Computational Modeling of Interdiffusion Microstructures

技术支持：近年来，无论是实验表征还是计算机模拟都揭示了许多现有理论和模型还不能完全解释的新现象。一个列表的例子包括相互扩散微观结构的分层，“角”在多相扩散路径，和特殊的点相图上，似乎作为“奇怪的吸引子”的扩散路径。标记的运动、0型边界和由柯肯德尔效应引起的沉淀物是可以添加到列表中的主题。此外，还有一些课题很少或根本没有受到关注，例如，偏离局部平衡条件对扩散路径的影响，沉淀粗化对相互扩散的影响，以及浓度梯度诱导漂流现象。这些现象为什么以及何时发生的不确定性阻碍了对设计师重要问题的回答。在这个更新项目中，一个正在进行的程序的分析，计算和实验的努力将被扩展到预测多组分，多相扩散偶的相互扩散微观结构。目标是定义多相系统中多组分扩散的科学原理，然后将其应用于使用扩散路径和相图等工具预测微观结构。为了模拟处于局部平衡且与沉淀物形态无关的现象，将使用DICTRA软件。然而，考虑到沉淀形态和过饱和（非平衡）的影响，并模拟含有一个以上的基质相的相互扩散微观结构，相场模型已经开发的PI将被扩展。扩展的模型将能够（a）包括沉淀物的成核的影响下，预先存在的微观结构和浓度梯度，（B）开发一种新的方法的基础上的Kim-Suzuki模型，以克服定量相场建模的内在长度尺度限制，和（c）占三相平衡。开发的分析和建模能力将通过精心设计的实验进行验证，并应用于开发对上述现象的基本理解。此外，它们将被应用于扩展在当前程序中提出的内氧化的新范例。非技术性：预测和理解互扩散微观结构的能力在高温加工和材料的广泛领域中具有许多应用，并且将是工艺和合金设计的未来进步的基础。该计划借鉴科学和技术的推力，以更好地了解多组分扩散，并设计更坚固的高温涂层和合金。为了使结果普遍可用，PI计划将其计算方法和实验及模拟结果放在一个开放的网站上，供学术界和工业界使用。特别是，一个自由的向下的二维（2D）相场开放源代码的扩散偶的任意微结构的Ni-Al-Cr系统的互扩散将提供。与此同时，PI将把知识、建模方法和软件程序整合到俄勒冈州立大学的本科和研究生课程中。特别是，一个新的研究生课程：扩散的分析和计算方法在多组分和多相系统将开发和一个新的模块应用DICTRA和相场软件程序来解决多组分和多相扩散问题将被引入到现有的本科课程材料建模（MSE 533）。

TECHNICAL: In recent years, both experimental characterization and computer simulations have revealed many new phenomena that are not yet fully explained by existing theories and models. A list of examples include demixing of interdiffusion microstructures, 'horns' in multiphase diffusion paths, and special points on phase diagram that seem to act as 'strange attractors' for diffusion paths. The motion of markers, Type-0 boundaries, and precipitates caused by the Kirkendall effect are topics that could be added to the list. In addition, there are topics that have received little or no attention, for example, the effect of deviations from local equilibrium conditions on diffusion paths, the effect of precipitate coarsening on interdiffusion, and the phenomenon of concentration-gradient induced rafting. Uncertainty about why and when these phenomena occur has hindered attempts to answer questions of importance to designers. In this renewal project, the analytical, computational and experimental efforts of an on-going program will be extended to predict interdiffusion microstructures in multi-component, multi-phase diffusion couples. The goal will be to define the scientific principles underlying multi-component diffusion in multi-phase systems and then to apply them to predicting microstructures using tools like diffusion paths and phase diagrams. To model phenomena that are in local equilibrium and independent of precipitate morphology DICTRA software will be used. However to account for the effects of precipitate morphology and supersaturation (non-equilibrium) and to model interdiffusion microstructures containing more than one matrix phase, the phase field models already developed by PIs will be extended. The extended models will be able (a) to include nucleation of precipitates under the influence of a pre-existing microstructure and concentration gradient, (b) to develop a new approach based on the Kim-Suzuki model to overcome the intrinsic length scale limit of quantitative phase field modeling, and (c) to account for three-phase equilibrium. The analytical and modeling capabilities developed will be validated against carefully designed experiments and applied to develop fundamental understanding of the aforementioned phenomena. Also they will be applied to extend the new paradigm of internal oxidation that was proposed in the current program. NON-TECHNICAL: The ability to predict and understand interdiffusion microstructures has many applications in the broad field of high temperature processing and materials and will be the foundation for future advances in process and alloy design. This program draws from scientific and technological thrusts to better understand multi-component diffusion and to design more robust high-temperature coatings and alloys. To make the results generally available, PIs plan to place their computational methods and experimental and simulation findings on an open web site for use by the academic and industrial communities. In particular, a free down-loadable two-dimensional (2D) phase field open source code for interdiffusion in diffusion couples of arbitrary microstructures for Ni-Al-Cr system will be provided. In the meantime, PIs will integrate the knowledge, modeling methods and software programs into undergraduate and graduate curricula at OSU. In particular, a new graduate course: Analytical and Computational Methods of Diffusion in Multi-Component and Multi-Phase Systems will be developed and a new module on applying DICTRA and phase field software programs to solve multi-component and multi-phase diffusion problems will be introduced to the existing undergraduate course on materials modeling (MSE533).