SiC陶瓷材料刻划去除机理及裂纹扩展行为研究

发布时间：2018-05-26 10:49

本文选题：SiC陶瓷 + 纳米刻划　；参考：《哈尔滨工业大学》2016年博士论文

【摘要】：SiC陶瓷具有硬度高、热膨胀系数小、比刚度高、耐磨损以及耐腐蚀等优点,广泛应用于卫星、航空航天、先进武器、空间望远镜等领域。目前,磨削是SiC材料主要的加工方法,尽管针对该材料的磨削加工表面特征及工艺参数优化进行了一定的研究,但是关于该材料的微观去除机理和裂纹行为仍然模糊不清。因此,深入研究磨削过程中材料去除机理和裂纹扩展机制等基础行为对获得良好的磨削表面质量及较低的亚表面损伤具有重要帮助,然而磨削是一个复杂的过程,很难直接分析其材料去除行为及表面/亚表面裂纹扩展机制,刻划实验是研究材料磨削加工过程中去除行为最常用和有效的方法之一,因此,本文基于刻划实验及仿真对硬脆材料的磨削去除过程及裂纹形式进行了分析。SiC陶瓷是由SiC颗粒烧结而成,材料结构复杂,直接研究难度很大,因此,本文选择了从单晶到陶瓷以及从塑性去除到脆性去除的研究路线。本文主要通过分子动力学仿真、有限元仿真以及不同方式的刻划实验深入研究了反应烧结SiC陶瓷磨削去除及表面/亚表面裂纹扩展机制。为分析SiC材料在磨削去除过程中的微观变形及去除机理,本文利用分子动力学仿真方法分别研究了两种常见单晶SiC(6H-SiC和3C-SiC)的微观动态去除过程。分析了不同形状磨粒对SiC材料去除过程的影响,并对未加工区/已加工区的晶体结构、键长键角分布及高压相变等特征进行了分析,为SiC材料磨削加工过程中塑性去除机理提供了原子尺度的理论解释。本文通过纳米刻划、FIB及TEM等实验及检测手段深入研究了纳米尺度下的6H-SiC和3C-SiC的塑性去除机理,并通过实验直接证实SiC材料的已加工表面存在非晶相,结合分子动力学结果,系统分析了SiC材料的塑性去除机理。反应烧结SiC陶瓷是典型的硬脆材料,该材料在磨削过程中很容易出现断裂甚至是崩碎,深入研究材料断裂特性及裂纹扩展机理有利于理解加工区域裂纹分布特征,进而对抑制加工损伤提供理论指导。然而,该材料为几何结构复杂的多相材料,RBSC复杂随机几何结构直接决定了该材料断裂参数分布的解析解无法获得。因此,本文采用基于虚拟裂纹闭合技术的扩展有限元方法,建立了考虑RBSC材料结构的三维环硅及嵌硅模型,分析了材料结构对裂纹尖端断裂力学参数分布及裂纹动态扩展行为的影响。通过刻划仿真及变载荷的纳米刻划实验,研究了反应烧结SiC陶瓷磨削过程中的裂纹扩展行为及裂纹分布形式,均质材料中的划痕表面/亚表面裂纹形貌规则,很容易区分裂纹形式。但是,受到复杂材料结构的影响,RBSC材料划痕表面/亚表面裂纹形式复杂,经常出现次生裂纹以及无规则的微裂纹。本文利用扩展有限元仿真方法详细分析了刻划过程中不同形式裂纹的扩展过程及分布形式,并对刻划实验中表面/亚表面裂纹分布形式给出了合理解释。综上所述,本文通过SiC材料多形状磨粒刻划仿真及实验,研究了SiC材料去除机理及裂纹扩展行为,为SiC材料精密/超精密磨削及抛光技术研究提供有力支撑,对反应烧结SiC陶瓷磨削裂纹扩展路径及分布形式问题给出了合理解释,该成果为研究降低反应烧结SiC陶瓷磨削表面损伤及亚表面裂纹深度奠定了理论基础。
[Abstract]:SiC ceramics have the advantages of high hardness, small thermal expansion coefficient, high stiffness, abrasion resistance and corrosion resistance. It is widely used in the fields of satellite, aerospace, advanced weapons, space telescope and so on. At present, grinding is the main processing method of SiC materials, although the surface features and technological parameters of the material are optimized. However, the micro removal mechanism and crack behavior of the material are still unclear. Therefore, it is very important to study the basic behavior of material removal mechanism and crack propagation mechanism in grinding process, which is of great help to obtain good grinding surface quality and lower subsurface damage. However, grinding is a complicated process and is difficult to direct. The removal behavior of material and the mechanism of surface / subsurface crack propagation are analyzed. The experiment is one of the most common and effective methods to study the removal of material in the process of material grinding. Therefore, based on the experiments and simulation, the grinding process and the form of the crack in the hard and brittle materials are analyzed and the.SiC ceramics are sintered by SiC particles. In addition, the material structure is complex and the direct research is very difficult. Therefore, this paper selects the research route from single crystal to ceramic and from plastic removal to brittleness. In this paper, the removal and surface / subsurface of reaction sintering SiC ceramic grinding and surface / subsurface are studied by molecular dynamics simulation, finite element simulation and different mode experiments. In order to analyze the micro deformation and removal mechanism of SiC material during the grinding process, the micro dynamic removal process of two kinds of common crystal SiC (6H-SiC and 3C-SiC) was studied by molecular dynamics simulation method. The