Basic Research On Subsurface Defect Evolution Of Ultra-precision Cutting Single Crystal Copper Based On Molecular Dynamics Simulation

The ultra-high compatibility of single crystal copper(111)with graphene makes it an ideal surface for growing single crystal graphene.However,the crystal microdefects produced during the processing are regarded as an important factor that seriously restricts the quality and efficiency of the preparation of single crystal graphene.Therefore,effectively reducing the generation and distribution of subsurface defects during ultra-precision cutting of single crystal copper has become an urgent problem for the single crystal graphene film industry.In view of the constraints of ultraprecision cutting experiments,such as difficulty,long research period and high cost,this paper uses molecular dynamics simulation method to study the crystal microdefects in ultra-precision cutting of single crystal copper.In this paper,the molecular dynamics simulation method is used to study the subsurface defects in the process of ultra-precision cutting of single crystal copper.Based on the establishment of a molecular dynamics simulation model for ultra-precision cutting of single crystal copper(111),not only the effect of dislocation slip on material removal,but also the evolution process of subsurface defects,the transformation relationship between different defects,The effect of different cutting parameters on subsurface defects was investigated.This provides a reliable reference for effectively suppressing the generation of subsurface defects in the process of ultra-precision cutting of single crystal copper(111).The main research work is as follows:(1)A molecular dynamics simulation model of ultra-precision cutting single crystal copper(111)was established and its relaxation process was analyzed to ensure the stability of the simulation model before cutting began.The main slip planes and slip directions of the workpiece material in the process of cutting single crystal copper along different crystal directions were analyzed by CNA analysis.Comparing the main slip surfaces in the same cutting direction with the distribution of burrs on both sides of the machined surface,it is found that whether the distribution of burrs is uniform is directly related to the number of corresponding main slip surfaces and the slip direction.The results show that when cutting along the crystal directions with only one main slip plane,the burrs on both sides of the machined surface are uniformly distributed and the burr height is the lowest.(2)The subsurface defects generated in the process of ultra-precision cutting of single crystal copper(111)were identified by CNA analysis,mainly including "V"-shaped dislocations,prismatic dislocation loops,tetrahedral stacking faults and ladder rod dislocations,etc..On the basis of identifying,marking and tracing various subsurface defects and corresponding dislocation lines,the evolution process of each subsurface defect and the transformation relationship between them were analyzed.The results show that all common subsurface defects originate from stacking faults propagating along different slip planes."V"-shaped dislocation is an important basis for the formation of more complex defects such as prismatic dislocation loops and tetrahedral stacking faults.There is a certain transformation relationship between different subsurface defects,and stacking fault defects with complex structure can also be transformed into cluster defects with relatively simple structure,which is beneficial to the improvement of the surface quality of single crystal copper.(3)By comparing the subsurface defects during ultra-precision cutting of single crystal copper(111)with different cutting parameters,it is found that the cutting depth,cutting speed and cutting direction have significant effects on subsurface defects.The variation trend of cutting depth and cutting speed on the subsurface defect depth under the machined surface is basically the same.When cutting along the incomplete dislocation Burger vector crystal orientation with only one main slip plane,the depth of subsurface defects under the machined surface is the smallest and stable,and the subsurface defects of the material to be machined are uniformly distributed only in front of the tool.