In-situ and ex-situ characterisation of microstructure evolution in the scanning electron microscope for the development of microstructure models on the model material copper

• Applicant: Professor Dr.-Ing. Peter Starke
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 538560627

The understanding of microstructure evolution under quasi-static and cyclic loading of metallic materials is a central topic when it comes to coupling the mechanisms occurring in the material with the signal changes recorded via various measurement techniques. On the one hand, this results in a more fundamental understanding of damage development, and on the other hand, this information can be used as input variables in microstructure simulation models, whereby ideally a generally valid understanding of damage development that can be transferred to other materials can be established. The basic idea of the present project is to link the changes in measured variable signals with material mechanisms and to develop a comprehensive understanding of them. In particular, the scanning electron microscope, which is currently being procured, will be used to record microstructural changes in the model material copper in interrupted tensile and fatigue tests and to make these usable for simulation approaches. The results from tests with a tensile-compression module (ZDM) in the SEM are to be supplemented in this approach, whereby a profound understanding of the material mechanisms taking place is expected. Specifically, after an initial, comprehensive characterisation of the initial condition, copper specimens will be loaded or stressed in tensile and fatigue tests up to damage stages yet to be defined within the scope of the project, and the material response monitored by means of tactile and digital image correlation-based strain, temperature and electrical resistance measurements. The specimens are then transferred to the ZDM, where the processes are monitored using EBSD and high-resolution DIC technology. Afterwards, extensive microstructural characterisations of the damage state in the then existing condition as well as longitudinal and transverse sections take place again. For both initial and final characterisations, laser and digital microscopy, SEM and EDX as well as microhardness, roughness and X-ray diffraction investigations are undertaken. The latter serve to determine lattice strains for the derivation of residual stresses and the integral determination of the dislocation density, which together with the qualitative dislocation distribution determined by means of STEM provides a comprehensive picture of the dislocation processes taking place. By comparing two different specimen preparation methods, the influence of the surface condition caused by the specimen preparation is also considered. All data serve as input variables for the structural-mechanical models.

• DFG Programme: Research Grants