effect of different shape abrasive particles on the removal process of SiC material was analyzed, and the unprocessed area / addition was added. The crystal structure, the key angle distribution and the high pressure phase transition are analyzed. The theoretical explanation for the plastic removal mechanism in the grinding process of SiC materials is provided. In this paper, the plastic removal mechanism of 6H-SiC and 3C-SiC in nanoscale is studied by nano scale characterization, FIB and TEM and other experiments and detection methods. The amorphous phase existed on the machined surface of the SiC material was directly confirmed by the experiment. The mechanism of the plastic removal of the SiC material was analyzed systematically with the molecular dynamics results. The reactive sintering SiC ceramics were typical hard and brittle materials. The material was easily broken and even broken and broken during the grinding process. The fracture characteristics and crack expander of the material were deeply studied. It is beneficial to understand the characteristics of the crack distribution in the processing area and provide theoretical guidance for the suppression of the machining damage. However, the material is a complex multi-phase material with a complex geometric structure. The complex random geometric structure of RBSC directly determines the analytical solution of the distribution of the fracture parameters of the material. Therefore, this paper uses the virtual crack closure technique to expand the analytical solution. The finite element method is developed to establish a three dimensional ring silicon and silicon embedded model considering the structure of RBSC material. The effect of the material structure on the distribution of fracture mechanics parameters and the dynamic crack propagation behavior at the crack tip is analyzed. The crack propagation behavior in the reaction burning SiC ceramic grinding process is studied by the simulation and the nano scale experiments of the variable load. Crack distribution, the rule of scratch surface / subsurface crack morphology in homogeneous material, is very easy to distinguish the form of crack. However, under the influence of the complex material structure, the scratch surface / subsurface crack form of RBSC material is complex, secondary cracks and irregular micro cracks often appear. This paper uses the extended finite element simulation method in detail. The expansion process and distribution form of different types of cracks in the process are analyzed, and the distribution of surface / subsurface cracks in the characterization experiment is explained. In summary, the mechanism of SiC material removal and the crack propagation behavior are studied by the simulation and experiment of the multi shape abrasive grain of SiC materials. It is the precision / ultra precision of the SiC material. The research of grinding and polishing technology provides a strong support, and gives a reasonable explanation for the path and distribution of the crack propagation in the reaction sintering SiC ceramics. The result lays a theoretical foundation for the study of reducing the surface damage and the subsurface crack depth of the reaction sintering SiC ceramics.
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TQ174.6

【相似文献】