Multiscale modeling based on phase-field approaches: consistency analysis regarding growth and melting kinetics in metals

• Applicant: Dr. Mohammed Guerdane, Ph.D.
• Subject Area: Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials
• Term: from 2012 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 214287316

The project deals with one of the central challenges in multiscale modeling, namely how to bridge the gap among atomistic and macroscopic approaches in order to ensure that the descriptions at all levels are quantitatively consistent with each other. This task is carried out for one of the promising multiscale methods: The hierarchical coupling approach that combines molecular dynamics (MD) with phase-field (PF) simulations. The consistency analysis is achieved by detailed comparisons of quantitative predictions of the considered modeling methods for the growth and melting kinetics. The latter are typical multiscale problems in material physics. The MD simulations provide the physical quantities needed for the construction of the multiscale models. Of central importance are the bulk free energy and the solid-liquid interfacial free energy whose calculation requires the use of special methods. The monatomic and binary systems to be investigated are Fe, Al, NiZr and NiAl, for which reliable potentials are available in the literature. The first project period led to essential findings concerning, in particular, the diffusion at the solid-liquid interface, the interfacial thickness anisotropy, and their determining influence on the growth and melting kinetics. These insights resulted in improvements of the design of the phenomenological PF model leading to enhancements of the prediction accuracy of the MD/PF coupling. The second project period is aimed at understanding the apparent correlation between these insights and establishing them in quantitative laws and possible universal behaviour. In particular, we analyze the temperature dependence and anisotropy of the correlation length over which the crystal affects the liquid diffusion. The underlying dynamical anisotropy is expected to be connected with the structural interface-thickness anisotropy, a concept that we demonstrated for bcc Iron in the first project period. A generalization of this anisotropy concept to fcc metals and alloys will be here investigated and its reliability assessed by linking MD to PF modeling. Understanding the different structural and dynamical interface anisotropies is a prerequisit to accurately predict the dynamics of interface morphologies like dendrites and eutectics. In the light of the gained insights, we revisit some classical growth models in an attempt to rationalize their failings to describe crystallization behaviour in alloys.

• DFG Programme: Research Grants