非常规烧结工艺中晶粒非等温合并的相场法模拟
Phase-field modeling of non-isothermal grain coalescence in the unconventional sintering techniques
摘要：
建立了一个非等温的相场模型，用于研究烧结过程中晶粒的非等温聚结，并对非平衡、高温度梯度的放电等离子烧结、场辅助烧结和选择性激光烧结等非常规烧结技术的模拟具有潜在的应用价值。在模型中，采用序参量来描述体相和大气/孔隙区，以及晶体学取向。在熵分析的基础上，得到了自由能量密度随温度变化的表达式，其中包含了由温度和序参量变化引起的内能和与序参量相关的构型熵的贡献.利用表面能、晶界能和界面宽度的实验数据，确定了与温度相关的模型参数。从热力学热力学定律出发，导出了序参量的动力学方程和序参量耦合的传热方程。该模型是通过有限元方法数值实现的。两个相同颗粒的晶粒合并表明，非等温条件导致不对称的形态和弯曲的晶界，由于在现场的表面和晶界能量梯度引起的局部温度不均匀性。对两个不同颗粒和多个颗粒的非等温晶粒聚结的更多模拟呈现了晶粒收缩/生长、颈部生长和孔隙度的时间演化，证明了模型的能力和通用性。预计这项工作可以为非常规烧结技术的研究社区做出贡献，该技术可用于模拟非等温相关的微观结构特征。
英文摘要：
A thermodynamically consistent phase-field model is developed to study the non-isothermal grain coalescence during the sintering process, with a potential application to the simulation in unconventional sintering techniques, e.g. spark plasma sintering, field-assisted sintering, and selective laser sintering, where non-equilibrium and high temperature gradient exist. In the model, order parameters are adopted to represent the bulk and atmosphere/pore region, as well as the crystallographic orientations. Based on the entropy analysis, the temperature-dependent free energy density is developed, which includes contributions from the internal energy (induced by the change of temperature and order parameters) and the order parameter related configurational entropy. The temperature-dependent model parameters are determined by using the experimental data of surface and grain boundary energies and interface width. From laws of thermodynamics, the kinetics for the order parameters and the order-parameter-coupled heat transfer are derived. The model is numerically implemented by the finite element method. Grain coalescence from two identical particles shows that non-isothermal condition leads to the unsymmetric morphology and curved grain boundary due to the gradients of on-site surface and grain-boundary energies induced by the local temperature inhomogeneity. More simulations on the non-isothermal grain coalescence from two non-identical and multiple particles present the temporal evolution of grain shrinkage/growth, neck growth, and porosity, demonstrating the capability and versatility of the model. It is anticipated that the work could provide a contribution to the research community of unconventional sintering techniques that can be used to model the non-isothermal related microstructural features.
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