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For materials comprised of a heterogeneous microstructure the mechanical properties of individual phases and their synergetic behavior during the deformation process are currently still not fully understood, especially for steels containing hard and brittle non-metallic inclusions. Their active slip systems and corresponding critical resolved shear stress, the fracture toughness of phases and boundaries, the tolerable plastic deformation at interfaces remain unknown. Therefore, the goal of project B03 is to measure the abovementioned material properties quantitatively, which are inaccessible in macroscopic experiments. Besides, attention will also be paid to the dislocation interaction behavior at interfaces.

Methodologically, the mechanical properties of individual phases are investigated through the micropillar compression and microcantilever bending test, where the possible specimen size ranges from 100 nm to 15 µm. Moreover, the complex interaction of phases at their interfaces is supposed to be measured by pillar compression tests containing a bicrystal. All samples will be prepared by FIB milling and the microstructure evolution investigated by the SEM, TEM, or µLaue method. In this way, a mechanism-based material model is possible.

In order to avoid the blind test and reduce the tested specimen numbers, only the sensitive regions where cracks initiate are investigated. Project B02 is supposed to provide the information of these specific sites. In return, project B03 tries to offer characteristic material parameters, such as the orientation- and size-dependent strength of individual phases as well as their critical resolved shear stress, to our simulation partners as the real input parameters. Apart from this, the mechanism-based local failure model is capable of giving a criterion for designing materials requiring damage-tolerant interfaces.

Project leader
Prof. Dr. mont. Christoph Kirchlechner
Karlsruhe Institute of Technology (KIT)
Institute of Applied Mechanics - Materials and Biomechanics

Dr.-Ing. Dirk Ponge
Max-Planck-Institut für Eisenforschung GmbH (MPIE), Düsseldorf
Department of Micro Structure Physics and Alloy Design

Project coordinator
Angelica Medina Gomez, M. Sc.
Institute for Applied Materials - Mechanics of Materials and Interfaces (IAM-MMI), KIT