Study On The Instrinsic Relationship Between Nanometric Cutting Mechanism And Microstructure Evolution Of Single Crystal Silicon

Nanometric cutting is a kind of direct manufacturing method with high efficiency in micro scale, which is crucial to areas such as defense and aerospace technology. However, for brittle materials such as single crystal silicon, the material behavior in machining process will change with scale from ductile deformation to brittle deformation, which means that in micro scale the change of micro structure of the material cannot be ignored. The relationship between micro structure evolution and deformation mode has limited the improvement of machining efficiency and quality seriously. In this paper, the relationship between the cutting principle in nano scale and micro structure evolution is studied using molecular dynamics simulation method from the perspective of material deformation.Firstly, the basic ideas of molecular dynamics method are briefly introduced in this paper, and the material removal mode in single point diamond cutting process is analyzed. Considering the characteristics of molecular dynamics, the establishment process of orthogonal cutting model is described. Based on the reasonable selection of model parameters, the simulation parameters such as potential function are determined. By parallel computing method, the molecular dynamics model of single crystal silicon nanometric cutting process is constructed based on the geometric model.Secondly, the characteristics of the ductile removal mode in the nanometric cutting of single crystal silicon are analyzed. The deformation mechanism of ductile removal is described in three aspects: chip formation, cutting deformation and atom motion path. By the methods of radial distribution function, coordination number and so on, the changing rules of material micro structure in ductile removal are analyzed, and the relationship between ductile removal process and micro structure evolution is investigated. Stress distribution, energy distribution and the change rule of free volume of single crystal silicon in the ductile removal process are calculated. Considering the characteristics of micro structure evolution, the intrinsic relation among stress, free volume and micro structure evolution is explained. The relationship between free volume and plastic flow is found, and effects of macro cutting parameters on the ductile removal process are summarized.Finally, the characteristics of the brittle removal mode in the nanometric cutting of single crystal silicon are analyzed. Based on the characteristics of single point cutting process, differences of material deformation mode under different undeform chip thickness are observed, and related micro structure evolution characteristics are analyzed, which reveals the shear localization in brittle ductile transition from the perspective of phase change. Through the analysis of shear band composition, rules of shear band bearing capacity variation with undeformed chip thickness are il ustrated. Effects of cutting edge radius and crystal orientation on the brittle removal process are studied. From the aspects of dislocation density and dislocation configuration, effects of defect on the brittle removal process are analyzed, and the reason why the dislocation-based plastic deformation of single crystal silicon cannot happen in nanometric cutting process is explained. The stress and potential energy distributions in the brittle removal are calculated, and the technological characteristics of the brittle deformation process are explained.