Research On The Evolution Mechanism And Process Optimization Of Crystal Copper Nano-cutting Defects

With the continuous development of modern science and technology,computer chips,medical nano-robots,national defense and aerospace and other fields have put forward higher requirements for the dimensional accuracy and surface topography accuracy of workpiece products.However,the improvement of nano-processing quality is limited by the evolution mechanism of subsurface lattice structure defects in materials,and the surface forming mechanism and subsurface defect evolution mechanism of materials need to be studied in depth.After a large number of simulations and experimental results,molecular dynamics methods have become an effective tool for studying nano-fabrication processes,and have been widely used by scholars at home and abroad.In this paper,the molecular dynamics method is used to establish a crystalline copper nano-machining simulation model,and the molecular dynamics simulation of nano-cutting and nano-indentation is carried out,so as to explore the evolution of subsurface defects and the change of processed surface quality of crystalline copper during nano-machining.Through the nano-processing experiment,the simulation results are qualitatively verified,and the optimized process parameter interval of single-crystal copper nano-processing is obtained,so as to improve the accuracy and surface quality of crystalline copper nano-processing.The main contents of this article are as follows:Firstly,based on the molecular dynamics simulation of single-crystal copper nano-cutting,the damage mechanism of single-crystal copper nano-cutting subsurface dislocation defects is expounded.CNA co-neighbor analysis and DXA dislocation extraction method were used to analyze the internal dislocation nucleation,diffusion and annihilation processes of single-crystal copper,and elaborate the nano-cutting mechanism of single-crystal copper.Clarify the evolution of tetrahedral stacking faults,V-shaped dislocations,spherical clusters and dislocation ring defect structures in single-crystal copper subsurface layers with tool cutting.The influence of processing parameters on the surface quality and internal dislocation defect evolution of single-crystal copper nano-cutting is summarized,and the results show that the nano-cutting surface quality of single-crystal copper workpiece is higher at cutting speed of 200 m/s and cutting depth of 3 nm,and the internal dislocation defect structure is small.Secondly,based on the molecular dynamics simulation of nano-cutting of twin copper,the mechanism of nano-cutting of twin copper was studied.It focuses on the cutting effect of the tool at the lattice node,explores the evolution law of the internal defect structure of the grain during the cutting process of the tool,and clarifies the hindrance effect of grain boundary on tool cutting and dislocation propagation.By analyzing the mutual conversion process of grain boundary and dislocation during cutting,the dislocation-grain boundary interaction inside the twin copper is clarified,and the formation process of the "grain boundary-like" structure is revealed.The von Mises and other effect force clouds in the process of twin copper nano-cutting were analyzed,and the stress shielding effect of stress-induced dislocation defect structure diffusion and grain boundary were described,and it was found that the equivalent force values of the cutting area and grain boundary of the tool were high.Changing the cutting simulation parameters,it is concluded that the larger the cutting speed,the smaller the cutting depth,and the higher the surface quality of the twin copper specimen.Finally,single-crystal copper nano-indentation simulation and nano-fabrication experiments are carried out.Combined with the load change during the loading-unloading process of the indenter and the internal dislocation expansion and annihilation of the single crystal copper specimen,the mechanism of single crystal copper nano-indentation was revealed.The molecular dynamics simulation of nano-indentation of single crystal copper under vacuum medium and water medium was carried out respectively,and through the analysis of temperature field and dislocation density,it was concluded that aqueous medium can greatly reduce the nano-indentation temperature field.The nano-indentation and nano-marking experiments were carried out on single crystal copper specimens to explore the processing results under actual working conditions,and the experimental results showed that the processing quality was higher when the marking speed was 100 μm/s and the marking load was 30 m N.This paper has certain significance for in-depth understanding of the crystalline copper nano-processing mechanism and improving the accuracy and surface quality of crystalline copper nano-processing,and provides theoretical data support for improving the quality of nano-processing.