Study of ternary eutectic microstructures using 3D phase-field simulations and directional solidification experiments of Al-Ag-Cu

三相共晶的三维微观结构演化包含了多种形态，但人们对这些形态的理解还很不清楚，尤其是对各种规则和不规则结构出现的条件还不清楚。其目的是通过适当结合三维相场建模和针对选定范围的速度跳跃和成分的专用实验，在理解Al-Ag-Cu中的微观结构形成方面取得实质性进展。该合作项目的一个特别重点是共同开发一个综合后处理框架，通过实施适当的编程接口和应用相同的工具来表征模拟和实验3D微结构。KIT的团队将采用在第一个资助期内开发的新的定量相场模型和性能改进的模拟方法，深入了解砖结构、两相棒、螺旋和耦合生长等3D微观结构的形成。在相场模型中加入了Al-Ag-Cu的热力学数据。与科隆的实验相协调，我们的目标是系统地改变施加的拉速跳跃和合金成分，并分析所得的浓度分布和微观结构特性，如形态类型，相分数，间距和表面积。基于代码的并行性，将对高性能集群进行3D模拟研究，并能够导出形态转变图和微观结构特征与凝固条件之间的相关函数。德国航天中心的研究小组将使用所谓的ARTEMIS设施进行定向凝固实验，ARTEMIS设施是一种基于气凝胶的熔炉，由于使用了二氧化硅气凝胶，因此可以控制平坦的固液界面，凝固速度和界面前的温度梯度。实验将在0.1 μ m/s至5 μ m/s的速度范围内进行，温度梯度为3 K/mm。微观结构的演变将与新开发的方法，如最近邻（NN）的概率，NN距离为不同的阶段，平均相颗粒面积和颗粒数密度进行分析。除了光学显微镜，我们将使用扫描电镜与EDX和EBSD的局部和全球组成的变化，相组成的测定，和局部取向的阶段。一些样品将使用第一阶段建立的X射线断层扫描进行3D分析。我们计划应用BESSY、DESY和ESRF等外部测量能力。

The microstructure evolution of three-phase eutectics in 3D contains a broad variety of morphologies and is by no means understood, especially not the conditions for the occurrence of the various regular and irregular structures. The aim is to achieve substantial progress in understanding the microstructure formation in Al-Ag-Cu by a suitable combination of 3D phase-field modeling and dedicated experiments for a selected range of velocity jumps and compositions. A particular focus of the collaborative project is a mutual development of an integrated postprocessing framework to characterize simulated and experimental 3D microstructures by implementing appropriate programming interfaces and by applying identical tools. On the basis of the joint framework, the simulation results will be compared with experimental photographs and measured structural quantities.The team at KIT will employ a new quantitative phase-field model and performance improved simulation method developed in the first funding period to get insight into 3D microstructure formation such as brick structures, two phase rods, spirals and coupled growth. A thermodynamical data set of Al-Ag-Cu is incorporated in the phase-field model. In coordination with the experiments in Cologne, we aim to systematically vary the imposed pulling velocity jumps and alloy composition and analyze the resulting concentration profiles and microstructural properties such as morphology type, phase fraction, spacing and surface area. Based on the parallel nature of the code, 3D simulation studies will be carried out on high performance clusters and enable to derive morphology transition diagrams and correlation functions between the microstructure characteristics and solidification conditions. A particular focus will be the investigation of the effect of solid-solid anisotropy on the pattern formation and morphological pathways.The team at DLR will perform directional solidification experiments using the so-called ARTEMIS facilities, aerogel based furnaces which, due to the utilization of silica-aerogels, control a flat solid-liquid interface, the solidification velocity and the temperature gradient ahead of the interface over the processing length. The experiments will be performed in a velocity range of 0.1 mu m/s to 5 mu m/s with a temperature gradient of 3 K/mm. The microstructure evolution will be analyzed with newly developed methods such as nearest neighbor (NN) probabilities, NN distances for the different phases, average phase particle areas, and particle number densities. Besides light microscopy, we will use SEM with EDX and EBSD for local and global composition variations, determination of phase compositions, and local orientation of the phases. Some of the samples will be analyzed in 3D using x-ray tomography as established in the first period. We plan to apply external measurement capabilities like those at BESSY, DESY and ESRF.