Study On The Relationship Between Microstructure And Cutting Force Of Monocrystalline Silicon In Nano Cutting

There is a brittle-ductile transition in the process of single crystal silicon processing by diamond single point turning process.Monocrystalline silicon can get better surface quality in ductile removal mode.Under brittle mode,cracks and pits will appear on the machined surface,which seriously affects the surface quality and performance of monocrystalline silicon.The brittle-ductile transition phenomenon of monocrystalline silicon is closely related to its mechanical properties.In this paper,molecular dynamics method is used to explore the relationship between the mechanical parameters of cutting process and the evolution of microstructure in brittle-ductile transition,so that the understanding of the mechanism of brittle plastic transformation can be deepened.Firstly,in order to simulate the nanometric cutting process,the cutting process of single point diamond cutting process is analyzed,and the orthogonal cutting model of monocrystalline silicon nanometric cutting is established based on the undeformed chip thickness.Then,the critical condition of nanometric cutting brittle-ductile transition of monocrystalline silicon is analyzed.The critical criterion of different cutting stages is explained based on the parameters of undeformed chip thickness and diameter depth ratio.The critical cutting scale is about 9nm,and the ratio of diameter to depth is about 0.3.Finally,a viewpoint that the leading role of cutting force has led to the occurrence of brittle-ductile transition is put forward.Secondly,aiming at the ductile removal process of nanometric cutting,through the radial distribution function and the identify diamond structure method,we explored the change characteristics of microstructure in the process of ductile removal and the characteristics of the stress change during the plastic removal process are analyzed.Then the chip layer and the machined surface layer are divided into zoning,and the mechanical nature of the material removal is further explained by the calculation of the regional stress.Finally,the average cutting force is calculated,and the mechanism of cutting force on microstructure evolution is explored.It is found that the generation of phase transition atoms and the relaxation are generated by a relatively small cutting force and stress.Then,aiming at the characteristics of brittle mode removal,the essence of brittle removal microstructure evolution is analyzed from the perspective of shear band formation mechanism,the stress value in the process of brittleness removal is calculated,and the stress is the key factor for the formation of the shear band.Finally,the average cutting force under the brittle removal mode is calculated,and the effect of cutting force on the shear band formation is explored.A higher cutting force is obtained,which overcomes the compressive strength of materials and leads to the formation of shear bands.Finally,the influence of three key factors,including undeformed chip thickness,tool rake angle and crystal orientation,on the distribution of phase transformation,chip formation and cutting force during cutting process is explored.At the same time,the average cutting force of the unit is calculated,combined with the nanoscratch experiment,the simulation results were verified from the perspective of workpiece morphology and cutting force variation characteristics.