A New Method to Efficiently and Reliably Measure Ternary Diffusion Coefficients

University Of Maryland, College Park, College Park MD

Investigators

Abstract

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.