A New Method to Efficiently and Reliably Measure Ternary Diffusion Coefficients

非技术总结：扩散系数是衡量原子在不同温度下跳跃的速度和不同元素（原子）之间混合的速度，因此它们是材料工程师设计新材料时需要的一些最基本的材料特性，以增强性能，从而提高许多设备的效率和降低排放。例如，扩散系数决定了喷气发动机涡轮叶片在高温下高速旋转时的伸长程度（一种称为蠕变的现象）。人们已经开发出测量两种元素（二元体系）之间扩散系数的有效方法，但没有有效的方法来测量三种元素（三元体系）之间的混合速度。本研究旨在开发一种革命性的方法来加快三元体系扩散系数的测量。这种新的高通量三元扩散测量方法和算法的广泛应用将导致更多的数据来建立数据库，以加速更先进材料的设计，以提高美国制造业的竞争力。一名来自代表性不足群体的研究生将在本项目的支持下获得博士学位。我们还将聘请两名来自不同背景的本科生研究助理参与这个项目，以激发他们对结构金属的兴趣，并让他们获得研究经验。技术概述：除了二元扩散系数外，三元扩散系数对于建立可靠的多组分系统扩散和迁移率数据库至关重要。每一组可靠的三元扩散系数（交叉项）通常是从两个独立的扩散偶（路径）的成分交点测量的，这导致效率很低。从单个扩散偶中提取三元扩散系数的方法会导致非常大的误差。本研究的目的是建立一种革命性的新方法，以前所未有的效率可靠地测量三元扩散系数，包括对交叉扩散项的严格评估。新的堆叠耦合扩散倍数（scdm）能够在三元组合空间中创建许多组合交叉点。正演模拟分析（FSA）从每个SCDM收集的众多成分剖面将允许在三元体系中广泛成分中提取可靠的三元扩散系数。从本质上讲，一个SCDM可以用来收集整个三元体系的可靠扩散系数。本研究将展示这种新方法，并使用Fe-Co-Ni三元体系对其进行验证，该体系具有可靠的扩散系数，可用于直接比较。Fe-Co-Ni-Cr-Cu体系是高熵合金（多主元素合金）的良好模型体系，在该体系内可得到10个三元体系丰富的新三元扩散系数。在本研究中，将开发具有相界面（例如bcc/fcc）的二维三元扩散模拟方法和算法，以实现多相三元体系中三元扩散系数的高效可靠提取。新方法将在测量可靠的三元扩散系数方面实现前所未有的效率，从而加速建立多组分扩散（迁移率）数据库，以精确模拟材料过程。准确的动力学模拟将有助于加速新材料的设计和加工优化，以提高美国制造业的竞争力。该方法还可以推广到系统有效地测量多组分（三元以上）系统的扩散系数。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARY:Diffusion coefficients are a measure of how fast atoms jump and the speed of intermixing between different elements (atoms) at various temperatures, thus they are some of the most fundamental materials properties that materials engineers need to design new materials for enhanced performance which can lead to higher efficiency and lower emissions for many devices. For instance, diffusion coefficients dictate how much a jet engine turbine blade would elongate at high temperatures during high speed rotation (a phenomenon called creep). Efficient methods have been developed to measure the diffusion coefficients between two elements (referred to as binary systems), but no efficient methods exist to measure the speed of intermixing among three elements (ternary systems). This study aims to develop a revolutionary method to speed up the measurements of diffusion coefficients of ternary systems. Wide application of this new high-throughput ternary diffusion measurement methodology and algorithms will lead to much more data to build databases to accelerate the design of more advanced materials to enhance US manufacturing competitiveness. One graduate student from an underrepresented group will be trained towards her/his PhD degree under the support of this project. Two undergraduate research assistants from diverse backgrounds will also be hired to work on this project to excite their interest in structural metals and to allow them to gain research experience.TECHNICAL SUMMARY: In addition to binary diffusion coefficients, ternary diffusion coefficients are essential to the establishment of reliable diffusion and mobility databases for multicomponent systems. Each set of reliable ternary diffusion coefficients (with cross terms) at one composition are usually measured from the composition intersection point of two separate diffusion couples (paths), which leads to very low efficiency. Approaches to extract ternary diffusion coefficients from a single diffusion couple can lead to very large errors. The objective of this study is to establish a revolutionary new methodology to reliably measure ternary diffusion coefficients at unprecedented efficiency, including rigorous evaluations of the cross diffusion terms. The new stacked-couple diffusion multiples (SCDMs) have the capability to create numerous composition intersection points across the ternary composition space. Forward simulation analysis (FSA) of numerous composition profiles collected from each SCDM will allow extraction of reliable ternary diffusion coefficients across wide compositions in ternary systems. In essence, one SCDM can be used to collect reliable ternary diffusion coefficients of entire ternary systems. This study will demonstrate this new methodology and validate it using the Fe-Co-Ni ternary system for which reliable diffusion coefficients are available for a direct comparison. Copious new ternary diffusion coefficients will then be obtained for 10 ternary systems inside the Fe-Co-Ni-Cr-Cu system that is a good model system for high entropy alloys (multi-principal element alloys). During this study, approaches and algorithms for 2-dimensional ternary diffusion simulations with the presence of phase interfaces (e.g. bcc/fcc) will be developed to enable efficient and reliable extraction of ternary diffusion coefficients in multi-phase ternary systems. The new methodology will enable unprecedented efficiency in measuring reliable ternary diffusion coefficients for accelerated establishment of multicomponent diffusion (mobility) databases for accurate simulation of materials processes. Accurate kinetic simulations will help accelerate new materials design and processing optimization to enhance the US manufacturing competitiveness. The methodology may also be extended to systematically and efficiently measure diffusion coefficients of multicomponent (beyond ternary) systems in the future.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.