Atomic-scale Simulation Of Irradiation Damage In Tungsten

Nuclear fusion energy is one of the best energy for mankind,and as long as the controlled release of nuclear fusion energy can be achieved,humans can solve the energy problem once and for all.Therefore,the choice of nuclear fusion reactor materials is particularly important.The plasma-facing materials(PFMs)in nuclear fusion reactor are under the strong irradiation of high-energy neutrons.Therefore,irradiation damage is the main reason for their failure.After a long period of accumulation and evolution,the radiation induced-point defects can lead to changes in the macroscopic properties and the degradation of the mechanical properties of the material,and results in material failure.Due to the excellent performance of tungsten(W),it is considered to be the most promising candidate materials for PFMs and divertor materials in future nuclear fusion reactors.However,the grain boundary(GB)in W will interact with the radiation-induced point defects.Therefore,it is important to study the interaction mechanism between GBs and irradiation-induced defects,which has an important effect on clearly understanding the role of GBs,and regulating size and orientation of grain to improve the resistance property and performance of materials on radiation damage.Two atomic-scale simulation methods are used in this paper: the molecular dynamics method(MD)and the self-evolving atomistic kinetic Monte Carlo method(SEAKMC).MD was adjusted accordingly to the characteristics of irradiation damage,and then used the adjusted MD to study the interaction between GB and irradiation-induced point defects in W and to explore the influence of GB parameters on anti-radiation performance of materials.Besides,SEAKMC was used to study the dffusion-related issues of irradiation-induced point defects in W.The six symmetric tilt GBs of body-centered cubic W are taken as objectives and the energy of the primary knock-on atom(PKA),EPKA,is 3 and 5 keV,and the simulated temperature is 300 K in this paper.In the study of interaction between irradiation-induced point defects and GB,we designed the scheme of calculational simulation.The atomic evolution view of the interaction between GB and irradiation-induced point defects was given by visualization and quantitative analysis of the number of the point defects distribution.The results showed that the GB had a bias-absorption effect on interstitials compared with vacancies.It showed that the number of surviving vacancies was statistically increasing withthe increase of the distance between PKA and the center of the GB.While the number of interstitials didn't change much,and was less than the number of interstitials in the single crystal.The number of surviving vacancies in the grain interior(GI)was always larger than that of interstitials.During the collision cascades which include the ballistic stage,the recombination stage and the stable stage,the number of point defects increased first,then decreased and finally stabilized.The reduction of the number of point defects occured in the recombination stage,and there were two main mechanisms that worked together: vacancy recombined with interstitial and interstitial diffused towards the GB.The larger the ratio of the GB region overlapped with the peak defect area of the cascades(PDZ),the relatively smaller the number of surviving point defects in the grain interior;and when the two almost didn't overlap,with the distance from the GB increased,the number of vacancies generally increased first and then reduced.With the increase of EPKA,the vacancy-intensive area had a tendency to move forward(toward GB).The interstitial distribution was relatively uniform and was affected by the EPKA far less than the situation of vacancy.This phenomenon was a direct result that the GB had a bias-absorption effect on the interstitial.Through the simulation of the diffusion of point defects,we obtained that the diffusion constant of monovacancy and interstitial in W was 4.37×10-7m2/s and 1.07×10-7m2/s,respectively;and the migration energy was 1.45 eV and 0.015 eV,respectively.It can be seen that the migration energy of interstitial was very small and much smaller than that of monovacancy,which can be used to further understand the results of the interaction between GB and irradiation-induced point defects in W.In the study of the effect of GB parameters on anti-radiation performance of GB systems,it was found that in the six GB systems that were studied,the anti-radiation performance of materials had an increased trend with the increase of the the rotation angle ?.However,there was no obvious rule between the coincident site lattice parameter ?,the GB energy E and the anti-radiation performance of materials.In this paper,we study the evolutionary details of the interaction between the symmetric tilt GB and irradiation-induced point defects,which can help us to clearly understand the mechanism of the interaction between GB and irradiation-induced defects.The designed scheme of calculational simulations is completely applicable to the investigation of the interaction between other types of GBs and irradiation-induced point defects.