单晶锗微纳米切削脆塑转变机理研究

发布时间：2018-08-12 11:16

【摘要】：随着微纳米加工技术的不断发展,单晶锗等脆性材料在红外光学、微机电系统等高科技领域的应用日益广泛,这些领域对材料的表面加工精度已经达到了纳米量级,这就需要超精密的加工理论和方法作为支撑。在纳米加工过程中,为了使单晶锗等脆性材料以塑性切削的方式去除从而获得高质量的光学表面,其关键是控制条件实现脆塑转变,这往往需要把切削深度控制在纳米量级。由于单晶锗是硬脆材料并存在各向异性,确定脆塑转变临界切削厚度对实现脆塑转变从而切削出一致光滑的表面至关重要。但单晶锗等脆性材料的塑性域切削一直没有形成统一的理论认识和加工方法。本文借助分子动力学仿真、纳米压痕和划痕实验及理论分析等方法研究了单晶锗不同晶面在切削过程中的塑性域切削机理。通过对单晶锗脆塑转变机理的研究,获取了单晶锗脆塑转变临界切削深度。这对于深入理解单晶锗等脆性材料纳米切削机理具有重要的理论意义和实用价值。首先对单晶锗(100)、(110)和(111)晶面进行纳米压痕仿真和实验研究。并建立了压痕仿真模型。对不同晶面的微观变形机理和力学特性进行了深入探究。研究结果表明:单晶锗(111)晶面相比于其它晶面具有较小的弹性模量和硬度值,这种现象实验和仿真结论基本一致。随着压入深度增加,单晶锗各晶面的硬度与弹性模量都表现出尺寸效应现象,并且在加载和卸载过程中有突进和突退现象发生,划分了单晶锗在不同加载深度下对应的不同变形阶段。其次,对单晶锗不同晶面进行变深度切削的分子动力学仿真,并建立了变深度切削模型,通过对仿真切削过程中切屑的形成和切削力的变化分析得到了单晶锗弹性变形和塑性去除的两个不同阶段,并得到了弹塑性转变的临界切削厚度和切削力,(100)晶面发生弹性变形和塑性切削的临界切削厚度和切削力分别为0.48nm和42nN。然后研究了不同的切削速度、切削厚度、切削晶面和刀具前角等加工参数对单晶锗弹塑性变形和表面质量的影响,从去除方式、原子变化、势能和切削力变化的角度分析,得出了不同切削参数对单晶锗内部结构变形和表面质量的影响机制,以及不同晶面的各向异性差异。最后,通过单晶锗纳米刻划实验,确定了单晶锗脆塑转变的临界切削深度和范围及变化规律,并对切削过程中的影响因素进行了分析。同时针对单晶锗刻划中的各向异性现象进行了不同晶面的刻划实验,总结脆塑转变临界切削深度的各向异性。并对单晶锗脆塑转变临界切削深度进行了理论预测。结果表明:(100)晶面因其具有最小表面密度、最深脆塑转变深度,在划痕过程中发生脆塑转变最晚,而且随着划痕速度的增加,脆塑转变临界深度和临界载荷也相应增加。
[Abstract]:With the development of micro and nano processing technology, brittle materials such as single crystal germanium have been widely used in infrared optics, micro electromechanical systems and other high-tech fields. The surface processing accuracy of these fields has reached nanometer order of magnitude. This needs the ultra-precision processing theory and the method as the support. In the process of nanocrystalline machining, in order to remove the brittle materials such as germanium by plastic cutting and obtain high quality optical surfaces, the key point is to control the conditions to achieve brittle plastic transition, which often requires the depth of cutting to be controlled in nanometer order. Because single crystal germanium is a hard brittle material and anisotropy exists, it is very important to determine the critical cutting thickness of brittle plastic transition to realize brittle plastic transition and to cut a uniformly smooth surface. However, the plastic domain cutting of single crystal germanium and other brittle materials has not formed a unified theoretical understanding and processing methods. In this paper, the plastic cutting mechanism of single crystal germanium in different crystal faces in cutting process has been studied by means of molecular dynamics simulation, nano-indentation and scratch experiments and theoretical analysis. The critical cutting depth of single crystal germanium brittle plastic transition was obtained by studying the mechanism of single crystal germanium brittle plastic transition. It has important theoretical significance and practical value for further understanding the mechanism of nanoscale cutting of single crystal germanium and other brittle materials. At first, the nanocrystalline indentation simulation and experimental study of single crystal germanium (100), (110) and (111) crystal face were carried out. A simulation model of indentation is established. The microscopic deformation mechanism and mechanical properties of different crystal planes were studied. The results show that the values of elastic modulus and hardness of single crystal germanium (111) crystal face are smaller than those of other crystal masks, which is consistent with the experimental and simulation results. With the increase of indentation depth, the hardness and elastic modulus of each plane of single crystal germanium show the phenomenon of size effect, and during loading and unloading, the phenomenon of breakout and sudden retreat occurs. The different deformation stages of single crystal germanium at different loading depths were divided. Secondly, the molecular dynamics simulation of variable depth cutting on different crystal faces of single crystal germanium was carried out, and the model of variable depth cutting was established. Two different stages of elastic deformation and plastic removal of single crystal germanium were obtained by analyzing the formation of chip and the change of cutting force in the process of simulated cutting. The critical cutting thickness and cutting force of elastic-plastic transformation are obtained. The critical cutting thickness and cutting force of (100) elastic deformation and plastic cutting are 0.48nm and 42 N, respectively. Then, the effects of different cutting speed, cutting thickness, cutting crystal plane and cutting tool front angle on the elastoplastic deformation and surface quality of single crystal germanium are studied. The changes of removal mode, atomic change, potential energy and cutting force are analyzed. The influence mechanism of different cutting parameters on the deformation and surface quality of single crystal germanium was obtained, and the anisotropy of different crystal planes was also obtained. Finally, the critical cutting depth and range of single crystal germanium brittle-ductile transition and its variation law were determined by the experiment of single crystal germanium nanocrystalline delineation, and the influencing factors in the cutting process were analyzed. At the same time, the anisotropy of single crystal germanium has been studied and the anisotropy of critical cutting depth of brittle plastic transition has been summarized. The critical cutting depth of single crystal germanium brittle plastic transition was predicted theoretically. The results show that: (100) because of its minimum surface density and the deepest depth of brittle plastic transition, the brittle plastic transition occurs late in the scratch process, and the critical depth and critical load of brittle plastic transition increase with the increase of scratch velocity.
【学位授予单位】：昆明理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN304.11

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