单晶硅纳米切削机理与微结构演化的内在关联性研究

发布时间：2018-05-01 04:14

本文选题：纳米切削 + 切削原理　；参考：《燕山大学》2015年硕士论文

【摘要】：纳米切削是一种高效、直接的微尺度制造方法,对于国防、航天等领域至关重要。然而对于单晶硅这类脆性材料,加工中材料行为会随尺度变化由发生韧性变形转而发生脆性变形,即在微尺度下无法忽略材料微结构的变化。这种微结构的演化与变形方式的关联性严重制约了加工效率与质量的提高。本文从材料变形角度,利用分子动力学方法,探究了纳米尺度切削原理与微结构演化的关联性关系。首先,本文简述了分子动力学方法的基本思路,分析了金刚石单点切削工艺中的材料去除方式,并结合分子动力学特点,阐述了正交切削模型的建立过程。在合理选择模型参数的基础上,确定了势函数等仿真参数。采用并行计算方法,基于几何模型,构建了单晶硅纳米切削过程的分子动力学模型。其次,分析了单晶硅纳米切削中塑性去除模式的特点。从切屑形成、原子迁移轨迹、切削变形三个方面阐述了塑性去除的变形机理。通过径向分布函数、配位数等多种方法,分析了塑性去除中材料微结构的变化规律,探究了塑性去除过程与微结构演化的联系。计算了塑性去除过程中单晶硅材料的应力分布、势能分布与自由体积变化规律,结合微结构演化特点,说明了应力、自由体积与微结构演化的内在关联性,发现了自由体积与塑性流动的关联关系,说明了宏观切削参数对塑性去除过程的影响关系。最后,分析了单晶硅纳米切削中脆性去除模式的特点。基于金刚石单点切削工艺特点,观察了不同未变形切屑厚度下材料变形方式的差别,分析了相应的微结构变化特点,从相变角度揭示了脆塑转变过程的剪切局部化特征。通过分析剪切带的构成,说明了剪切带承载能力随未变形切屑厚度变化的规律。研究了刃口钝圆半径与晶向对脆性去除过程的影响。从位错密度与位错组态两方面分析了缺陷在脆性去除过程中的作用,揭示了纳米切削过程中单晶硅无法通过位错机制进行塑性变形的原因。计算了脆性去除中的势能与应力分布,说明了脆性变形过程对应的工艺特点。
[Abstract]:Nano-cutting is an efficient and direct micro-scale manufacturing method, which is very important in the fields of national defense, aerospace and so on. However, for brittle materials such as monocrystalline silicon, the behavior of materials changes from ductile deformation to brittle deformation with the change of scale, that is to say, the change of material microstructure can not be ignored at microscale. The relationship between the evolution of the microstructure and the deformation mode seriously restricts the improvement of processing efficiency and quality. In this paper, the relationship between the principle of nanoscale cutting and the evolution of microstructure is studied by molecular dynamics from the point of view of material deformation. Firstly, the basic idea of molecular dynamics method is briefly introduced, and the material removal method in diamond single point cutting process is analyzed, and the process of establishing orthogonal cutting model is expounded according to the characteristics of molecular dynamics. Based on the reasonable selection of model parameters, the simulation parameters such as potential function are determined. The molecular dynamics model of monocrystalline silicon nanocrystalline cutting process was constructed based on geometric model by parallel calculation method. Secondly, the characteristics of plastic removal mode in monocrystalline silicon nanomachining are analyzed. The deformation mechanism of plastic removal is described from chip formation, atom migration path and cutting deformation. By means of radial distribution function, coordination number and other methods, the variation law of material microstructure in plastic removal was analyzed, and the relationship between plastic removal process and microstructure evolution was explored. The stress distribution, potential energy distribution and free volume variation of monocrystalline silicon in plastic removal process are calculated. The intrinsic relationship between stress, free volume and microstructure evolution is explained by combining the characteristics of microstructure evolution. The relationship between free volume and plastic flow is found, and the influence of macro cutting parameters on plastic removal process is explained. Finally, the characteristics of brittle removal mode in monocrystalline silicon nanomachining are analyzed. Based on the characteristics of diamond single point cutting process, the different deformation modes of materials with different thickness of undeformed chip are observed, the corresponding characteristics of microstructure changes are analyzed, and the shear localization characteristics of brittle plastic transition process are revealed from the angle of phase transformation. By analyzing the composition of the shear band, the variation of the bearing capacity of the shear band with the thickness of the undeformed chip is explained. The effects of the radius and orientation of the edge obtuse circle on the brittleness removal process were studied. The function of defects in brittle removal process was analyzed from dislocation density and dislocation configuration, and the reason why single crystal silicon could not be deformed by dislocation mechanism in nanoscale cutting was revealed. The potential energy and stress distribution in brittleness removal are calculated, and the process characteristics of brittle deformation process are explained.
【学位授予单位】：燕山大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ127.2

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