The stress and functional behaviour of a component is significantly influenced by its chemical, physical and mechanical properties.
Knowledge of these properties is therefore a decisive prerequisite for understanding and optimizing heat-treated, machined or coated components made of high-strength structural materials. Consequently, the application and further development of physical investigation methods for the characterization of microstructure and residual stress states are the main focus of research within the department.
The measuring methods include in particular optical emission spectroscopy, radiographic fine structure measuring methods and micromagnetic methods. The possibilities of the large-scale research facilities (neutron and synchrotron radiation) are also used in the research activities of the department. The further development and application of in-situ X-ray diffraction methods are an important focus of the research activities of the Department of Physical Analysis.
Physical analytics is strongly experimentally oriented
The department of physical analysis is strongly experimentally oriented and has 20 modern X-ray diffractometers for fine structure analysis which are optimized for different applications. These allow, among other things, investigations with high spatial resolution by micro-beam optics, analyses of thin films under grazing incidence, measurements of large components and in production facilities by two mobile diffractometers as well as investigations with high time resolution for in-situ experiments. In addition, different methods with neutron and synchrotron radiation are applied and further developed in the research projects of the department.
The resulting material states, in particular the residual stresses, are analysed according to different manufacturing processes within the scope of various projects, partly with external cooperation partners, using the existing measuring methods. Within the priority program SPP2013, the mechanisms of residual stress generation during rotary swaging are currently being investigated in order to optimize the component properties in a targeted manner.
In-situ X-ray diffraction methods in the laboratory and at large-scale research facilities
The research and application of in-situ X-ray diffraction methods in the laboratory and at large-scale research facilities is a major focus of the research activities of the Department of Physical Analysis. Currently, various processes using laboratory X-ray sources are being fundamentally investigated, such as tempering effects in different steels or the formation of compound layers during nitriding. Thereby, fundamental aspects of material-physical mechanisms are investigated as well as new measuring methods for future sensors for process monitoring in industrial processes are developed.
In addition to the laboratory procedures, various experiments are carried out at synchrotron facilities. At the European Synchrotron Radiation Facility (ESRF), for example, the development of hydrostatic stresses in (residual) austenite during martensitic transformation during quenching could be followed over time and experimentally verified for the first time. The application of synchrotron radiation for in-process investigation of microstructure and stress development has been extended to other processes in recent years. Within the SFB TRR 136 "Process Signatures" a deep rolling process was simulated and analysed by different experimental approaches at the synchrotron (ESRF) and with neutron radiation at the Institut Laue-Langevin (ILL). The determined 2-dimensional stress and strain distributions could be used to develop process signatures for a process-independent prediction of the residual stress distributions during deep rolling.
Micromagnetic processes form a further research focus
Current research activities on the application of synchrotron radiation for in-process investigations are currently underway in the fields of additive manufacturing using laser powder cladding or in thermo-mechanical processes such as the continuous bainitization of forged steels within the framework of the DFG's Bragecrim Program at the German Electron Synchrotron in Hamburg (DESY). In addition, low-pressure carburizing is currently being investigated in-situ using a self-developed experimental setup with synchrotron radiation. The local microstructure and stress development is analyzed with spatial and time resolution.
Micro-magnetic processes form a further research focus with basic and application-oriented questions in order to enable reliable non-destructive analyses of material properties and boundary layer states. New approaches for depth-dependent measurement of residual stresses and hardness based on frequency-dependent signal acquisition and evaluation have already been investigated. The capabilities of a Barkhausen eddy current microscope for the fast acquisition of material and component properties on the microscale are currently being tested and further developed within the framework of SFB 1232 "Coloured states". Finally, new approaches for non-destructive testing of grinding burns in industrial production are being developed and directly implemented in practice within the framework of bilateral research projects with industry.
In addition, new strategies will be developed within the priority program SPP2086 to enable the application of this measurement technique in grinding plants.