Molecular Dynamics Simulation Of Interfacial Dislocation Network Evolution Of Nickel-Based Single Crystal Superalloy Containing Rhenium

Nickel-based single crystal superalloys not only have excellent mechanical properties such as creep resistance and fatigue resistance,but also have good oxidation resistance and corrosion resistance under high temperature service environment.They have been widely used in the fields of gas turbine thermal power,aerospace and astronautics,especially as key materials for aero-engine turbine blades.The Ni-based single crystal superalloy consists of two phases:theγmatrix phase（disordered Ni-based solid solution）and theγ′precipitate phase（ordered L1₂-type Ni₃Al intermetallic compound）.The interface dislocation network exists between the two phases due to lattice mismatch.Experiments show that interface dislocation is closely related to the excellent mechanical behavior of nickel-based single crystal alloys,which greatly improves the tensile strength and creep resistance of superalloys.It is of great theoretical significance and technical value for the design and development of high temperature structural materials to study the relationship between the interface dislocation network and the mechanical properties of nickel-based single crystal alloys,and to reveal the inherent law of the interface dislocation network hindering the matrix dislocation from destroying the precipitates.The introduction of rhenium into nickel-based single crystal superalloys can effectively improve the mechanical properties of alloy materials,which is called“Re effect”.The rhenium element segregated in theγphase of the matrix has a large molar mass,which has a solid solution strengthening effect,and can increase theγ/γ′mismatch,causing an increase in the density of the interface dislocation network,which helps to hinder the dislocation movement of the matrix.However,the synergistic effect of Re element and interface dislocation network in the tensile or creep stages of alloy materials is difficult to be obtained by low-cost experiments.Based on the molecular dynamics simulation method,a three-dimensional model of nickel-based single crystal superalloys was established in this paper.Using the embedded atom method（EAM）Ni-Al-Re ternary potential function,the effects of interface dislocation network and rhenium element on the mechanical response stage under high temperature,uniaxial tension and creep conditions were studied at the micro-nano scale.The main contents and conclusions are as follows:（1）After the model relaxation is completed,the interface misfit dislocation network at 300 K and 900 K is continuous and the integrity is good;the interface misfit dislocation network at 1500 K is discontinuous and the integrity is poor.In the process of equilibrium,the interface misfit dislocation network in the model changes in morphology and length.The Re atom added to the model enhances the stability of the interface misfit dislocation network by reducing the atomic potential energy of the interface region.（2）According to the variation of dislocation length in matrix phase,precipitate phase and interface region,the whole tensile process is divided into three stages:in the first stage,the dislocation length in matrix phase is constant,and the deformation of model is elastic deformation;in the second stage,the dislocation length in the matrix phase increases obviously,and there is almost no dislocation in the precipitate phase.The deformation of the model is elastic-plastic deformation.In the third stage,the dislocation length in the matrix phase and the precipitated phase increases,and the deformation of the model is plastic deformation.During the tensile process,the atomic self-diffusion coefficient at the dislocation core of the interface region is significantly larger than the overall atomic self-diffusion coefficient of the model,and the atomic movement at the interface dislocation core is more intense,that is,it is easier to form the“groove”phenomenon observed in the experiment in the interface region.（3）The creep of model is different under different stress.At 900 K,the creep phenomenon is not obvious when the stress is 2.5 GPa;when the stress is 3.0 GPa,the creep process is complete and easy to study.When the stress is greater than 3.0 GPa,the model deforms rapidly and destroys quickly.When 3.0 GPa stress is applied to the model at 900 K,the integrity of the interface dislocation network containing Re model in the matrix phase at each stage of the creep process is better than that of the model without Re in the matrix phase,and the interface dislocation network effectively hinders the movement of the dislocation from cutting the precipitated phase.The dislocation movement in the matrix phase leads to the segregation of Re atoms in the interface region.When the dislocation cuts the precipitated phase,it is hindered by more Re atoms in the interface region,thereby delaying the time,during which plastic yield happens in the precipitated phase by cutting,so as to improve the creep resistance of the alloy material.