| Lead-bismuth eutectic alloy has become the main candidate coolant for lead-cooled fast reactor and high-energy neutron source candidate spallation target because of its low melting point,high boiling point,excellent thermal conductivity,chemical inertia and good neutron characteristics.However,under high temperature environment,liquid lead-bismuth has a strong corrosion effect on the matrix structural materials.The elements in steel will be dissolved in liquid lead-bismuth with different solubility(when the temperature is 1100 K,the solubility of Fe,Ni and Cr is 10-2 wt.%,10 wt.%and 10-2 wt.%,respectively).In order to understand the corrosion of iron-based materials caused by liquid lead bismuth,the corrosion behavior of iron-based materials in high temperature liquid lead bismuth was studied in this paper.In the working environment,a large number of defects（such as vacancies,dislocations and voids）are introduced into structural materials by the irradiation of high-energy protons and neutrons,which poses a great threat to the service life and safety of materials and increases many unstable factors.Liquid lead-bismuth has a great influence on the corrosion behavior of structural materials with defects.It is particularly important to explore the mechanism and apply it to practical applications.Therefore,this paper uses molecular dynamics to study the dissolution and corrosion behavior and mechanism of defective iron crystals and iron-nickel alloy materials in high-temperature liquid lead-bismuth.The main research content is divided into the following three parts:（1）In this part,the molecular dynamics method was used to simulate the corrosion behavior of iron crystals containing vacancies in high temperature liquid lead bismuth.The vacancy concentrations of iron crystals were:0.2 at.%,0.4 at.%,1.0 at.%and 2.0 at.%,respectively.Each vacancy concentration system was simulated at 700 K,823 K,873 K,973 K and 1073K,respectively.The adsorption energy of Pb and Bi atoms on the surface and the pair distribution function between atoms are calculated to verify the accuracy and correctness of the potential function used in this paper.The penetration path,depth and number of Pb and Bi atoms in the matrix were analyzed in detail.It was found that the penetration depth and number of Bi atoms were more significant than those of Pb atoms.The substitution energy of vacancies and Fe atoms inside and on the surface of the iron crystal is replaced by Pb/Bi,and the substitution energy at the surface is smaller,so the vacancies and Fe atoms on the surface are easier to be replaced.（2）In this part,four dislocations with different densities are pre-set in iron-based materials.The simulated temperatures are 823 K,873 K,973 K,1073 K and 1173 K.The four dislocation density systems are simulated at these five temperature scales.Through molecular dynamics simulation,the evolution process of dislocation in the corrosion process was analyzed,and the substitution energy and dislocation strength of Pb,Bi atoms and Fe atoms near the dislocation were calculated.Because the substitution energy of Pb/Bi for Fe atoms at the dislocation line is lower,Pb and Bi atoms are more inclined to infiltrate along the dislocation line,which further demonstrates the corrosion phenomenon and deep corrosion mechanism.（3）In this part,the corrosion of iron-nickel alloy by liquid lead-bismuth was simulated,in which the content of Ni was 0 at.%,10 at.%,20 at.%,30 at.%and 45 at.%,and the simulation temperature range was 823～1173 K.In the simulation process,the variation trend of the dissolved amount of Fe and Ni atoms in the polycrystalline matrix,the depth of Pb and Bi atoms penetrating into the matrix and the evolution of their position distribution,as well as the microscopic mechanisms such as the change of atomic structure and dislocation evolution in the matrix were observed and analyzed.Through the substitution energy of Pb and Bi atoms on the surface matrix atoms,it is known that Bi atoms are more likely to corrode the matrix atoms,and the binding energy of the matrix atoms inside the matrix shows that Bi atoms tend to combine with Ni atoms,and observing the distribution of atoms inside the matrix after corrosion,it is known that Pb and Bi atoms corrode more seriously at grain boundaries.In this paper,the corrosion behavior of iron matrix materials in liquid lead-bismuth was studied by molecular dynamics method.Combined with a variety of post-processing methods（such as python coding to extract data,the software of OVITO to analyze the corrosion behavior process,etc.）,the corrosion behavior and mechanism of iron matrix materials containing defects in high temperature liquid lead-bismuth have a deeper understanding and understanding,which refines the research in this direction and expands new perspectives and ideas. |
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