Investigation For Microstructure And Kinetics Evolution Of Precipitates In Ni–Al Alloys

Nickel-based superalloys with excellent high temperature mechanical properties and are choice for hottest parts,such as aircraft engines and industrial gas engines.The long-range orderedγ’phase precipitated in theγphase of the matrix plays a major role in the strengthening of the nickel-based superalloys.Therefore,it is of referenced value to study the microstructure and kinetics ofγ’phase for predicting heat treatment process and microstructure evolution.In this paper,the microstructure evolution and precipitation kinetics ofγ’phase in Ni–Al alloy were analyzed by phase-field method and transmission electron microscopy（TEM）,the microstructures evolution and precipitation kinetics ofγ’phase in two-dimensional and three-dimensional simulation were compared.On this basis,high-throughput simulation is proceeded to study the effect of lattice mismatch and volume fraction on morphology,aspect ratio distribution and coarsening rate of precipitates,and to study the variation of interfacial width ofγ/γ’phase and particles size distribution（PSD）ofγphase in Ni–Al alloy at different aging temperatures.The volume fraction ofγ’phase and the microhardness of alloy increase synchronously at 823K in the Ni-14 at.%Al alloy,meanwhile,the average particles radius of the simulation and experiment is close,and the coarsening rates are k_sim=0.191nm³/h and k_exp=0.214nm³/h,respectively,the quantitative transformation kinetics of two-dimensional and three-dimensional simulation of Ni-17 at.%Al alloy are consistent,indicating that the phase-field simulation can obtain reasonable quantitative results.The processes of nucleation,growth and coarsening overlap each other,the precipitation process is divided into nucleation,growth and early coarsening,quasi-stationary state coarsening and steady-state coarsening stage,according to the variation of the particles number density of theγ’phase in Ni–Al alloy.As the lattice mismatch increases,the phase boundary of theγ+γ’two-phase coexistence zone becomes narrower,the width of the particles size distribution becomes narrower,the peak increases and the peak position r/<r>move to1.0,indicating that the particles size is more uniform.Meanwhile,the average aspect ratio of theγ’phase decreases and the shape of the particles is changed from the interconnected rectangular strips to the individual rectangle.As the volume fraction of theγ’phase increases,the coarsening rate ofγ’phase is reduced first and increased then.When the volume fraction is less than 20%,the coarsening rate decreases as the volume fraction increases,when the volume fraction is 20%³5%,the coarsening rate does not change significantly with the volume fraction,when the volume fraction is greater than 35%,the coarsening rate increases as the volume fraction increases.In high concentration alloys,as the aging temperature increases,the interface width between theγphase and theγ’phase decreases,the peak value of the PSD increases,the peak position moves to the right,and the peak value under inelastic strain is closer to the theoretical prediction of LSW.