Crystal growth velocity in deeply undercooled melts of glass forming Zr-based alloys

• Applicants: Professor Dr. Dieter M. Herlach (†); Professorin Dr. Britta Nestler
• Subject Area: Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials ; Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: from 2013 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 238485687

The corporate goal is to investigate the solidification of glass-forming materials through both, experiments and phase-field simulations. At higher undercoolings, diffusion gets limited in materials forming glasses. This leads to a non-monotonic behavior of the velocity as a function of undercooling. To understand this, we consider Zr-based alloys as they can be cooled in the vicinity of the glass transition temperature in a levitation setup. We treat both, binary and multi-component alloys, and establish the solidification paths and kinetics. The experimentalists evaluate composition profiles as well as the crystal growth velocities at different undercoolings and provide the data for validation of the developed quantitative phase-field model for solidifications at higher undercoolings involving effects of solute trapping and partitionless phase transition. The phase-field model is further used to investigate pattern formations in glass-forming systems and to characterize the morphologies obtained at different undercoolings. The observed microstructures and velocity-undercooling relations are correlated to those for non-glass forming materials and the differences will be theoretically researched. The geometrical characteristics of the microstructures, such as dendritic tip radii and eutectic lamellae spacings are compared with experiments and with analytical theories, the corresponding discrepancies are analyzed and appropriate corrections to the theoretical models for glass forming materials are discussed. We study morphological transitions from dendritic to eutectic microstructures and determine the onset of these transitions as a function of undercooling and off-eutectic compositions. The overall aim is to explore the kinetics, solidification and topology paths of glass forming alloys under extreme conditions.

• DFG Programme: Research Grants