Decoding Grain Growth: Disconnection Motion and the Role of Solutes

• Applicants: Dr.-Ing. Jules Dake; Professor Dr. Marco Salvalaglio
• Subject Area: Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials ; Computer-Aided Design of Materials and Simulation of Materials Behaviour from Atomic to Microscopic Scale
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 570666382

Grain boundary (GB) migration is a fundamental process by which the microstructure of a crystalline material evolves. Thermally activated GB migration gives rise to grain growth, which, owing to the impact of grain size on materials properties, has been the focus of intensive study for over a century. Conventional models assert that curved GBs always migrate toward their center of curvature and that solute atoms, whether deliberately added or present as impurities, invariably impede GB migration. However, recent simulations and experimental observations have called these long-held assumptions into question. Although GBs are defined as the interfaces between adjacent grains of differing crystallographic orientation, they are often treated as smooth continuum surfaces—an approach that neglects their underlying atomic structure. Accounting for this structure reveals that curved GBs necessarily contain surface steps or ledges, which form one-dimensional defects known as disconnections. The concept of disconnections is not new—it has been used to explain GB shear coupling for decades—but its broader application to general GB migration is relatively recent. If GB migration is indeed governed by the motion of disconnections, this framework could provide a unified explanation for a wide range of heretofore perplexing results, such as the extremely large scatter in measured GB mobility values, the stagnation of grain growth, and even instances of solute acceleration, where solute atoms unexpectedly speed up GB migration. The central goal of this research project is to develop physical models for GB migration that consider the constraints inherent to real polycrystals: specifically, the interconnected nature of the GB network and the unavoidable presence of solute atoms at and near GBs. To date, most investigations of disconnection-mediated GB migration have focused on bicrystals with flat GBs or on selected GBs in extremely thin, nanocrystalline samples. In bulk polycrystals, we hypothesize that disconnection motion is constrained by the configuration and chemistry of GBs across multiple microstructural length scales. These constraints can lead to stress buildup, which in turn has a profound effect on local GB velocities. To isolate the effects of individual constraints, we will deliberately alter geometric boundary conditions by selectively removing them—either with laser ablation or the addition of a liquid phase—and we will investigate disconnection-solute interactions through dedicated experiments and scale-bridging simulations that span atomistic to mesoscale regimes. Finally, we will develop state-of-the-art algorithms to simulate grain growth under realistic conditions, incorporating geometric constraints and disconnection-solute interactions to model GB velocities. These simulations will serve as a “digital twin” for microstructure evolution, bridging the gap between theory and experiment.

• DFG Programme: Research Grants
• International Connection: Austria
• Partner Organisation: Fonds zur Förderung der wissenschaftlichen Forschung (FWF)
• Co-Investigator: Professor Carl Emil Krill III, Ph.D.
• Cooperation Partners: Oliver Renk, Ph.D.; Professor Dr. Lorenz Romaner; Dr. Daniel Scheiber