Evolution Of Precipitation Microstructure Of FeCuMn Alloy Under Internal Magnetic Energy By Continuous Phase-field Method

Fe Cu Mn steel is widely used in pipe matrrial and reactor pressure vessel materials?RPV?of nuclear power station.Under the continuous neutron irradiation,high-density nano Cu-rich clusters are easy to precipitate,which affect the service life of the materials.Due to the existence of ferromagnetic elements Fe and Mn,internal magnetic energy⁸2),)will be generated in the system.It will affect the formation rate,structural transformation and density of nano Cu-rich phase when taking⁸2),)into account Gibbs free energy.At the same time,under the service condition of pressure,the strain will also affect the morphology and precipitation dynamics of Cu rich precipitates.In this paper,the evolution kinetics of Microstructure in aged ternary Fe-Cu-Mn alloy is studied by continuous phase field method,based on the approximate model of subnormal solution.Taking Fe-15at.%Cu-3at.%Mn alloy as an example,when the effect of internal magnetic energy is ignored,the Cu-rich phase forms in the early aging stage;but under the effect of internal magnetic energy,the small component fluctuation of Cu begins to appear in the matrix,indicating that the internal magnetic energy,as the nucleation resistance,can prevent the phase separation of the Cu-rich precipitates;the internal magnetic energy can also prevent the growth and coarsening of the Cu rich phase,and delay the transformation of the Cu rich phase from BCC structure to FCC structure.After the formation of nano Cu rich precipitate,Mn atoms begin to fluctuate and tend to gather at the center of Cu rich phase.Then,Mn atoms in the precipitation began to gather towards the interface,forming a ring/core precipitated form with Mn intermetallic ring and Cu rich phase core.Under the effect of internal magnetic energy,the core-shell structure of precipitated phase could be accelerated.Reducting the ferromagnetic element Mn content in Fe-Cu-Mn alloy will increase the internal magnetic energy and hinder the phase separation and later coarsening of Cu rich phase,while increase of Mn content will decrease the internal magnetic energy and promote the phase separation,growth and coarsening of Cu rich phase.Mn composition of Fe-Cu-Mn alloy is positively correlated with the formation of core-shell structure of Mn rich intermetallic shell and Cu rich phase core,which indicate that reduce ferromagnetic elements Mn content of Fe-Cu-Mn alloy can delay the transformation of Cu rich phase from?-Cu with BCC Structure to?-Cu with fcc structure.The external strain mainly regulates the coarsening process of Cu-rich precipitates.With the increase of applied strain,the shape of Cu rich phase in Fe-15at.%Cu-1at.%Mn alloy is more obvious along the strain direction.In addition,the increase of applied strain is conducive to the formation of core-shell morphology and the structure transformation of Cu rich phase.The reason is that compared with the spherical Cu rich phase,the long-rod Cu-rich phase accelerates the diffusion of Mn to the interface of Cu rich phase,thus accelerating the evolution of Cu rich phase.When the strain is increased?0.03?,the average particle size of Cu rich phase will increase,but when the applied strain is too large?0.05?,the particle size radius will decrease.