纳米加工晶体铜中亚表层缺陷演变及力学性能研究
发布时间：2018-09-18 17:10
【摘要】：纳米技术在科技日新月异的现代社会已不再是遥远生疏的词汇,基于纳米加工技术的高精度、高质量的工件产品被不断运用在科学研究、国防科技以至高端消费等方方面面。而对纳米加工机理的认识则很大程度上制约了纳米技术的发展。由于纳米加工实验要求以及成本的限制,分子动力学仿真已成为纳米加工领域实用且重要的研究工具。另外,纳米加工领域存在一系列需克服的问题,其中缺乏对工件亚表层缺陷演变规律的理解是制约加工工件质量的重要原因。针对上述问题,本文将晶体铜作为研究对象,包括单晶铜与多晶铜,进行纳米切削以及纳米压痕的分子动力学仿真与实验,分析了单晶铜和多晶铜工件在纳米切削和纳米压痕过程中工件亚表层晶体结构的演变规律,并通过纳米压痕仿真与实验研究了不同切削参数条件下的工件表面力学性能。基于单晶铜纳米切削分子动力学仿真,利用CNA共近邻分析、DXA位错提取等分析方法,分别解构了四面体堆垛层错、V形位错、球形团簇等不同种类亚表层缺陷在工件切削时的演变过程,发现了亚表层缺陷的结构特征以及形成规律;通过改变切削仿真采用刀具的几何参数,包括前角、后角以及刃圆半径,分析刀具参数引起的亚表层结构特征的变化,总结了其对切削过程中位错演变的影响规律。进行多晶铜工件的纳米切削分子动力学仿真,通过切削力、应力分布等方面,研究了切削中多晶铜工件亚表层晶体结构以及位错表现出的规律,通过切削力和工件位错密度表现出的波动规律,发现了多晶铜晶界对位错滑移的阻碍作用以及与位错的转化过程,并发现了多晶铜晶界产生的应力屏蔽现象;改变多晶铜纳米切削仿真时的切削深度,分析切削深度对工件晶体结构以及位错特征的影响,发现了切削深度与工件内部位错密度的线性关系。分别开展单晶铜与多晶铜的纳米压痕分子动力学仿真以及加工实验,对未加工以及经不同切削参数进行纳米切削后的晶体铜工件进行纳米压痕。一方面利用纳米压痕仿真分析了单晶铜的纳米压痕过程,研究了亚表层缺陷对工件压痕再生成位错的影响,并发现亚表层缺陷将造成工件“加工硬化”的现象;同时通过与纳米压痕实验进行对比,发现切削深度的变化对单晶铜工件表面力学性能的影响。另一方面,通过加工与实验比较了不同切削参数下多晶铜工件表面力学性能的差异,发现切削深度的增大在一定范围内使得硬化效果更明显。将纳米压痕仿真结果与实验结果进行对比,发现其趋势的相同特征,从而定性地证明结论的正确性。
[Abstract]:Nanotechnology is no longer a distant and unfamiliar word in the modern society with the rapid development of science and technology. High-precision and high-quality workpiece products based on nanoprocessing technology have been continuously used in many aspects such as scientific research, national defense science and technology, and even high-end consumption. However, the understanding of nano-processing mechanism restricts the development of nano-technology to a great extent. Due to the limitation of experiment and cost, molecular dynamics simulation has become a practical and important research tool in nanofabrication field. In addition, there are a series of problems to be overcome in the field of nano-fabrication, among which the lack of understanding of the evolution law of workpiece subsurface defects is an important reason for restricting the quality of workpiece. In order to solve the above problems, we take crystal copper as the research object, including single crystal copper and polycrystalline copper, and carry out the molecular dynamics simulation and experiment of nano-cutting and nano-indentation. The evolution law of the subsurface crystal structure of single crystal copper and polycrystalline copper workpiece in the process of nano-cutting and nano-indentation is analyzed. The mechanical properties of workpiece surface under different cutting parameters are studied by nano-indentation simulation and experiment. Based on molecular dynamics simulation of monocrystalline copper nanoscale cutting, the V shape dislocation of tetrahedron stacking fault is deconstructed by using CNA conearest neighbor analysis and other analysis methods. The evolution process of different kinds of subsurface defects such as spherical clusters in the cutting process of workpiece is found. The structural characteristics and formation law of subsurface defects are found, and the geometric parameters of cutting tools, including the front angle, are changed by changing the cutting simulation. The change of subsurface structure caused by cutting tool parameters is analyzed, and the influence of tool parameters on dislocation evolution in cutting process is summarized. The molecular dynamics simulation of polycrystalline copper workpiece in nano-cutting was carried out. Through cutting force and stress distribution, the crystal structure and dislocations of polycrystalline copper workpiece were studied. Through the fluctuating law of cutting force and dislocation density of workpiece, the blocking effect of polycrystalline copper grain boundary on dislocation slip and the process of transformation with dislocation are found, and the phenomenon of stress shielding produced by polycrystalline copper grain boundary is also found. The influence of cutting depth on the crystal structure and dislocation characteristics of the workpiece is analyzed by changing the cutting depth of polycrystalline copper nanomachining simulation. The linear relationship between the cutting depth and the dislocation density inside the workpiece is found. The molecular dynamics simulation and processing experiment of nano-indentation of single crystal copper and polycrystalline copper were carried out respectively. On the one hand, the nanocrystalline indentation process of single crystal copper is analyzed by nano-indentation simulation, and the effect of subsurface defects on the dislocation formation of workpiece indentation is studied, and it is found that sub-surface defects will cause workpiece "work hardening". At the same time, the effect of cutting depth on the surface mechanical properties of single crystal copper workpiece was found by comparing with nano-indentation experiment. On the other hand, the difference of mechanical properties of polycrystalline copper workpiece under different cutting parameters is compared with experiments. It is found that the hardening effect is more obvious with the increase of cutting depth in a certain range. The simulation results of nano-indentation are compared with the experimental results, and the same characteristics of the trend are found, which proves the correctness of the conclusion qualitatively.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.11
