Dislocation-grain boundary interaction under tribological loading

• Applicant: Professor Dr. Christian Greiner
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 573672772

Single phase metallic, polycrystalline materials can be described as consisting of grain interiors and grain boundaries. To fundamentally understand the plastic behavior of metals under mechanical loading, dislocation motion within the grain interior, as well as the interactions between dislocations and grain boundaries, have to be understood. The fabrication of single crystals allowed researchers to uncover processes associated with the grain interior, such as differing hardening behavior depending on the crystallographic orientation of the grains. The significance of dislocation-grain boundary interactions on the mechanical behavior is also known for decades; see the Hall-Petch relationship. Today, both experimental and simulation-based approaches are providing insights into phenomena such as dislocation transfer or dislocation blocking at grain boundaries. However, many aspects remain unclear, and a comprehensive understanding of dislocation-grain boundary interactions has yet to be developed. This complexity arises from the vast variety of grain boundary characters and the small volume associated with grain boundaries. The approach of the present proposal is unique compared to many other studies on dislocation-grain boundary interactions, as we focus on a tribological loading scenario. We plan to use bicrystalline copper samples and systematically vary both the grain boundary character and the loading condition. Our experiments aim to gain insights into grain boundary displacement as well as into grain boundary step formation. Tribological loading offers the significant advantage of being able to sequentially load individual grains. This allows us to: a) identify where a specific dislocation originates from (with respect to the sliding direction), b) apply a high driving force to dislocations to overcome a grain boundary, and c) exploit the depth-dependent stress field under tribological loading to investigate the influence of varying plastic deformations on dislocation-grain boundary interactions. These aspects aim to provide a better general understanding of dislocation-grain boundary interactions, as well as from a purely tribological perspective, systematically studying the influence of grain boundaries. This is crucial, as essentially all tribologically loaded metallic components are polycrystalline. The knowledge generated through the implementation of this research on the long run is intended to be used to optimize tribological properties by tailoring the microstructure through the use of specific grain boundary types. This will contribute to creating more energy efficient tribological contacts.

• DFG Programme: Research Grants