Deformation Mechanism Of Cutting Ni-Base Superalloy GH4169 Based On Strain Gradient Theory

GH4169 material is composed of many complex elements,with high strength,high temperature oxidation resistance and good thermal stability,which is widely used in aerospace,aviation and other fields.However,due to the poor machining performance of GH4169,there are always factors such as high cutting temperature,complex cutting deformation and severe tool wear in the process of cutting,which are widely studied and discussed by scholars.Therefore,it is of great value to study the cutting deformation behavior of nickel base superalloy.In order to save cost and improve machining efficiency,a large number of researchers choose to use the finite element method to simulate the cutting process.In the process of modeling,the constitutive equation of materials plays an important role,at present,the traditional Johnson cook(JC)constitutive model can effectively simulate the mechanical properties in the cutting process,but the scale characteristics contained in the material are not considered in the traditional JC constitutive model,which ignores the inherent scale effect of the material.Therefore,the traditional JC constitutive model does not have the characteristic of effective size effect,and then it is unable to obtain the accurate size of stress,strain and temperature.In this paper,by introducing the strain gradient theory,the constitutive equation which can reflect the scale effect is established,and the two-dimensional dynamic finite element simulation model of GH4169 cutting process is established by secondary development and compilation of the finite element analysis software.The results of the simulation model are compared with those of the experiment.The results show that the two-dimensional dynamic simulation model can better show the effects of temperature,strain gradient,equivalent stress and scale effect on the cutting deformation.Due to GH4169 material contains ?'(Ni3Al)strengthening phase,considering that this strengthening phase will have a certain impact on the cutting deformation process,so,in this paper,GH4169 cutting simulation model with ?' of coherent element is established,The effects of cutting on stress,strain,temperature and the distribution of stress field at the crack tip caused by ?' phase are analyzed from the point of view of material micro-plasticity mechanics and material dislocation theory.The effect of strain gradient hardening is studied by changing the size of ?' phase.A large number of plastic deformation behaviors have taken place under different deformation temperature and strain rate.Uneven cutting deformation leads to the formation of serrated chips.Combined with the stress-strain curve obtained by the Hopkinson bar experiment at high temperature and high strain rate,the deformation behavior of the material in high-speed cutting process is studied.The constitutive model of materials is established to describe the hardening behavior of materials during deformation.According to the dynamic recrystallization dynamic equation,a dynamic model reflecting the dynamic recrystallization behavior is proposed.Based on the dislocation driving theory and the grain growth dynamic theory,a cellular automaton model(CA)which can simulate the grain growth is established by using MATLAB programming.The model comprehensively considers a series of processes such as grain growth,dislocation density evolution and recrystallization nucleation.The model can be used to simulate the dynamic recrystallization of shear band at high temperature and high strain rate.