Molecular Dynamics Research On Plastic Deformation Mechanism Of Nickel Based Single Crystal Superalloy

Due to their excellent creep resistance and high strength,nickel-based single crystal superalloys are widely used in high temperature service parts such as turbine engine blades.γandγ’phase are two common phases in nickel-based single crystal superalloys,and the difference of lattice parameters betweenγandγ’phase will cause the appearance of interface mismatch dislocation,which will have a great influence on the deformation behavior and mechanical properties of nickel-based single crystal superalloys.Therefore,theγ/γ’two-phase structure is used as a carrier to carry out related researches in this paper.At present,the plastic deformation mechanism of nickel-based superalloys is mainly speculated by observing the dislocation and stacking fault after deformation by transmission electron microscopy.Although in situ transmission dynamic observation can be achieved in the process of deformation,dislocation motion is too faster to observe the dislocation reaction process.The molecular dynamics method can realize the real-time tracking of atomic motion information,which can solve the above problems.Therefore,in this paper,the microplastic deformation mechanism of nickel base single crystal superalloy will be studied by molecular dynamics method.In this paper,Ni/Ni₃Al/Ni atomic sandwich model was established according to the microstructure characteristics of nickel base single crystal superalloy,the embedded atomic potential of Ni-Al system was selected to do the simulation under different loads,different deformation temperatures and different strain rates through molecular dynamics method.For uniaxial tension,the effect of temperature on the yield strength is different at different strain rates.However,in the uniaxial compression process,the influence of temperature on the yield strength of nickel base single crystal superalloy is almost not affected by the strain rate,which is that the yield strength decreases with the increase of temperature.In addition,under uniaxial tensile loading,the yield strength of the nickel-based single crystal superalloy almost always decreases with the decrease of strain rate in the temperature range from 300 K to 1300 K.However,under uniaxial compression loading,the strain rate has almost no effect on the yield strength of the nickel-based single crystal superalloy at low temperature（300 K-700 K）.Only at high temperature（900 K-1300 K）,its yield strength will decrease with the decrease of temperature.For the tensile and compression cyclic loading,cyclic hardening will always occur in the early stage of fatigue at different temperatures,and the cyclic saturation phenomenon will appear in the subsequent cycle process,and the cyclic stress amplitude in the saturation stage will decrease with the increase of temperature.By analyzing the characteristics of dislocation evolution and planar defect evolution during the simulation process,the microplastic deformation mechanism and the effect of temperature and strain rate on the deformation mechanism of the nickel base single crystal superalloy were revealed.Under uniaxial tensile loading,temperature and strain rate have effects on the deformation mechanism at the stage of complete plastic deformation.However,under uniaxial compressive loading,temperature and strain rate only have effects on the deformation mechanism at high temperature.In the tensile/compression cycle loading,the failure process of interfacial dislocation occurs at the early stage of the cycle.In the fatigue saturation stage,the deformation mechanism of the nickel-based single crystal superalloy is that the extended dislocation reciprocates between the two phases at room temperature.When the temperature is higher than or equal to 500 K,the deformation mechanism changes to that the extended dislocation reciprocates in the Ni phase.