Prof. Dr. rer. nat. Mayer (Gemeinschaftslabor für Elektronenmikroskopie (GFE), RWTH Aachen University)
The activities in project C1 aim at understanding the relationship between the microstructure, existing interfaces and the formation of defect structures and the properties of the relevant alloy sytems. The investigations aim at revealing the specific relations between the alloy composition and the deformation and hardening mechanisms. In addition we will investigate the atomistic structure of coherent and incoherent interfaces in multiphase alloys and their influence on the dislocation interaction and strain relaxation.
The aim of a predictive materials development in the Fe-Mn-C system can only be reached if the structural and energetic predictions of the ab-initio calculations correctly reflect the behaviour of the phases and defects which determine the properties of the real material. The anticipated theory-driven materials design in our collaborative research centre thus requires a direct experimental verification of the central theoretical predictions down to the atomic level. The modern ultrahighresolution techniques in Transmission Electron Microscopy (TEM) play a key role in this respect. At the same time, various other analytical and diffraction-based TEMprocedures will be applied as fundamental experimental possibilities for linking the macroscopic material properties with the structures and defects (grain and phase boundaries, stacking faults, twins, dislocations) on an atomistic and mesoscopic scale.
A further important goal of C1 is the support of the other experimental sub-projects by supplying the means for a structural and analytical characterization on different length scales and levels of sophistication. Besides high-resolution TEM, other SEMand microanalytical techniques will be applied on a qualitative and quantitative level.
In more detail, the quantitative electron microscope measurements and a comparison of the results with theoretically predicted as well as with experimentally measured properties comprise the following major topics:
• On the structural level: The morphology and chemical composition of the phases and precipitates which are present, as well as the investigation of the existing defect types and defect densities.
• On the atomic level: The structure of the internal boundaries, stacking faults, and twin boundaries, as well as the dislocation cores. Of decisive importance is also the investigation of a possible segregation of impurity atoms to these defects.
• Furthermore, an experimental analysis of the atomistic structure in the bulk and in the area of defects is important for the understanding of the predictions of the ab-initio calculations.
For the investigations with ultra-high resolution electron microscopy and spectroscopy, internationally unique conditions exist at the Ernst-Ruska-Centrum, which was jointly founded by RWTH Aachen University and Research Centre Jülich.
In addition, the existing possibilities for chemical analysis (REM with EDX, microprobe with WDX) and phase- and orientation analysis via electron backscatter diffraction patterns (EBSD) at the GFE will be employed for a detailed analysis of the involved phases and structural defects. In addition, the large chamber scanning electron microscope (LC-SEM), which was financed by the DFG and recently installed at the GFE, can be used for in situ-experiments on the deformation mechanisms.