Project area C comprises local structure-, defect-, and chemical analysis,
characterization of technologically relevant mechanical properties, evaluation of the local texture and anisotropy, description of the failure mechanisms under mechanical load, as well as a detailed analysis of the relationship between lattice defects and internal strain in the system Fe-Mn-C.
The main focus of sub-project C1 is the characterization of the atomistic structures of the phases involved, internal boundaries and interfaces, as well as stacking faults and twin boundaries with the help of high resolution SEM and TEM imaging techniques. Furthermore, high resolution analytical techniques are used for the characterization of local chemical compositions and fluctuations. Quantitative microprobe analysis will reveal information on microsegregations, which is of particular interest e.g. in sub-project A4. Furthermore, for the comparison with the predictions of the ab initio calculations, an experimental analysis of the electronic structure in the bulk and in the area of defects in the occurring phases will be performed with electron spectroscopic techniques. The microstructural results will also help to improve the mechanism chart in sub-project A5.
Sub-project C2 combines the development of a novel analysis technique, with which the TWIP-effect can be visualized in situ, with an extensive characterization of the macroscopic mechanical properties. The mechanical properties are determined in a temperature range from -40°C to 180°C, which is relevant for the intended industrial applications. In addition, creep curves are recorded for the validation of the micromechanical models developed in A7.
The local mechanical properties of the investigated materials are determined via nanoindentation in sub-project C3. For this purpose, chemically pure thin films are deposited, whose local mechanical properties are also of interest in sub-project A2. In addition the local mechanical properties of the technical alloys produced in B1 are determined.
In further investigations, the basic mechanisms of texture development in multiphase steels will be determined and analysed in sub-project C4. For this purpose, information on the free enthalpies as well as the mesoscopic topology of the different phases after primary solidification is gathered (among others based on results of A2, A3, A6, and C1). The resulting information will be used for micromechanical modelling on the basis of crystal-plasticity-FEM methods in sub-project A7. The corresponding experiments will be carried out on the basis of the newly developed technique of simultaneous 3D-orientation and phase determination on a FIB-SEMEBSD instrument, which was introduced by the MPIE.
Sub-project C5 is concerned with the determination of the internal strains occurring on the micro and macro level. These results are particularly important for sub-project C6, which deals with the failure mechanisms and the optimization of the limits of plastic forming of the developed steels. There exists a close co-operation between the latter two sub-projects. The results of both projects can further be utilized in subprojects B2 and B3 for optimising the deformation parameters, as well as for the validation of the models developed in A7. As special feature, it should be mentioned that in sub-project C5 the internal strain will be determined via (Synchroton-) X-ray and neutron diffraction near the surface as well as in the bulk of the sample.