[Abstract]:Nanotechnology is no longer a distant and unfamiliar word in the modern society with the rapid development of science and technology. High-precision and high-quality workpiece products based on nanoprocessing technology have been continuously used in many aspects such as scientific research, national defense science and technology, and even high-end consumption. However, the understanding of nano-processing mechanism restricts the development of nano-technology to a great extent. Due to the limitation of experiment and cost, molecular dynamics simulation has become a practical and important research tool in nanofabrication field. In addition, there are a series of problems to be overcome in the field of nano-fabrication, among which the lack of understanding of the evolution law of workpiece subsurface defects is an important reason for restricting the quality of workpiece. In order to solve the above problems, we take crystal copper as the research object, including single crystal copper and polycrystalline copper, and carry out the molecular dynamics simulation and experiment of nano-cutting and nano-indentation. The evolution law of the subsurface crystal structure of single crystal copper and polycrystalline copper workpiece in the process of nano-cutting and nano-indentation is analyzed. The mechanical properties of workpiece surface under different cutting parameters are studied by nano-indentation simulation and experiment. Based on molecular dynamics simulation of monocrystalline copper nanoscale cutting, the V shape dislocation of tetrahedron stacking fault is deconstructed by using CNA conearest neighbor analysis and other analysis methods. The evolution process of different kinds of subsurface defects such as spherical clusters in the cutting process of workpiece is found. The structural characteristics and formation law of subsurface defects are found, and the geometric parameters of cutting tools, including the front angle, are changed by changing the cutting simulation. The change of subsurface structure caused by cutting tool parameters is analyzed, and the influence of tool parameters on dislocation evolution in cutting process is summarized. The molecular dynamics simulation of polycrystalline copper workpiece in nano-cutting was carried out. Through cutting force and stress distribution, the crystal structure and dislocations of polycrystalline copper workpiece were studied. Through the fluctuating law of cutting force and dislocation density of workpiece, the blocking effect of polycrystalline copper grain boundary on dislocation slip and the process of transformation with dislocation are found, and the phenomenon of stress shielding produced by polycrystalline copper grain boundary is also found. The influence of cutting depth on the crystal structure and dislocation characteristics of the workpiece is analyzed by changing the cutting depth of polycrystalline copper nanomachining simulation. The linear relationship between the cutting depth and the dislocation density inside the workpiece is found. The molecular dynamics simulation and processing experiment of nano-indentation of single crystal copper and polycrystalline copper were carried out respectively. On the one hand, the nanocrystalline indentation process of single crystal copper is analyzed by nano-indentation simulation, and the effect of subsurface defects on the dislocation formation of workpiece indentation is studied, and it is found that sub-surface defects will cause workpiece "work hardening". At the same time, the effect of cutting depth on the surface mechanical properties of single crystal copper workpiece was found by comparing with nano-indentation experiment. On the other hand, the difference of mechanical properties of polycrystalline copper workpiece under different cutting parameters is compared with experiments. It is found that the hardening effect is more obvious with the increase of cutting depth in a certain range. The simulation results of nano-indentation are compared with the experimental results, and the same characteristics of the trend are found, which proves the correctness of the conclusion qualitatively.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.11
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