2, Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf, , Germany
Solid state phase transformations are used for the design of advanced Mn-containing steels and Ti alloys with nano-scale microstructures, where the mechanical properties are controlled by the properties, morphology and interactions of the different microstructural constituents. Specifically the interplay of local defect structures and Gibbs-driven chemical decoration of these defects is an essential vehicle for locally stimulating site specific transformation phenomena.
To this aim we utilize appropriate mechanical and thermal treatments to induce segregation and partitioning phenomena on the nano-scale causing local allotropic and martensitic transformations. By applying multi-scale characterization using scanning electron microscopy, transmission electron microscopy and atomprobe tomography, we study the local elemental partitioning and phase transformations as well as the thermodynamical and structural driving forces causing these local phase transformations at crystal defects and their effect on microstructure and mechanical properties.
We show that through this approach the mechanical properties can be tailored covering a broad range from low yield strength and high ductility to high yield strength and high ductility.