Three-Dimensional Modeling of Microstructural Characteristics in the Initial Stage of Liquid Phase

• Main Authors: LIU PO LIANG, 劉柏良
• Other Authors: LIN SHUN TIAN
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/13196970584784781721

博士 === 國立臺灣科技大學 === 機械工程系 === 90 === A complex geometry of a powder compact in a three-dimensional multiple particle arrangement was generated by a Monte Carlo method, and the microstructural characteristics of liquid phase sintered systems in the initial stage was solved by a numerical computation. With this probability model, irregular packing of particles in a three-dimensional space could be formulated with the variations of particle size and particle size distribution. Unlike two-dimensional analytical models where the grain boundary energy was a constant value, a relationship between the grain boundary energy and the misorientation angle between neighboring grains could be incorporated into the model in a probability manner. Thus, the dihedral angle between neighboring grains and liquid phase could be determined, and the contiguity of the solid phase and the dihedral angle between solid and liquid phases could be calculated. The effect on contiguity of adding doped materials was also quantified and related to the energy-misorientation relationship. The high degree of grain boundary penetration by liquid film was found to be a result of excessive probability satisfying a necessary condition for wetting, 2rsl<=rGB. Consequently, the coordination number decreases with the high probability for wetting. Therefore, the contiguity for a given solid volume fraction was decreased with the increase of the solid-liquid interface area. All specimens show a strong correlation between the contiguity C and coordination number N , irrespective of the width of the grain boundary energy cusp at the special misorientation or of the value of 2rsl/rRGB. The correlation can be expressed as:N/No=Cn/Co, where No is the mean coordination number, Co is the mean contiguity, and Cn is the mean contiguity having the coordination number N. The K value distributions of liquid phase sintered systems, parameters linked the two-dimensional connectivity to the three-dimensional coordination number, were also solved by the numerical computation. Simulation results indicate that the mean K value in the initial stage of liquid phase sintering increases with an increasing volume fraction of liquid, an increasing ratio of the mean base particle size to the mean additive particle size, and a decreasing standard deviation of the particle size distribution. These findings of the simulation are favorably compared with past experimental observations on Fe-Cu-C or W-Ni-Fe alloys. Furthermore, this model was developed to simulate three-dimensional grain characteristics in the initial stage of liquid phase sintering. Simulated grains, including a cluster of bonded particles, were treated in this three-dimensional multi-particle arrangement of the powder compact, and each cluster was assumed to be coalesced to reduce the system energy. Simulation results indicate that the grain size distribution in the initial stage of liquid phase sintering broadens with an increasing wetting angle, increasing ratio of the mean base particle size to the mean additive particle size, and increasing standard deviation of the particle size distribution. The grain profile was also observed in this study.