Hume-Rothery Symposium: Thermodynamics, Phase Equilibria and Kinetics for Materials Design and Engineering: CALPHAD Future Directions
Sponsored by: TMS Structural Materials Division, TMS: Alloy Phases Committee, TMS: Integrated Computational Materials Engineering Committee
Program Organizers: Carelyn Campbell, National Institute of Standards and Technology; Michael Gao, National Energy Technology Laboratory; Wei Xiong, University of Pittsburgh
Tuesday 2:00 PM
February 25, 2020
Room: 32A
Location: San Diego Convention Ctr
Session Chair: Fan Zhang, CompuTherm LLC; Peisheng Wang, Central South University
2:00 PM Invited
Thermodynamics at Equilibrium and Non-equilibrium – Genomic Tools for Materials Design: John Agren1; 1Royal Institute of Technology
CALPHAD style modelling is now generally accepted as one of the most powerful tools in materials engineering. It constitutes a major part of the Materials Genome, i.e. the combination of computational tools and databases that serve as a basis for materials design. In the talk it is reviewed how data representing equilibrium thermodynamics may be applied to non-equilibrium processing. In the CALPHAD method the measured thermodynamic properties are represented by models, yielding mathematical functions that may be extrapolated far outside the equilibrium range. The talk will discuss examples involving highly undercooled liquids and precipitation/dissolution of secondary particles under non-equilibrium conditions.A major and critical part when building a CALPHAD representation of a materials system is the assessment procedure which will be discussed. This is an area where Ursula Kattner and her coworkers at NIST have played a leading role internationally.
2:40 PM Invited
Phase Equilibria and Interfacial Migration in Stressed Solids: Nicholas Weadock1; Peter Voorhees2; Brent Fultz1; 1California Institute of Technology; 2Northwestern University
A possible route to storing hydrogen for hydrogen-based energy systems is via hydride formation. One challenge of using metal hydrides to store hydrogen is an efficiency loss due to hysteresis: the absorption and desorption of hydrogen does not occur at the same hydrogen gas pressure. We examine phase formation and phase equilibria in the hydrogen-palladium system where a significant difference in lattice parameters between the hydride and matrix phases generates stress in the system. The stress is thought to lead to a coherent phase equilibrium state that induces the hysteresis. However, experiment shows that the hysteresis is present even in a partially transformed system, indicating that a stress-induced jump in volume fraction of hydride is not responsible for the hysteresis. An explanation for the hysteresis that is based upon the driving force for interface migration in a stressed solid will be presented.
3:20 PM Invited
Interaction of Moving Grain Boundaries with Solutes in Alloys: Yuri Mishin1; 1George Mason University
Solutes in alloys can strongly interact with moving grain boundaries (GBs) and change their thermodynamic and kinetic properties. We apply a discrete model and a regular solution approximation to study the solute drag effect and the impact of GB motion on GB phase transformations. The model predicts all thermodynamic and kinetic properties of the moving GB, the GB phase diagram, and the solute drag force. Analysis shows that GB motion strongly affects the relative stability of GB phases and can even stabilize phases that are absolutely unstable under equilibrium conditions. In the steady-state regime, the GB phase diagram can be expanded by adding the GB speed play as another state variable. GB phase transformations are accompanied by drastic changes in GB mobility. The results are analyzed in the context of non-equilibrium thermodynamics. Results predicted by the model are compared with atomistic computer simulations of solute-boundary interactions.
4:00 PM Break
4:20 PM Invited
Computational Thermodynamics in Microstructure Modelling and Beyond: Georg Schmitz1; 1Access E V
Current methods and trends aiming towards “engineering the material” and their integration into the holistic framework of Integrated Computational Materials Engineering “ICME” will be highlighted. The somehow historical overview starts from the nascent stages of computational thermodynamics and continues via spatially resolved thermodynamics and kinetics in multi-phase-fields modes allowing the description of microstructure evolution in complex alloy systems. The journey further continues by highlighting methods to extract effective properties from microstructures and making them available to the FEM community, which typically focuses on “engineering with materials” and is interested in a number of parameters characterizing the properties of a material essentially without considering any influences of the materials microstructure. A major challenge in combining all these tools is to achieve their interoperability. The presentation thus concludes with a short introduction into the European Materials & Modelling ontology EMMO.
5:00 PM Invited
How Can the CALPHAD Method Do Better?: Zi-Kui Liu1; 1Pennsylvania State University
The CALPHAD (CALculation of PHAse Diagram) method based on modeling the properties of individual phases is foundational for Integrated Computational Materials Engineering (ICME) and enables computational materials design. In last two decades or so, the CALPHAD modeling has benefited significantly from the thermochemical data predicted from first-principles calculations, which not only supplement the lack of experimental data, but also provide data that cannot be directly measured experimentally such as energetics in individual sublattices of a phase with multiple sublattices (J. Phase Equilib. Diffus., 2009;30:517). The ESPEI code takes advantage of this set of data and provides a fast approach to evaluate properties of individual phases (MRS Commun. 2019;9:618). Even though the CALPHAD method can model both stable and unstable equilibria such as spinodal in multi-component systems, there are some remaining challenges that will be discussed in the presentation along with potential directions to further develop the CALPHAD method.