Effect Of Repeated Nano-cutting On Surface Quality And Subsurface Damage Of γ-TiAl Alloy

γ-TiAl alloy has many advantages,such as low density,high elastic modulus,good flame retardancy and high temperature strength.It has great potential in the fields of medicine,automobile and aerospace.However,due to the brittleness of γ-TiAl alloy at room temperature and difficult deformation machining,residual stress and surface cracks are easy to occur in the machining process,which seriously affects the service performance of the parts.Nano-cutting,as an important means of ultra-precision machining technology,also plays a crucial role in the field of nano-manufacturing,which is the foundation of the development of atomic and near-atomic scale manufacturing technology.In this paper,the molecular dynamics simulation of the repetitive nano-cutting process of single crystal γ-TiAl alloy was carried out to explore the differences between repetitive machining and single machining.The effects of tool geometry parameters on cutting force,friction coefficient,Newton layer mean temperature,surface quality and subsurface damage in the cutting of γ-TiAl alloy were investigated.In this paper,the removal mechanism of single crystal materials in repetitive nano-cutting process was deeply discussed,and the relationship between surface quality and subsurface damage and dislocation and microstructure evolution in repetitive nano-cutting process was clarified,which provided theoretical basis for improving surface quality and mechanical properties of parts in practical machining.The main research contents are as follows:1.The repeated nano-cutting model of single crystal γ-TiAl alloy was constructed by molecular dynamics simulation.The cutting forces,the evolution of microscopic defects,the surface roughness and the residual stress distribution of the machined surface during repeated nano-cutting were compared and analyzed.The results show that the secondary cutting can improve the surface quality and reduce the subsurface damage,but the increase of compressive residual stress and energy required for machining can reduce the plasticity of the machined surface,and the third cutting has no obvious improvement on both.After cutting,the residual compressive stress inside the workpiece first increases and then decreases with the increase of the depth below the workpiece surface,while the residual compressive stress inside the workpiece after secondary cutting increases and becomes more stable,which improves the mechanical properties of the workpiece.2.The molecular dynamics simulation of the repetitive nano-cutting of single crystal γ-TiAl alloy was carried out by using the single factor experiment method with different geometrical parameters of the second cutting tool.The cutting force,chip formation and surface morphology during the repetitive nano-cutting were analyzed.The results show that when the tool front Angle is 15°,the surface roughness is lower and the surface quality is better.The influence of different second cutting tool front Angle on the surface roughness is not strong.The average normal cutting force decreases with the increase of the tool back Angle when the tool front Angle and blunt circle radius are constant.When the critical back Angle of the second cutting of single crystal γ-TiAl alloy is between 10° and 15°,the mean cutting force and roughness of the finished surface do not change obviously when the tool back Angle is larger than the critical back Angle.With the increase of the blunt radius of the second cutting tool,the chip decreases,the subsurface defect increases,and the surface roughness of the machined surface also increases with strong regularity.