Precipitation Process Of Nickel Base Alloy And The Interatomic Potential Calculation By Microscopic Phase-field Simulation

The microstructure of alloy is largely determined by its precipitation behavior and mechanis, including alloy structure and microstructure morphology, phase precipitation mechanism, the nucleation and coarsening process, the atom clustering and precipitation process, atomic preferred occupation and antisite defect, interface structure and mobility of phase, precipitation sequence and pre-precipitation phase. Compared with the experimental methods, the computer simulation research at atomic level has incomparable superiority and necessity. The interatomic potential is the basis of all calculation about condensed matter at atomic level. Developing the calculation model and method of interatomic potential related to temperature, concentration and structure has important theoretical significance and application value on the the computer simulation for materials.Based on microscopic phase- field dynamics model, the Ni₇₅Al₁₄Mo₁₁ alloy is studied. Firstly, the precipitation process of Ni₇₅Al₁₄Mo₁₁ alloy is simulated. Then we analyses the influence of the four-nearest interatomic potential on precipitation process. Based on these studies, we derived the potential equations of L1₂ and DO₂₂ structure according to microscopic phase field theory, which change with temperature, concentration and structure.By simulating the precipitation process of Ni₇₅Al₁₄Mo₁₁ alloy under 1073 K, we can draw the following conclusions. L₁₀ phase in the evolution of the atomic transition diagram presents two kinds of orientation, which is corresponding to the two kinds of structure in the two-dimensional plan:?- type and ?- type projection. The phase transformation process is the changing process of color and the pccupation probility at sites. The precipitation process of Ni₇₅Al₁₄Mo₁₁ alloy is: the solute atom clustering ? ordering of L₁₀ phase ? formation of L1₂ stable phase, and there is no Ni₃ Mo phase with DO₂₂ structure. ?1 site?surface heart position of face-centered cubic? is gradually occupied by N i atoms. ?2 site?surface heart position of face-centered cubic? is firstly occupied by Al and Mo atoms for a short stage, subsequently, it is replaced by N i atom. ? site?corner site of the face centered cubic? is occupied by Al and Mo atoms, and the occupation probability of Al atoms is always higher than that of Mo atoms. Mo atoms tend to replace Al atoms in Ni₃Al-based alloy, give priority to occupy the Al site. The final equilibrium phase is Ni₃?Al Mo? phase with L1₂ structure.Based on microscopic phase field theory, according to the equation between probability and energy given by Khachaturyan, we derived the potential equations of L₍12 and DO₂₂ structure, which change with temperature, concentration and structure. The potential equations of L1₂ and DO₂₂ structure are: Based on the inversion equations, The first- nearest neighbor interatomic potentials of Ni₃ Al and Ni₃ Mo are calculated. Both of the will change with temperature and concentration linearly. The simulated interatomic potentials are inversed into the microscopic phase field model and the calculated results are in good agreement with the experimental results, which verifies the reliability of the results.Generated by first principles calculation, we found that the generation of Ni₃ Al phase with L1₂ structure is easier than the Ni₃ Mo phase with DO₂₂ structure; and the stability of the Ni₃ Al is better than Ni₃Mo; In addition, Ni₃ Mo phase with DO₂₂ structure belongs to the metastable phase. So it is difficult to form in the phase equilibrium stage during precipitation.