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Abstract

The design of novel high performance steels having superior behavior with respect to high-strength and/or high-temperature durability is closely related to the identification and controlled activation of solid-solid phase transitions. Important examples are e.g. high-manganese TRIP (transformation induced plasticity) and TWIP (twin induced plasticity) steels. To employ and further optimize such steels it is critical to have theoretical modeling tools available that are able to predict the underlying phase transformations and deformation mechanisms on atomic scale as function of the chemical composition with high precision and at realistic conditions (strain, finite temperatures etc.). A powerful tool to do this is the combination of ab initio calculations that are free of any adjustable parameters with thermodynamic concepts to directly compute free energies. A major challenge in realizing this concept is the large number of excitation mechanisms entering the free energy in realistic materials such as harmonic and anharmonic atomic vibrations, magnons, electronic excitation or point defects. In the talk we will give a brief overview how all these contributions can be computed by ab initio techniques, what accuracy can be achieved and what limits remain to be tackled. The power and versatility of this approach will be demonstrated for a few examples covering alloy design, computing phase diagrams or identifying failure mechanisms.