Simulation Study Of Oxidation And Dissolution Corrosion Of Iron-based Alloys In Lead-Cooled Fast Reactors

Low activation ferrite/martensite steel(RAFM steel)is considered as the first choice of structural materials in lead-cooled fast reactor(LFR)because of its good thermal conductivity,low expansion coefficient and good radiation resistance.In the service environment of LFR,structural materials not only face high temperatures and strong radiation,but also are exposed to highly corrosive liquid lead or lead bismuth eutectic(LBE)coolants.Experimental research has found that the irradiation damage caused by high-energy neutrons in LFR not only promotes the solution corrosion and embrittlement of structural materials in liquid metals,but also intensifies the oxidation corrosion of structural materials,and even causes the destruction of the oxidation layer.Further research has shown that adding an appropriate amount of alloying elements to Fe-based structural materials can slow down the oxidation corrosion of the materials.Therefore,studying the corrosion behavior of structural materials in liquid LBE is of great significance for revealing their degradation mechanism in liquid metal environments.At the same time,this can also provide a mechanism reference for the subsequent development of corrosion-resistant materials.This article mainly starts with the oxidation corrosion and solution corrosion of Fe-based structural materials in liquid lead,and uses first-principles calculations and molecular dynamics simulations to study the corrosion behavior of structural materials.The main research content and results of this article are as follows:Firstly,using first-principles calculations,we investigated the influence of alloying elements(Si,Cr,Mo)on the evolution behavior of oxygen(O)atoms in Fe grain boundaries.Research has found that Si,Cr and Mo tend to segregate to grain boundaries and affect the solution and diffusion of O atoms at Fe grain boundaries.These effects are closely related to the interaction between alloying atoms and O atoms,and are determined by the distortion of local atomic structure and the competition between electronic interactions.By using the Langmuir-McLean model,a preliminary investigation was conducted on the variation of oxygen concentration in the grain boundary region with the matrix/environmental oxygen concentration.The effect of alloying elements on the distribution of oxygen concentration near the grain boundary was investigated by incorporating the segregation energy of O atoms in the grain boundary of the alloy into the model.Research has shown that the higher the oxygen concentration in the matrix,the higher the oxygen concentration in the grain boundary region;the stronger the ability of grain boundaries to capture O atoms,the higher the oxygen concentration at the grain boundaries;the alloying element Cr,which is biased towards the Fe grain boundary,promotes the accumulation of O in the Fe grain boundary,while Si and Mo reduce the oxygen concentration.This work not only reveals the influence of alloying elements on the formation of grain boundary oxides,but also provides intuitive estimates of oxygen concentration in grain boundary regions under different environments.Secondly,based on molecular dynamics methods,we simulated the interaction process of atoms at the Fe-Pb solid-liquid interface under different service environments.Studying the dissolution corrosion of Fe atoms at the solid-liquid interface and the permeation characteristics of Pb atoms,which are related to the microstructure at the interface.By comparing the interaction characteristics at the solidliquid interface at different temperatures and times,it was found that both the increase in corrosion temperature and time exacerbate the dissolution corrosion of liquid Pb on the Fe surface.This result preliminarily reveals the microscopic process and influencing factors of dissolution corrosion of Fe-based structural materials in liquid metals.Based on the above research results,we preliminarily obtained the energetics and dynamics characteristics of the interaction between the alloying and O atoms at the grain boundary of the Fe-based alloy and the microscopic process of the interaction between the atoms at the Fe-Pb interface under different service conditions,revealing the microscopic mechanism of oxidation corrosion and dissolution corrosion characteristics of the Fe-based alloy:when the oxygen concentration is low,at the solidliquid interface in the LFR,the Fe atoms on the surface of the matrix are dissolved and dissolved in the liquid Pb,leaving vacancies at the same time,Pb atoms immediately enter the Fe matrix to occupy vacancies,continue to dissolve and corrode the matrix,and penetrate the matrix.The dissolution and permeation rates are related to the surface structure of Fe-based alloys,such as the exposed surface Fe atoms at grain boundaries,which are easily dissolved.As the oxygen concentration in the liquid LBE environment increases,O atoms continue to diffuse towards the Fe matrix and aggregate towards the grain boundaries,interacting with alloying elements that segregate at the grain boundaries,and preferentially forming alloy oxides at the grain boundaries.At the same time,the characteristic parameters of atomic interactions at grain boundaries and solidliquid interfaces also provide necessary parameters for simulating the long-term oxidation and dissolution corrosion processes of large-scale surface nanocrystalline Febased alloys,thereby providing a theoretical basis for further predicting the service life of Fe-based structural materials in different oxygen concentration liquid metal environments.