relevant works,we hope this work can provide some theoretical instructions for solving these problems in engineering.For this purpose,the elemental potentials for Li,Pb and Fe,and the alloy potentials for Li-Pb and Fe-Li systems were constructed,and then the reliability of these potentials was tested.The testing results indicate these potentials can well reproduce the tested physical quantities.Based on these potentials,the alloying of the Li-Pb interface at different temperatures was studied,the alloying process and alloying product were detailedly analyzed.The results show that three main stages—interface disordering stage,ordered phase nucleation stage and ordered phase growth stage are included in the alloying process at all temperatures.The ordered phase formed at the interfaces is B2-LiPb intermetallic in all cases,the B2-LiPb is stable and acts as a diffusion barrier impeding the alloying process of the Li and Pb atoms on the two sides of the interface.In addition,this study also manifests that different temperatures influence the uniformity of the produced LiPb eutectic by impacting the mutual diffusion speed of Li and Pb atoms as well as the nucleation time of the B2-LiPb.And then we investigated some properties of the Fe-Li so lid-liquid interfaces,our findings indicate that the interfacial properties show remarkable anisotropy and temperature dependence.For the Fe(001)-Li and Fe(110)-Li solid-liquid interfaces,the liquid Li near the interfaces presents distinct layering phenomenon along the interface normal at relatively low temperatures,and these layers do exhibit the same symmetry of the Fe crystal plane contacting with the liquid Li.Although we also observed the layering phenomenon of the liquid Li near the Fe(111)-Li solid-liquid interface at 500K,these liquid Li layers disappeared more quickly than those near the other two interfaces as temperature increases.What's more,the degree of in-plane order of liquid Li near the Fe(111)-Li solid-liquid interface is much lower than that in the other two cases at the same temperature.As for the diffusibility of the Li atoms near the interfaces,the nearer the Li atoms to the interfaces,the slower the Li atoms diffuse,nevertheless the Li atoms near the Fe(111)-Li solid-liquid interface diffuse a little faster than those near the other two interfaces.As to the compatibility,the compatibility between solid Fe and liquid Li is worse in the case of the Fe(111)-Li solid-liquid interface,because it is much easier for Li atoms diffusing into the Fe block in this case.Deep analysis reveals that the anisotropy of the interfacial properties is closely related to the different stability of the Fe atoms near the three interfaces.For these three interfaces,temperature imposes a similar effect on their properties,as temperature increases,the degree of order of the liquid Li near the interfaces decreases gradually,while its diffusibility increases,and the compatibility between solid Fe and liquid Li degrades.Besides,we investigated the clustering behavior of Fe atoms in liquid Li and the effect from Fe clusters on the viscosity of liquid Li.The results indicate that the Fe atoms dissolved in liquid Li will aggregate to form clusters gradually,and the higher the temperature,the faster the clustering process.Interestingly,the formed Fe clusters resulted in an augment of the viscosity of liquid Li,and we found that the larger the Fe clusters,the larger the increment.At last,the responses of the Fe(001)-Li solid-liquid interface and the Fe(001)surface under the irradiation of a Fe atom with 20keV energy were comparatively researched.Analysis suggests that the evolution processes of the interface and surface structure as well as the evolution processes of the defects in the Fe blocks are very similar.The irradiation regions all suffered an evident damage in the interface and surface cases,where a certain number of Fe atoms were sputtered out,and then a crater-shaped pit surrounded with a "ridge" formed there.In these two cases,the retention rate of the irradiation defects is very low after the Fe blocks experienced a sufficient relaxation,irradiation did not have cause a plenty of Li atoms diffusing into the Fe block under the interface situation.The existence of liquid Li is beneficial for the sputtered Fe atoms' clustering,and a 4.13 to 8.95 A thick liquid Li layer can partly weaken the damage,caused by the high energy Fe atom after passing through the liquid Li layer,to the Fe block.