Microscopic Phase Field Simulation For Precipitation Of B2 Ordered Phase In Fe-Al-Cr Alloy

In this paper,based on the microdiffusion phase field dynamics model,taking Fe-Al-Cr alloy as research object,the atomic occupation information on the lattice point is dynamically tracked,and the intrinsic relationship between the precipitation mechanism of the precipitated phase and the environmental variables(alloy composition,aging temperature and elastic distortion energy)is fully revealed,providing atomic scale theoretical reference information for the regulation and design of high performance alloys.The main conclusion of the paper are as follows:(1)The precipitation process of Fe-Al-Cr alloy are clustering of solute atoms,non-stoichiometric B2 ordered phase,stable B2 ordered phase.The precipitation mechanism of the B2 phase is equal composition ordering+unstable decomposition.In the whole process of atomic evolution,there are six types of atomic occupancy,namely the main lattice occupation:Fe _Fe,Al _Al;anti-site defects:Fe _Al,Al _Fe,substitution defect:Cr _Al,Cr _Fe.(2)Considering aging temperature and elastic distortion energy factors individually or in combination,a mutually exclusive relationship between the precipitation and atomic occupancy of two pairs of ordered phases is found.As the temperature increases,the average compositional order parameter and the average long program parameter of the ordered phase decrease,the precipitation rate slows down,and the incubation period becomes longer,which is not conducive to nucleation.At the same time,Fe _Fe,Al _Al,Cr _Fe atomic occupancy probability decreases during the equilibrium period,the atomic occupancy probability of Cr _Al,Fe _Al and Al _Fe increases.At the same temperature,the elastic distortion energy is the opposite of the above effects.However,the occupancy probability of Cr _Fe atoms decreases with the increase of elastic distortion energy during the equilibrium period.(3)The arrangement sequence of atoms in the alloy responds strongly to the alloy composition.As the Al concentration increases,the average order parameter of the ordered phase increases,B2 phase red color deepens,promoting the occupancy probability of Al _Aland Cr _Fe during the equilibrium period,and inhibiting the occupancy probability of Fe _Fe,Cr _Al,Fe _Al,Al _Fe during the equilibrium period.The increase of Cr concentration reduces the average order parameter of the ordered phase,during the equilibrium period,the atomic occupancy probability of Cr _Al,Fe _Al and Cr _Fe increased,while the atomic occupancy probability of Al _Al,Fe _Feand Al _Fedecreased.