【作者】 方斌；

【导师】 黄传真；

【作者基本信息】 山东大学 ， 机械制造及其自动化， 2007， 博士

【摘要】 陶瓷刀具以其较高的硬度、良好的耐磨性和高温稳定性，已经成为高效高精密加工的重要刀具之一。但是陶瓷刀具材料的断裂韧度仍偏低，其力学性能的高低主要取决于微观组织结构，为此有必要对陶瓷刀具材料的微观组织结构进行模拟和优化设计，为进一步提高陶瓷刀具材料的断裂韧度提供理论指导。本文利用Monte Carlo Potts模型模拟烧结过程中陶瓷刀具材料微观组织结构演变，系统研究了Monte Carlo Potts模型的模拟算法，提出了新的H-FMonte Carlo模拟算法，并进行了实验验证。研究了Monte Carlo Potts模型及Monte Carlo模拟算法，提出了H-FMonte Carlo模拟算法，该算法首先对随机选择的当前晶格点阵进行晶粒边界判断，仅对处于晶粒边界上的晶格点阵进行重新取向尝试，提高了模拟效率。基于微软公司开发的Visual C++6.0平台，利用C++语言，对H-F Monte Carlo算法和R-Z Monte Carlo算法进行编程，开发了H-F Monte Carlo模拟算法程序（H-F MCSPⅠ）和R-Z Monte Carlo模拟算法程序（R-Z MCSP），并对微观组织结构演变过程进行了模拟。结果表明，H-F Monte Carlo模拟算法的模拟效率明显高于R-Z Monte Carlo模拟算法的模拟效率。当晶粒取向Q值为90、150或200时，可有效消除晶粒粗化现象，当晶粒取向Q值为200和晶格点阵尺度为500×500时，具有良好的模拟效果。建立了两相陶瓷刀具材料微观组织结构演变的Monte Carlo Ports模型，该模型考虑了材料体系的晶界能和两相材料之间的相互扩散。创新性地采用具有一定的初始平均晶粒半径的仿真区域作为模拟烧结过程微观组织结构演变模拟的初始组织，利用开发的H-F MCSPⅡ模拟程序，考虑材料体系中晶界能比例、初始粉末形状及含量对模拟结果的影响，在规则单元和非规则单元的条件下模拟了烧结过程中两相陶瓷刀具材料微观组织结构的演变。结果表明，具有相同晶界能的基体相之间，较易扩散，晶粒生长快；第二相颗粒对基体相晶粒生长具有阻碍作用，第二相含量越大，对基体相晶粒生长的阻碍作用越强；两相之间的晶界能增大时，第二相对基体相晶粒生长的阻碍作用减弱。采用非规则单元模拟的微观组织结构更接近实验烧结时陶瓷刀具材料的微观组织结构形貌。建立了烧结过程中含有气孔、液相和烧结助剂时陶瓷刀具材料微观组织结构演变的Monte Carlo Potts模型，在开发的H-F MCSPⅠ和H-F MCSPⅡ的基础上，对含有气孔、液相和烧结助剂时陶瓷刀具材料微观组织结构演变进行了模拟。结果表明，单相和两相陶瓷刀具材料致密度随模拟时间的变化趋势及两种刀具材料的致密度基本相同，两相陶瓷刀具材料的平均晶粒半径始终低于单相材料的，液相的存在可以促进致密化过程。烧结助剂对基体相晶粒的生长具有较强的钉扎作用，明显阻碍晶粒的生长。在相同的模拟时间内，不含气孔时刀具材料模拟的平均晶粒半径大于含有气孔时刀具材料的平均晶粒半径。平均晶粒半径均随模拟时间的增加而增大。建立了模拟时间和实际保温时间之间的关系模型，建立了烧结温度、烧结压力和微观组织结构演变之间的关系，并将其耦合到模拟程序中，实现了考虑烧结工艺参数时烧结过程中陶瓷刀具材料微观组织结构演变的模拟。结果表明，模拟后的陶瓷刀具材料平均晶粒半径随模拟时间的增加而增大，利用温度因子法模拟的平均晶粒半径随温度升高而增大，模拟的平均晶粒半径随压力的升高而增大，但是烧结压力对晶粒生长的影响程度小于烧结温度的影响，这与实际实验结果基本吻合，证明了模型的正确性。在考虑气孔、液相和烧结助剂的条件下，模拟了烧结过程中单相和两相Al₂O₃基陶瓷刀具材料微观组织结构的演变，并进行了实验验证。结果表明，单相和两相Al₂O₃基陶瓷刀具材料平均晶粒直径的模拟值略低于实测值，其主要原因是将MgO作为惰性粒子，仅考虑了其钉扎作用，忽略了液相引起的颗粒重排问题，假设模拟前的粉末之间存在晶界能，仅考虑晶界扩散而忽略了其它扩散方式等。刀具材料平均晶粒直径的模拟值和实测值之间的误差率仅为12.1-18.2％，可认为具有较高的模拟精度，证明了模拟方法的正确性，为设计陶瓷刀具材料、优化烧结工艺参数和刀具力学性能奠定了基础。更多还原

