Study On Cutting Mechanism Of Nickel-based Alloy Based On Molecular Dynamics

GH4169 is widely used in aerospace field because of its excellent comprehensive properties such as oxidation resistance and high temperature resistance.Most of the critical surfaces of heat-resistant parts are finished by precision cutting or ultra-precision cutting.The research of nano-scale materials has been a hot topic in ultra-precision machining.The study of the cutting process of GH4169 with of the phase or polycrystalline structure under the atomic angle can not only explain the mechanism of the cutting process from the nano-angle,but also reveal the material properties and the wear of the tool in the macro-cutting.The data obtained are analyzed visually by Ovito,and the mechanism of high temperature deformation and the diffusion wear theory of tool materials in the cutting process of Ni-based superalloy materials are studied.In this paper,firstly,a macroscopic turning experiment of GH4169 was made.Through the observation of chip root by SEM and the microscopic metallographic diagrams,the conclusions that the width of shear band decreases with the increase of cutting speed,and the process of chip formation is accompanied by the mechanical breakage and rotation of grains and the migration of grain boundary were drawn.After that,in order to further study the formation mechanism of shear band,the diffusion behavior of workpiece atoms and the microcosmic phase strengthening mechanism in the cutting process,the internal polycrystalline and phase composition of nickel-based superalloy were determined by SEM and HRTEM,so that the polycrystalline and the multi-phase nano-cutting models of nickel-based alloy are determined.At the same time,EAM,Tersoff,potential energy functions were verified through simulation experiments and used to assign the properties of workpiece and tool material.And the Morse potential parameters between tool,workpiece and phase were further calculated and determined.Finally,the whole cutting process simulation is finally completed by the Lammps software.In the molecular dynamics cutting simulation of nickel-based alloy polycrystalline model,through the analysis of atomic shear strain and relative displacement,We analyze the flow effect of workpiece atoms along the [-110] direction in the model,which shows that the cutting region is subjected to shear in this direction.With the advance of the tool and the further extrusion of the workpiece atoms,the shear band is finally formed.On the other hand,by calculating the diffusion activation energy of nickel,iron and chromium atoms in the workpiece and the cutting tool,the conclusions that the atoms in the workpiece material diffuse to the interface between the tool and the chip through the grain boundary,and then they are easier to enter the tool through the grain boundary diffusion of silicon carbide are drown.More specifically,in the grain boundary diffusion,the chromium atom first enters the grain boundary,and then the iron atom enters,and the nickel atom finally completes the diffusion process.Moreover,these atoms will form compounds by bonding after diffusing into the grain boundary of silicon carbide.In the cutting of multiphase model,through the analyzation of the change of shear stress and the stacking fault energy,the dislocation interaction in the cutting process,the number of dislocation pinning points and its variation with temperature,it is concluded that the strengthening mechanism of ?' phase in cutting is that at the beginning of cutting,the ?' phase in the workpiece forms a cross stacking fault through the dislocation constrictions to hinder the deformation of the workpiece,and in the stage of tool contact with the workpiece and causing the plastic deformation,the dislocation in the ?' phase of the workpiece will form a pinning point through the compound action of kink and jog.Specifically,the dislocation density will appear stagnant zone at this stage of cutting process,and the time node in this area will also be very dependent on temperature,and this dependence is further explained from the perspective of the dislocation pinning formation energy.