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  5. Physical Analysis
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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, X-ray fine structure measurement 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.

 

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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.

Projects of the Physical Analysis

Non-destructive characterization of grinding-generated surface-layer modifications depending on the material condition using micromagnetic testing methods (FVA 723 III)

Aim of this project is the investigation of so far unknown effects on the micromagnetic detection of thermo-mechanical surface damages at ground gear flanks. Based on previous projects, investigations are carried out on profile and generating ground gears from case-hardening steel 20MnCr5 in different heat treatment conditions.

 

 

Cooperation: Leibniz-IWT WT/FT
Funding: BMWi-AiF/IGF (FVA)

 

Contact:
Dr.-Ing. Jérémy Epp
Tel.: +49 421 218 51335 
E-Mail: epp@iwt-bremen.de

Improving the fatigue strength of rivet lap joint of aerospace grade 7xxx series aluminum by laser shock peening

Cold expansion is a widely adopted technique to enhance the fatigue life of riveted lap joints.

However, it presents several drawbacks such as the presence of a compression-to-tension transition, which may act as a site for crack initiation. This project, therefore, aims to investigate the potential of laser shock peening for riveted lap joints.

 

 

Cooperation: Airbus SE
Funding: BMWK/(Luftfahrtforschungsprogramms VI-2)

 

Contact:
Dr.-Ing. Jérémy Epp
Tel.: +49 421 218 51335 
E-Mail: epp@iwt-bremen.de

Mechanism-based analysis and optimization of additive manufacturing process for hardenable tool steel by means of In situ X-ray diffraction experiments

The application of Laser-directed energy deposition (L-DED) for hardenable steel involves many thermal cycles leading to complex microstructure evolution that critically affects the component mechanical properties.

This project aims to evaluate in details the microstructure evolution during the LMD process of steel X40CrMoV5-1 by in situ X-ray diffraction in combination with Atom probe tomography (APT) and understand how these complex thermal cycles affect the microstructure of L-DED components.

 

Funding: DAAD (PKZ91793403)

 

Contact:
Dr.-Ing. Jérémy Epp
Tel.: +49 421 218 51335 
E-Mail: epp@iwt-bremen.de 

Targeted surface layer properties by inprocess- monitoring and adaptive process control during grinding

In this project, the potential of a grinding process control based on a soft sensor was shown. The soft sensor combines a thermal limit depending on specific grinding power and contact time with the Barkhausen noise measured in-process.

The soft sensor combines a thermal limit that depends on the contact surface-related grinding power Pc'' and contact time Δt, which makes it possible to exclude tempering zones, with the Barkhausen-noise measured in-process. When using CBN as a cutting material, a shift in the process limit determined for corundum was observed. In addition to the generated edge zone condition, the Barkhausen-noise is also influenced by the mechanical effect of the grinding wheel engagement, which 
primarily affects the signal in the saturation range.

 

Cooperation: Leibniz-IWT WT/FT, Fraunhofer IWU Chemnitz 
Funding: DFG (SPP 2086)

 

Contact:
Dr.-Ing. Jérémy Epp
Tel.: +49 421 218 51335 
E-Mail: epp@iwt-bremen.de 

Improved process understanding for case hardening with carburizing at low pressure based on in situ X-ray diffraction experiments

In the second phase of the project, the primary objective was to improve the developed experimental low-pressure carburizing (LPC) system and expand the understanding of the LPC process to different steel grades and include the tempering step in the experimental approach.

For this purpose, a completely new process chamber with active compensation of the sample position by means of laser triangulation was designed. Two measurement campaigns with in-situ experiments were successfully carried out on beamlines P21 and P07 at DESY in Hamburg. Various process parameters were investigated and, among other things, the influence of the boost duration on the formation and re-dissolution of carbides was analyzed. In addition, combined SAXS/WAXS measurements were carried out during annealing to track the formation of fine carbides with temperature and time resolution. 

 

Cooperation: KIT(-IAM-WK) 
Funding: DFG, EP-128/2-2

 

Contact:
Dr.-Ing. Jérémy Epp
Tel.: +49 421 218 51335 
E-Mail: epp@iwt-bremen.de  

Transregional CRC 136 “Process Signatures” – Transfer project T08: Material load oriented development of diamond tools for energy assisted cutting processes

In the transfer-project T08 of the CRC 136, the dependence of local material loads based on the tool geometry in energy-assisted diamond machining of silicon is determined.

With the material load-oriented approach of process signatures, here applied to silicon for the first time, the influence of a targeted variation of mechanical and thermo-mechanical material loads on geometrically determined machining is examined.

 

Cooperation: Gruppe Matzdorf GmbH 
Funding: DFG (SFB/TRR 136)

 

Contact:
Dr.-Ing. Jérémy Epp
Tel.: +49 421 218 51335 
E-Mail: epp@iwt-bremen.de  

Partitioning-driven heat treatments for the microstructural tailoring of additively manufactured medium manganese steels

Medium manganese steels are increasingly used due to their excelling mechanical properties. Nevertheless, their high Mn content makes their production challenging.

This project aims to tackle this downside by replacing conventional casting with additive manufacturing. Furthermore, the chemical heterogeneities left by the manufacturing step offer possibilities for shortening heat treatment times and tailoring the microstructure in order to achieve various mechanical properties.

 

Funding: DFG

 

Contact:
Dr.-Ing. Jérémy Epp
Tel.: +49 421 218 51335 
E-Mail: epp@iwt-bremen.de 

Targeted surface layer properties by in-process-monitoring and adaptive process control during grinding

In this project, the potential of a grinding process control based on a soft sensor was shown. The soft sensor combines a thermal limit depending on specific grinding power and contact time with the in-process measured Barkhausen noise.

Cooperation: Leibniz-IWT WT/FT, Fraunhofer IWU Chemnitz
Funding: DFG (SPP 2086)

Contact:
Dr.-Ing. Jérémy Epp 
Tel.: +49 421 218 51335 
E-Mail: epp@iwt-bremen.de