Grain boundaries are one of the most important constituents of a polycrystalline material and play a crucial role in dictating the properties of a bulk material in service or under processing conditions. Bulk properties of a material like fatigue strength, corrosion, liquid metal embrittlement, and others strongly depend on grain boundary properties such as cohesive strength, energy, mobility, etc. These boundary properties in turn are governed by the structure and chemistry of a grain boundary. Furthermore, it has recently been realized that grain boundaries themselves can be described as interface-stabilized phases. We are just at the advent to utilize the phase character of grain boundaries as a material design element.
In the first part of this project, we are focusing on the atomic structure and phase transformation in special grain boundaries in aluminum by using dedicated transmission electron microscopy techniques in combination with the atomistic simulations. Epitaxial aluminum thin films are deposited on sapphire substrate by molecular beam epitaxy or other physical vapor deposition techniques to establish a template based methodology for obtaining specific grain boundary types. Electron backscatter diffraction measurements are employed to characterize the global grain boundary structure and types present in the films. Focused ion beam sample preparation allows then to extract specific grain boundaries for further atomic scale investigations of their structure, chemistry and transitions.
The second part of the project is focusing on in-situ TEM experiments to study the phase transformation behavior of the pre-characterized grain boundaries. The main objective is to develop unified correlations of the grain boundary structure, their transitions and properties.
Last, but not least, we will explore the influence of impurity elements on the structure and properties of grain boundaries and how they can be utilized to tailor the phase behavior of these interfaces.
International researcher team presents a novel microstructure design strategy for lean medium-manganese steels with optimized properties in the journal Science
In this project, we investigate a high angle grain boundary in elemental copper on the atomic scale which shows an alternating pattern of two different grain boundary phases. This work provides unprecedented views into the intrinsic mechanisms of GB phase transitions in simple elemental metals and opens entirely novel possibilities to kinetically engineer interfacial properties.
About 90% of all mechanical service failures are caused by fatigue. Avoiding fatigue failure requires addressing the wide knowledge gap regarding the micromechanical processes governing damage under cyclic loading, which may be fundamentally different from that under static loading. This is particularly true for deformation-induced martensitic…
Copper is widely used in micro- and nanoelectronics devices as interconnects and conductive layers due to good electric and mechanical properties. But especially the mechanical properties degrade significantly at elevated temperatures during operating conditions due to segregation of contamination elements to the grain boundaries where they cause…
The full potential of energy materials can only be exploited if the interplay between mechanics and chemistry at the interfaces is well known. This leads to more sustainable and efficient energy solutions.
In this project we work on correlative atomic structural and compositional investigations on Co and CoNi-based superalloys as a part of SFB/Transregio 103 project “Superalloy Single Crystals”. The task is to image the boron segregation at grain boundaries in the Co-9Al-9W-0.005B alloy.
This project deals with the phase quantification by nanoindentation and electron back scattered diffraction (EBSD), as well as a detailed analysis of the micromechanical compression behaviour, to understand deformation processes within an industrial produced complex bainitic microstructure.