Molecular Dynamics Simulation Of The Radiation Resistance Of Ni-Fe And Ni-Co Alloys

The scarcity of energy prompts people to develop nuclear energy,so that nuclear reactors are continuously upgraded,and the high radiation resistance of nuclear materials is required.It has been proved that the single-phase solid solution alloys have many outstanding properties,such as good thermal stability,high mechanical properties,and good corrosion resistance.In this work,LAMMPS code based on the molecular dynamics method is employed to simulate displacement cascades in Ni-Fe alloys and Ni-Co alloys and thus to investigate the radiation damage resistance.The main works and conclusions are as follows:1.We simulated the cascade events in pure Ni and Ni-xFe alloys(x = 20,25,30,50,60)under three different PKA energies by using EAM potential.By compared with the number of stable Frenkel pairs in pure Ni and Ni-Fe alloys,we found that with the increasing of Fe concentrations,the number of Frenkel pairs significantly decrease in Ni-Fe alloys,especially the Fe concentration is 25-30%.Then the decrease tendency will be markedly slows,which indicates that the alloying with 25%-30% Fe in Ni reduces rapidly the primary defect production and Ni-xFe(x =25%-30%)alloys may effectively resist irradiation damage.Moreover,the difference of stable Frenkel pairs numbers in Ni-Fe alloys produced by three PKA energies is smaller than pure Ni,which means that Ni-Fe alloys have higher stability in an irradiation environment than pure Ni.2.The sizes of defect clusters and distributions of large defect clusters in pure Ni and Ni-Fe alloys are analyzed,and we found that with the increasing of Fe concentrations in Ni-Fe alloys,the average size of interstitial clusters and vacancy clusters decrease.It is of interest to note that the ratio of vacancies contributed by Fe is only slightly lower than the concentration of Fe in the Ni-xFe alloy,but such concentration dependence is not found in interstitials.3.The cascade collision of pure Ni and Ni-xCo alloys(x =20,25,30,50,60)under three different PKA energies were simulated by MD method using MEAM potential.By comparing the number of stable Frenkel pairs in pure Ni and Ni-Co alloys,we found that when PKA energy is low,such as 10 keV,the addition of Co does not significantly improve the resistance of irradiation.But when the PKA energy is high,with the increasing of Co,the stable Frenkel pairs in Ni-Co alloys significant decrease,which indicates that the Ni-50 Co alloy may have the best resistance of radiation in Ni-xCo alloys.4.The simulation results of cascades in pure Ni show that the number of the stable Frenkel pair obtained by MEAM potential is slightly lower than EAM potential.This may be due to that the MEAM potential is an extension to the original EAM potential which adds angular forces,so it's harder than the EAM potential.However,when the PKA energy is higher than 25 keV,the effect of potentials becomes smaller.5.The comparison of the defect composition in Ni-Fe alloys and Ni-Co alloys shows that the species of SP-CSAs elements do affect the radiation resistance of alloys.The decrease of stable Frenkel pairs in Ni-Fe alloys is faster than that in Ni-Co alloys with the same PKA energy,which means Ni-Fe alloys may have higher radiation resistance than Ni-Co alloys.At the same time,due to the unique chemical order in alloys,the formation energy and migration energy of defects are also different,the proportion of defects contributed by Co in Ni-Co alloy is higher than that of Fe in Ni-Fe alloy.