CalPhaD Coffee Lecture – CALPHAD-integrated Defect Thermodynamics

The history of CALPHAD is a history of making thermodynamics computationally useful with two pillars: Assessed descriptions of multi-component phases’ equilibria and their coupling with diffusion and phase transformations. This development invites a further step: extending the thermodynamic description from bulk phases to the defects within a microstructure.
Microstructure defects can adopt compositions and phase states that differ markedly from the surrounding bulk, yet these local states are rarely accessible through conventional phase diagrams. In this talk, I will present the CALPHAD-integrated density-based thermodynamic theory and phase-field framework (DPF). A coarse-grained description of atomic density connects the structural departure from the bulk to the local free energy, while retaining assessed CALPHAD thermodynamic information. Connections to atomistic structures and energetics will be discussed.
Applications illustrate what this extension adds to materials design, from grain boundary phase diagrams to co-segregation maps for chemically complex materials. We review successful applications in steels, Al alloys and other alloying systems. The outlook toward Assessing Microstructure Phase Maps, my ERC Consolidator Grant AMASE, will be presented. We discuss how defect thermodynamics can provide a foundation for the next generation of CALPHAD software and tools, connecting thermodynamic databases, atomistic information and microstructure simulation.