Pulsed Metallurgy for 2-Dimensional Structuring of Metallic Thin Films and Surfaces

• Applicant: Dr.-Ing. Karsten Woll
• Subject Area: Metallurgical, Thermal and Thermomechanical Treatment of Materials ; Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: from 2016 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 325754192

The combination of maximal strength and deformability serves as guidance for the development of future metallic materials. However, the realization is very challenging because strength and ductility/toughness are conflicting properties. It has been widely recognized that microstructure design is crucial for solving this conflict. The Emmy-Noether-Group considers this as motivation and is developing “pulsed metallurgy” as a tool for microstructure design of metallic thin film composites. The current project develops pulsed metallurgy as a tool for thin film and surface structuring. Al/Ni multilayers are the model materials. They are globally heated while a structuring mask serves as heat sink. Structuring cavities in the mask locally impede heat flux through the mask which creates temperature hot-spots according to the cavity geometry. The quasi-steady-state of the structure geometry (temperature profile) in the thin film is one advantage of this approach enabling us to utilize the kinetic of the metallurgical phenomena (grain growth and phase transformations) in a wider temporal range. The microstructure could be tuned in a broader spectrum. Due to potential effects of the substrate and the mask on the phase transformations, it cannot be assumed that the microstructure development in the hot spots follows the current knowledge of pulsed metallurgy. In particular, the high cooling rates > 10, 000 K/s during quenching are crucial in this respect. Hence, the current proposal explores phase transformations in Al/Ni multilayers under the hot spot’s thermal history. In addition, structuring precision is a second topic of the project. The measurement of the temporal evolution of the hot spot’s temperature is very challenging. Thus, a method will be developed allowing us to thermally analyze the phase transformations under the conditions of the hot spot. In detail, results of a model structuring experiment will be correlated with those of a model analyzing experiment. Both base on temporal variations in the electrical resistance either during structuring or the resistive heating of the samples in thin film heaters. Phase transformations create peaks in the resistance derivative in both the experiments. Heating rate variations will be used to adjust the temporal peak position to generate similar thermal histories in both the experiments. Eventually, this correlation paves the way to explore phase transformations in thin films in the analyzing experiment under the thermal conditions of the hot spot. Supporting transmission electron microscope studies are used to investigate potential effects of the phase transformations localization in the microstructure. To reveal mechanically interesting structuring conditions nanodindentation experiments will be performed. Finally, the combination of thermal analysis, microstructure evaluation and determination of mechanical properties creates a basis to reveal first microstructure- property-relationships.

• DFG Programme: Independent Junior Research Groups