Reaction Force Field Molecular Dynamics Study On Corrosion Mechanism Of Fe-H₂O Interface

Fe alloys are widely used as structural materials and condensation pipes in nuclear power pressurized water reactors due to their excellent mechanical properties,resistance to radiation embrittlement,and swelling.Under the environment of high temperature,high pressure,and strong irradiation in the reactor,the iron alloy is in direct contact with water and is easily oxidized and corroded by water molecules,and a large number of oxides are generated on the surface of the iron alloy.The oxide layer of the iron alloy has a loose structure and a large corrosion depth,which will have a great impact on the mechanical properties and mechanical properties of the iron alloy,and will also reduce the working life of the workpiece in the reactor.Therefore,it is of great significance to study the corrosion mechanism of iron in liquid water and the effects of vacancies,scratches,grain boundaries,and irradiation on the corrosion behavior of the molten iron interface.In this paper,we use the molecular dynamics method based on the reactive force field to study the corrosion of iron matrix in water and the effects of defects and irradiation on the corrosion behavior of the molten iron interface.The calculation results in this paper show that:(1)The corrosion process of the iron matrix can be divided into three processes: the adsorption and dissociation of water molecules,the formation and dissolution of iron hydroxide on the surface,and the diffusion of oxygen atoms adsorbed on the surface into the block to form oxides.The orientation of the iron matrix surface will affect the interfacial corrosion of molten iron.The lower the surface energy,the stronger the corrosion resistance.Fe(100)and Fe(110)with lower surface energy have better corrosion resistance than Fe(111).(2)Defects will also affect the corrosion of the molten iron interface.The increase of the vacancy concentration in the iron matrix will accelerate the diffusion rate of oxygen atoms in the iron matrix,increasing the corrosion depth of the iron matrix.Surface scratches will reduce the stability of the iron atomic structure on the surface,causing iron atoms to easily dissolve into water,and oxygen atoms will diffuse into the iron matrix along with the scratches,resulting in localized corrosion.During the corrosion process,the grain boundary will induce the phenomenon of intergranular corrosion,which is related to the internal stress-release at the grain boundary.The grain boundary structure of the polycrystal is complex and the atoms on the grain boundary are unstable.In the early stage of corrosion,a large number of iron atoms in the polycrystal dissolve into the water.Oxygen atoms diffuse into the matrix along the vacancies formed by the dissolution of iron atoms into the matrix to form oxides,resulting in preferential corrosion of grain boundaries.A small amount of intergranular corrosion occurs at the ∑5 twin boundary,and the corrosion of the ∑3 twin boundary and single crystal is uniform.(3)After irradiation,large-scale atomic cascades will occur in the iron matrix,and local melting and recrystallization will occur,while leaving defects such as vacancies and interstitial atoms in the matrix.When the atomic cascade is delivered to the surface,a small amount of oxygen atoms diffuses into the cascade region to form oxides.In this paper,the molecular dynamics method based on the reaction force field is used to study the corrosion process of the molten iron interface,the influence of defects and irradiation on the corrosion of the molten iron interface,and to reveal the relevant corrosion mechanism,which can provide theoretical support for the subsequent development of anti-corrosion materials.