【Abstract】 The advanced ceramic tools have been one of the most important cutting tools applied in high efficiency and precision machining because of its high hardness, good wear resistance and elevated-temperature anti-oxidation. However, the fracture toughness of ceramic tools is low at the present time and the mechanical properties of ceramic tools are governed by its microstructure. In order to provide the theory guide for the improvement in the fracture toughness, it is very significant to simulate and optimize the microstructure of ceramic tool materials.The microstructure evolution for the ceramic tool materials during fabrication has been simulated with the Monte Carlo Potts model. The novel H-F Monte Carlo simulation algorithm is proposed based on the systemic research of the present Monte Carlo Potts simulation algorithm and verified by experiments.In the H-F Monte Carlo simulation algorithm, a grain lattice is randomly chosen in simulation space firstly, and then the grain lattice which lies in the grain boundary is used to attempt another reorientation. So, the H-F Monte Carlo simulation algorithm has more efficiency than the present Monte Carlo simulation algorithm. The H-F MCSPI and R-Z MCSP software have developed with Visual C++ compiler and C++ program language on the base of H-F Monte Carlo algorithm and R-Z Monte Carlo algorithm respectively. The microstructure evolution has been simulated with the H-F MCSPI and R-Z MCSP. The simulation efficiency of H-F Monte Carlo algorithm is remarkably higher than that of R-Z Monte Carlo algorithm. The grain coarsening effect is eliminated when the grain orientation value Q is equal to 90, 150 and 200 respectively. The satisfying simulation results can be gained when the grain orientation Q and the lattice size space are 200 and 500 X 500 respectively.The Monte Carlo Potts model for simulating the microstructure evolution of the two-phase ceramic tool materials has been established. The model contains all boundary energy in the material system and the diffusion between the matrix and the second-phase material. The simulation space with the initial grain radius is adopted creatively at the beginning of the simulation for the microstructure evolution during the fabrication of the ceramic tool materials. The microstructure evolution of two-phase ceramic tool materials is simulated under the regular and irregular cell condition with the developed H-F MCSPII simulation software. At the same time, the proportion of grain boundary energy, the initial shape of powders and contents are considered. It is shown that the matrix which has the same grain boundary energy diffuses easily each other, and the grain grows fast. The second particles can inhibit the matrix grain from growing, and the inhibitation function increases with an increment in the content of second particles. However, the inhibitation by second phase particles decreases with an increment in the boundary energy between the matrix and the second phase. The simulated microstruture that adopts the irregular cell is more similar with that of the real ceramic tool materials than the simulated microstruture that adopts the regular cell.The Monte Carlo Potts model, which can simulate the microstructure evolution for the ceramic tool materials containing pores, liquid phase and additives during fabrication, has been established. The microstructure evolution for the ceramic tool materials containing pores, liquid phase and additives during fabrication is simulated on the base of the developed H-F MCSPI and H-F MCSPII simulation software. It is shown that both the change trend of the densification with the simulation time and the densification of the single- and two-phase ceramic tool materials during fabrication is similar. The mean grain radius of the two-phase ceramic tool materials is always lower than that of the single-phase ceramic tool materials. The liquid phase benefits the densification during fabrication. The additives pin the grain growth strongly and impede the grain growth significantly. At the same simulation time, the simulated mean grain radius without the pores is larger than that with the pores. The mean grain radius increases with an increment in the simulation time.The relationship between simulation time and real duration time is established. The relationship between fabrication temperature and the microstructure evolution and relationship between fabrication pressure and the microstructure evolution are also established and incorporated into the simulation program. The microstructure evolution of ceramic tool materials is simulated with the fabrication parameters during the fabrication. The simulated mean grain radius increases with an increment in the simulation time. The simulated mean grain radius also increases with an increment in the fabrication temperature using the temperature factor. And the simulated mean grain radius increases with an increment in the fabrication pressure, however, the effect of the fabrication pressure on the grain growth is lower than that of the fabrication temperature. The simulation model is desirable because the simulation results with the fabrication parameters mentioned above are consistent with the practical experiment results.The microstructure evolution of single- and two-phase Al₂O₃ matrix ceramic tool materials is simulated under the simulation space containing pores, liquid phase and additives. The simulation results are verified. It is shown that the simulated mean grain diameter is slightly lower than the measured mean grain diameter, this is because that the MgO is treated as inert particles to pin the grain growth only, the rearrangement of particles caused by the liquid phase is omitted, the grain boundary energy is assumed to lie among the initial powders at the beginning of simulation, the grain boundary diffusion is only considered and other kinds of diffusions are neglected, etc. Because the error ratios of the simulated mean grain diameter and the measured mean grain diameter of ceramic tool materials are only from 12.1% to 18.2%, the simulation precision is high enough to be accepted. The simulation of the ceramic tool materials lays a foundation for designing the new ceramic tool materials and optimizing the fabrication parameters and mechanical properties of ceramic tool materials.更多还原