Simulation Study On Hydrostatic Stress Influence Of Microstructure Evolution In Single Crystal Silicon Nanomachining

Monocrystalline silicon is a typical brittle material,when using diamond single point turning process for its nano-machining,with the change of cutting scale,monocrystalline silicon will exist brittle removal state,brittle plastic transformation process and plastic removal state,and the essence of this cutting characteristics is generated by the internal microstructure of monocrystalline silicon material changes.The change of hydrostatic stress during the cutting process affects the change of internal microstructure of the material.Therefore,this paper investigates the effect of hydrostatic stress on the microstructure evolution during the nano-cutting process of single-crystal silicon using molecular dynamics methods from the microscopic scale.Firstly,in order to observe the microstructural changes during the whole cutting process,reasonable model parameters were selected to construct an orthogonal cutting model for single crystal silicon nano-cutting;the advantages and limitations of several commonly used microstructure identification methods in identifying the phase transition and dislocation structures were compared and analyzed,and the coordination number method,diamond structure identification method and dislocation extraction method were selected to study the microstructural changes during the cutting process.Subsequently,the single crystal silicon nano-cutting process was classified into three removal states: plastic removal,brittle-plastic transformation process and brittle removal in terms of chip morphology and depth of cut.The effects of hydrostatic stress on the evolution of microstructure during the cutting process were investigated by analyzing the composition and changes of microstructure,the distribution and changes of hydrostatic stress during different removal processes by coordination number method,diamond structure identification method and atomic transient diagram for the plastic removal process,brittle plastic transformation process and brittle removal process simulations,respectively.It was found that high hydrostatic pressure is a condition for the phase transition of single-crystal silicon,and the structure of single-crystal silicon phase transition varies with different levels of hydrostatic pressure.The change from concentrated to localized distribution in the region of high hydrostatic pressure is an important reason for the brittle-plastic transition in single-crystal silicon nano-cutting.The change of hydrostatic stress value during cutting was calculated and analyzed,and it was found that the change of phase transition atomic composition structure due to the change of hydrostatic stress level is also one of the reasons for the brittle-plastic transition in single-crystal silicon nano-cutting.Finally,the effects of tool front angle and tool edge radius on hydrostatic stresses as well as microstructure were investigated.By combining the coordination number method and atomic transient diagrams,the differences in microstructure and hydrostatic stress between different tool front angles and tool edge radii were compared,and it was found that increasing the tool front angle and tool edge radius could change the distribution of the high hydrostatic stress region,affect the distribution of phase change atoms and the change of phase change structure composition,and increase the critical value of the brittle-plastic transition.