Regensburg 2010 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 43: Materials Design I

MM 43.3: Vortrag

Mittwoch, 24. März 2010, 15:15–15:30, H5

Ab initio study of nano-precipitate nucleation and growth in ferritic steels — •Natalie Tillack, Tilmann Hickel, Dierk Raabe, and Jörg Neugebauer — Max-Planck-Institut für Eisenforschung, Düsseldorf

The hardness of metallic alloys can be substantially improved by inducing the formation of nano-precipitates having dimensions of only a few nm. To realize such structures, chemical compositions and process conditions have to be identified that lead to a spontaneous (self-organized) formation of such structures.

For the example of ferritic alloys we have therefore studied nucleation and growth of such nano-particles combining ab initio calculations and kinetic Monte Carlo simulations. As example we consider the alloy systems Fe-Ni-Mn and Fe-Cu-Si. Using density functional theory and two supercell approaches we determine in a first step formation and interaction energies of Ni, Cu, and Si atoms in an FeMn or an Fe matrix. Our calculations reveal a repulsive interaction for pairs of Ni atoms and Si atoms, whereas the Cu-Cu and the Cu-Si interaction is attractive.

The physical origin for the different behaviour has been investigated, with a particular focus on the charge distribution and relaxation effects in the considered supercells. In a second step the ab initio determined energies are used to construct the Master equation which is solved by a Monte Carlo approach. These simulations provide a very direct insight into the formation and size distribution of the nano-precipitates as function of alloy composition, temperature and the calculated energies.