Scale-bridging phase-field simulations of microstructure responses on nucleation in metals and colloids

从原子到介观尺度的相场模拟被用来分析金属和胶体体系中非均相成核的微结构响应。通过结合分子动力学(MD)和相场(PF)模拟或通过混合相场模拟，实现了金属中从1 nm到10μm的尺度桥接。三维数值计算的关键是采用性能优化的模拟技术和自适应网格。Ni、Ni-Cu、Ti、Al-Cu、Al-Ni和Al-Ti的热力学参数由实验测量和协同基团的分子动力学模拟得到。在PF模拟中，系统地研究了微结构对参数集、核形状和衬底特性的响应。对微观结构形成的大尺度模拟与实验观测进行了比较。扩展的PF模型涵盖了一种方法，包括体积约束、线张力能量公式和衬底表面的特定边界条件。将新模型应用于固着液滴的模拟，以精确地分析平衡形状和扩散过程。特别地，利用高阶势的形式研究了线张力对三维三线杨氏力平衡的长度尺度效应。在最近设计的PF晶体模型的基础上，提出了一种新的硬球胶体体系的PF模型。Ginzburg-Landau泛函将从动力学密度泛函理论(DDFT)中推导出来，其中考虑了从福尔瓦通量采样(FFS)中识别相关序参数的结果。

Phase-field simulations from atomic to mesoscopic length scales are used to analyse the microstructure responses on heterogeneous nucleation, both in metallic as well as in colloidal systems. The scale-bridging from 1 nm to 10 μm in metals is achieved either by combining Molecular Dynamics (MD) and Phase-field (PF) simulations or by hybrid PF modelling. Essential for three dimensional numerical computations is the employment of performance optimized simulation techniques and adaptive grids. Thermodynamic parameters for Ni, Ni-Cu, Ti, Al-Cu, Al-Ni and Al-Ti are provided from experimental measurements as well as from MD simulations of cooperating groups. The microstructure responses on the parameter sets, on the shape of the nuclei and on the characteristic properties of the substrate are systematically investigated in PF simulations. Large-scale simulations of microstructure formations are compared with experimental observations. Extensions of the PF model cover a method to incorporate volume constraints, a line tension energy formulation and specific boundary conditions at the surface of the substrate. The new model is applied to sessile drop simulations to precisely analyse equilibrium shapes and diffusion processes. In particular, the formalism with higher order potentials is used to investigate the length-scale dependent effect of the line tension on the Young’s force balance at triple lines in 3D. A new PF model for colloidal systems of hard spheres will be formulated on the basis of the recently designed PF crystal model. The Ginzburg-Landau functional will be derived from Dynamical Density Functional Theory (DDFT) taking the results from identification of the order parameter of relevance from Forware Flux Sampling (FFS) into account.