Microscopic Phase-field Simulation Of Precipitation Process And Atomic Site Occupation For Ni₇₅Al₁₄Mo₁₁ Alloy

Nickel-base superalloy is widely used in manufacturing engines and other hot endcomponents for its high-temperature creep degeneration resistance, fatigue resistance,oxidation resistance, corrosion resistance, etc. The research of precipitation processcontributes to an accurate analysis and control of alloy’s microstructure, and then theimprovement of alloy’s properties. Atom site occupation behavior in the microstructure has aclose relation with the mechanical properties, electrical properties, magnetic properties ofmaterials. Therefore, behavior of atom site occupation increasingly become the focus ofresearchers’ attention.Based on the microscopic phase-field dynamics model, precipitation process of theresearch object Ni₇₅Al₁₄Mo₁₁alloy is simulated visually by taking use of MATLAB languageprogram. Firstly, we analyses the influence of temperature on precipitation process andatomic site occupation in Ni₇₅Al₁₄Mo₁₁alloy. Secondly, the influence of elastic energyconstant on precipitation process and atomic site occupation is researched under the action oftemperature coupled with elastic energy. Finally, atomic transition and migration rule at theinterface as well as evolution process of interface is discussed.By simulating the precipitation process of Ni₇₅Al₁₄Mo₁₁alloy under differenttemperature and different elastic energy constant, we can draw the following conclusions.Ni₇₅Al₁₄Mo₁₁alloy is precipitated by solute atom clustering→ordering of L10phase→formation of L12stable phase, and there precipitate no Ni3Mo structure. α site is graduallyoccupied by Ni atoms. β1site is firstly occupied by Al and Mo atoms for a short stage,subsequently, it is replaced by Ni atoms. β2site （corner site of the face centered cubic） is occupied by Al and Mo atoms, and the occupation probability of Al atoms is always higherthan that of Mo atoms. Mo atoms tend to replace Al atoms in Ni3Al-based alloy, give priorityto occupy the Al.Increase of temperature promotes the occupation of antisite atoms, slows down the speedof alloy precipitation, inhibits nucleation as well as ordering process, reduces theconcentration of the ordered phase.With the increase of elastic strain energy, the arrangement of atoms presents increasinglyordered, precipitated phase particles become coarser and preferred orientation is more andmore obvious, the phenomenon of particles’ regularly arranged along the elastic "soft"direction aggravated, so is the characteristic of single orientation for L10phase. While elasticenergy has little effect on precipitation incubation period, it promotes the degree of orderingand their atomic occupation.Due to the formation of Ni3Al is easier than Ni3Mo, and the stability of Ni3Al is higherthan that of Ni3Mo, there precipitate no Ni3Mo structure in Ni₇₅Al₁₄Mo₁₁alloy.While aging at973K, three kinds of interface formed between L12phases inNi₇₅Al₁₄Mo₁₁alloy which are labled interface A, B and C. Interface A is （100） and （200） inalignment, interface B is consisted of one Ni atom plane and （100） and （200） in alignment,interface C is （100） and （100） in alignment. The exchange of Al, Mo atoms on1site with Niatoms on2site leads to the migration of interface A, and the structure of the interface A doesnot change before and after the migration. Although there precipitates Ni and Mo atoms atinterface B and C, no Ni3Mo structure formed, which making these interfaces widened. Thewidth of the interface is various with different interface structure.