Molecular Dynamics Simulation Of The Effect Of Processing Parameters On Nano Cutting Quality Of Single Crystal γ-TiAl Alloy

Because of γ-TiAl alloy has low density,high specific strength and high temperature resistance,it become the most potential high temperature structural material in the field of aerospace and automotive engine.However,γ-TiAl alloy is hard to deform and brittle at room temperature,resulting in subsurface defects and residual stress,which affect its processing quality and restrict the application ofγ-TiAl alloy.In order to prevent subsurface defects and residual stress from adversely affecting the surface quality and mechanical properties of the workpiece,it is necessary to study the formation and evolution mechanisms of defects during processing and the distribution of residual stress caused by processing.The introduction of molecular dynamics method can study the evolution of defects and residual stress distribution caused by cutting process from the atomic point of view,and can explain the influence of different processing parameters on the nano-cutting quality of metal materials from a microscopic point of view.Therefore,in this paper,the molecular dynamics method is used to study the defect evolution,residual stress,cutting force variation and the influence of material plastic deformation on the mechanical properties of single crystalγ-TiAl alloy under different processing parameters.The research works are as follows:(1)The nano-cutting process was simulated by molecular dynamics method,the subsurface defect structure in the cutting process of single crystalγ-TiAl alloy was studied,and the change law of defects such as the transformation of subsurface crystal structure,stacking fault evolution and dislocation evolution of single crystalγ-TiAl alloy during the cutting process is obtained.The results show that the arrangement of crystal atoms is destroyed and transformed into amorphous phase,which is represented by plastic deformation during cutting.Moreover,the HCP atoms generated by the FCC crystal structure transformation have a greater impact on the workpiece,and stacking faults and dislocations continue to evolve as the cutting progresses.(2)The formation and annihilation of stacking faults during the nano-cutting process were studied,the slip direction of stacking faults was analyzed,it was found that the stacking faults mainly evolved and slipped at 45°slip plane along the cutting direction and normal direction,and the generation mechanism and slipping rules of stacking faults are obtained.The change rule of cutting force of single crystalγ-TiAl alloy during the cutting process was analyzed,and the relationship between the evolution of defects and the change of cutting force was obtained,it was found that the ability of the stacking fault evolution to hinder the tool is the main reason for the change in cutting force,which further explained the evolution of microscopic defects on the subsurface of single crystalγ-TiAl alloy mechanism.(3)The effects of different machining parameters(cutting depth,tool edge radius and tool angle)on the nano-cutting quality of single crystalγ-TiAl alloy were studied,and the evolution of micro-defects such as vacancy formation,dislocation reaction,fault slip,etc.on the subsurface of single crystalγ-TiAl alloy under different processing parameters,as well as the evolution of internal stress,the quality of cutting surface,and the formation and change law of chips were analyzed,and the relationship between the evolution of micro-defects and internal stress evolution of single crystalγ-TiAl alloy under different processing parameters is given,as well as the law of residual stress generation.The results show that as the cutting depth increases,the dislocation reaction increases,and due to the atomic bond fracture of the workpiece,the growth rate of the tangential force F_x is greater than the normal force F_y,the quality of the processed surface decreases,and the residual compressive stress along the depth of the workpiece increases;The squeezing effect of the cutting edge radius on the workpiece increases the dislocation response,and the growth rate of the normal force F_y is greater than the tangential force F_x,the quality of the processed surface decreases and the residual compressive stress along the depth of the workpiece increases;The squeezing and blocking effect of the large chip atoms is weakened,and the dislocation reaction is weakened.The reduction rate of the normal force F_y is greater than the tangential force F_x,the quality of the processed surface is enhanced,and the residual stress in the depth direction of the workpiece is reduced.