A New Method to Efficiently and Reliably Measure Ternary Diffusion Coefficients

非技术摘要：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)之间混合速度的指标，因此它们是材料工程师设计新材料以提高性能所需的一些最基本的材料特性，从而为许多设备带来更高的效率和更低的排放。例如，扩散系数决定了喷气发动机涡轮叶片在高速旋转过程中在高温下会拉长多少(一种称为蠕变的现象)。已经开发了有效的方法来测量两种元素(称为二元系)之间的扩散系数，但还没有有效的方法来测量三种元素(三元系)之间的混合速度。这项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，以加速设计更先进的材料，以提高美国制造业的竞争力。在这一项目的支持下，来自代表性不足群体的一名研究生将接受攻读博士学位的培训。还将聘请两名来自不同背景的本科生研究助理参与这一项目，以激发他们对结构金属的兴趣，并使他们获得研究经验。技术摘要：除了二元扩散系数外，三元扩散系数对于建立多组分体系的可靠扩散和迁移率数据库至关重要。每组可靠的三元扩散系数(带有交叉项)通常是从两个独立扩散偶(路径)的组成交点测量的，这导致效率非常低。从单个扩散偶中提取三元扩散系数的方法可能会导致很大的误差。这项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)能够在三元组成空间中创建大量组成交点。正向模拟分析(FSA)从每个SCDM收集的大量成分分布将允许提取可靠的三元扩散系数在广泛的组成的三元系统。本质上，一个SCDM可以用来收集整个三元体系的可靠的三元扩散系数。这项研究将演示这一新的方法，并使用Fe-Co-Ni三元系统进行验证，该系统有可靠的扩散系数可供直接比较。Fe-Co-Ni-Cr-Cu系是研究高熵合金(多主元素合金)的良好模型体系，对10个三元系的扩散系数进行了研究。在这项研究中，将开发具有相界面(例如bcc/fcc)的二维三元扩散模拟的方法和算法，以便能够有效和可靠地提取多相三元体系中的三元扩散系数。新的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，以加速建立多组分扩散(迁移率)数据库，以便准确模拟材料过程。准确的动力学模拟将有助于加速新材料的设计和工艺优化，以提高美国制造业的竞争力。该方法未来还可以扩展到系统和有效地测量多组分(超越三元)系统的扩散系数。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.