【作者】 李德刚；

【导师】 梁迎春；

【作者基本信息】 哈尔滨工业大学 ， 机械制造及其自动化， 2008， 博士

【摘要】 纳米加工技术的发展使得纳机电系统制造成为可能。当被加工材料尺寸达到纳米量级时,由于小尺寸效应、量子效应及表面效应的影响,纳米加工的理论与方法和传统机械加工有着本质的不同,材料的力学特性、缺陷、载荷特性和失效机理等都将发生质的变化。依据经典连续介质力学建立起的机械加工理论将不能直接应用在纳米加工技术当中,必须应用近代物理学的最新成果,从原子尺度上去研究纳米加工机理。本文借助分子动力学仿真技术,探究单晶硅三个典型晶面在纳米压痕及刻划过程中的加工变形机理,应用纳米压痕仪进行相应的纳米压痕及刻划实验。随后探究脆性材料单晶硅的纳米切削机理,并对纳米加工过程中的金刚石刀具磨损进行考察。这对于全面认识单晶脆性材料纳米加工机理具有重要的理论意义和实用价值,同时将为纳米加工技术的进一步发展提供必要的理论基础。本文首先建立了单晶硅(100)、(110)和(111)晶面纳米压痕刻划的三维分子动力学仿真模型,进而研究应用纳米原位压痕仪对单晶硅不同晶面的纳米加工技术,同时考察单晶硅的微观变形机制和力学性能。应用纳米压痕仪对单晶硅不同晶面进行了相应的实验,结果表明:相对(100)、(110)晶面,(111)晶面在仿真过程中得到较小的弹性模量和硬度值,这种现象与仿真结果基本一致;实验中单晶硅各晶面刻划载荷随刻划深度增加而增加并具有不同的上升斜率,其各晶面上升斜率大小关系与仿真中各晶面刻划载荷上升斜率关系一致,间接的证明分子动力学是研究单晶硅纳米加工机理的有效方法,仿真建模中的相关内容基本正确。其次,对于不同晶面单晶硅分别从不同时刻的瞬间原子位置图、变形区结构变化,切削过程中能量的演化、切削力、应力的变化等方面分析了工件纳米切削过程中的变形机理和各向异性对加工过程的影响。从势能、切削力的变化角度可以看出,单晶硅在切削过程中结构发生渐进式变化,并没有位错产生;在工件的切削变形区,切屑的势能分布因不同的晶面结构而略有差别;处于刀具前刀面的被加工材料其变形区域的扩展速度和刀具切削速度处于同一数量级。对单晶硅纳米切削已加工表面质量进行考察,结果表明,已加工表面均方根偏差处于0.01nm量级,应力处于0.01GPa量级,并且其值随晶面不同而有所不同。最后,对单晶硅纳米切削过程中的单晶金刚石刀具磨损机理进行了研究,并考察温度场对刀具磨损的影响。仿真的原子瞬间图显示,工件的挤压导致刀具表面晶体结构发生改变,金刚石刀具表面原子在纳米切削初始阶段产生脱落现象,随后的切削过程中原子脱落现象明显减弱。从径向分布函数判断:刀具的外表层形成散乱结构,同时刀具理想晶格和外表层之间的亚表层的原子密度增加阻止了刀具的进一步磨损。温度升高使得刀具表层及亚表层平均原子势能及其应力增加,切削力略微下降;温度的升高使得单晶硅原子活性显著提高,而对刀具原子的影响并不明显,切削过程在高温条件下可以继续进行。更多还原

【Abstract】 The development of nanometric machining technology makes it possible of manufacturing nano-electromachanical system manufacture. When dimension of the microstructure reaches nanometer scales, nano-masnufacturing theory and method are essentially different from traditional mechanical design and method because mechanical properties, load characteristics and failure mechanism will change intrinsically in such dimensional scale.Therefore, traditional mechanical design theory and method based on classical continuum mechanics can not be applied directly to nanometric machininig technology, and new research method should apply ideas from latest progresses in modern physics to study nano-manufacturing mechanism from the atomic-scale point of view. In this thesis, molecular dynamics (MD) simulation is employed to investigate the deforming mechanism of single crystal silicon planes during nano-indentation and scratching process and relative experiments are carried out. Then the nano-cutting mechanism of brittle material single crystal silicon and researches of diamond tool wear and its effect on cutting process are discussed. The fulfillment of this study has resulted in a better understanding of the nano-manufacturing mechanism of single crystal silicon, and it is of significance for theoretical instruction of practical design and nano-manufacturing processes. Therefore, it will contribute to the fundamental theory of nano-manufacturing for their further development.Firstly, the three dimension simulation models of nano-indentation and scratching of single crystal planes (100), (110) and (111) are set up to make researches on nano-deforming mechanism and micro mechanical properties. At the same time, experiments related to simulation models are carried out. The experimental resulats show that the elastic modulus value of (111) plane is smaller than that of (100) and (110) planes, and the relationship of elastic modulus of the three classical planes is corresponding to that of simulation. For the three planes, the relationship of increasing slopes of scratching loads along with scratching depths is corresponding to that from the experiments.The phenomena mentioned above indirectly prove that MD is effective method to research silicon nano-machining process, and that relative basic theories about building models are right.Secondly, nano-cutting mechanism is studied through analyzing atomic temporal map, structural variation of deforming areas, the development of work piece potential, cutting force and so on, and anisotropic influences on cutting process are studied, also. The simulation results shows that single crystal structure phase change is progressive without dislocations during nano-cutting process according to change process of potential and cutting force; there are differences of potentials in chip area of the three crystal planes; the expanding velocity of deformed area near tool’s rake face is in the same order with cutting speed; on machine surface altitude root mean square deviation is in order of 0.01 nm; stress is in order of 0.01 GPa and there are differences in stress values due to different crystal planes.Finally, diamond tool wear during single crystal silicon nano-cutting is studied, and the effect of temperature viriation on tool wear is researched through building cutting model. According to atomic temporal map, some outdoor atoms of tool are moved in the initial phase of cutting, and then degree of tool wear is reduced obviously in the following cutting process. There are different phase structures formed in the tool during cutting process and the phase structures are analyzed by radial distribution functions. There is an increase of atomic density in subsurface of tool which prevents tool from further wear. Average atomic potentials of tool’s top surface and sub-surface are added with increase of system temperature while the cutting force is lessened. The activity of silicon atoms is raised remarkably due to increase of temperature than that of tool atoms so that the cutting process can be continued steadily.更多还原