Study On γ’ Phase Evolution In Nickel-base Single Crystal Superalloy By Phase Field Simulation

Nickel-base single crystal superalloy has excellent mechanical behavior under high temperature,and is typically used in the hot end components of aviation engines and industrial gas turbine blade.Volume fraction,size,morphology and space distribution of γ’determine the material’s macroscopic mechanical properties,such as strength,plasticity and fracture toughness,creep and fatigue resistance.Study on microstructure evolution is significant for optimizing material aging process and improving the alloy performance.Based on CALPHAD thermodynamic data,using the KKS phase field model and microscopic elastic theory,a 3D phase field for γ’ phase evolution in Ni-Al binary alloy is established.Programming with Intel Visual Fortran and MATLAB,the model is solved under periodic boundary condition with Semi-implicit Fourier spectrum method.The 3D evolution of ordered γ’ precipitating from disordered γ substrate in the nickel base single crystal superalloy Ni-18at.%A1 during 1000K aging process is simulated and studied.The results show that the morphology and distribution of γ’ in simulated Ni-18at.%Al alloy having aged at 1000K for 16h coincide with the TEM image of the experimental results.During the coarsening process,the radius is proportional to the cube root of the time.Volume fraction of γ’ is 32%.Coarsening kinetic index is 3,and coarsening rate constant K=23.4 nm3/h.The size distribution shows good agreement with the LSW theory.the interface structure of nickel-based alloy which appears with precipitationThe ordered domain interface structures produced during the precipitation process of nickel-based single crystal superalloy also have some influence on the morphology and distribution of the γ’ phase.During the growth of γ’ precipitations,γ’ precipitations with the same domain coalesce along specific direction,while the interfaces of γ’ precipitations with different domains met at first and then separate,even both have concaves finally,under the influence of antiphase domain energy.Under the influence of the elastic stress caused by γ/γlattice strain,gradually,shape of γ’turns from sphere to cube or cuboid,arrangement of γ’ changed from irregular random arrangement to rule arrangement along the elastic soft direction.During the coarsening,Elastic strain energy plays a dominant role,which makes a inhibitory effect on γ’ growth.Growth of γ’ along[110]direction is significantly faster than the one along[100]direction.