Ab initio thermodynamics: A novel route to understand and design structural materials

Jörg Neugebauer

Fritz Körmann, Ali Nematollahi, Blazej Grabowski, and Tilmann Hickel

Max-Planck-Institut für Eisenforschung, Max-Planck-Str. 1, 40237 Düsseldorf, Germany

A key requirement in developing computational tools to design structural materials with superior mechanical properties is the availability of accurate yet efficient methods that allow determining formation or migration energies not only at T = 0 K but also under realistic conditions, i.e., at finite temperature. Combining accurate first principles calculations with mesoscopic/macroscopic thermodynamic and/or kinetic concepts allows now to address this issue and to determine free energies and derived thermodynamic quantities such as heat capacity, thermal expansion coefficients, and elastic constants with an accuracy that often rivals available experimental data. The flexibility and the predictive power of these approaches to determine/predict defect and microstructure properties and the impact they can have in developing new strategies in achieving tailored microstructures will be discussed for a few examples: One example will address modern high-manganese steels that due to a carefully designed chemical composition achieve an adaptive microstructure that combines high strength with excellent formability (ductility). Further examples will focus on ultra-high strength pearlitic steels and understanding the mechanisms behind H embrittlement in high-strength steels.