Density-based Thermodynamic Model and Open-Source Software for Quantitative Description of Interfacial Phase Behavior in Multi-Phase Multi-Component Alloy Systems

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Knowledge-based design of engineering alloys requires quantitative thermodynamic descriptions of each and all elements of microstructure, from primary bulk phase and secondary-phase precipitates to microstructure defects, e.g., grain boundaries and phase boundaries. While thermodynamics of bulk phases are well established and steadily developing, thermodynamic descriptions and databases for the microstructure defects are far less explored. In this project, we will develop a robust framework for computing thermodynamic databases and phase diagrams for interfacial microstructure defects based on available bulk thermodynamic data. We will develop a generalized multi-phase, multi-component density-based model enhanced with elastic energy considerations (for interstitial atoms) and a heterogeneous nucleation model to address defects engineering in multi-phase multi-component alloy systems. Coupled with these theoretical developments, an open-source software package for computing defects’ thermodynamics and kinetics will be developed. The ultimate open-source software will use available CALPHAD-based bulk thermodynamic databases as inputs and compute thermodynamic properties, phase diagrams and their temporal evolution of the interfacial defects. The applications of our generalized model and the software package will be examined by studying grain boundary precipitation and the formation of precipitate-free zones in several trending aluminum alloys. By studying a wide range of composition and temperature spaces, we will construct a systematic relationship between alloy nominal composition and thermomechanical treatments of various Al alloys with their interfacial phase changes. Strategies for alloy and processing designs will be proposed to mitigate interfacial failure in aluminum alloys. Along with the increasingly advancing researches on defects engineering, the current project aims at a break-through development in computational thermodynamics of the microstructure defects. The generalized density-based model and software will provide powerful tools to address the emerging needs in quantifying the phase behavior of microstructure defects. The outputs of the software can guide knowledge-based engineering of interfacial defects and provide CALPHAD-compatible databases, necessary for data-driven approaches to microstructure design.