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PV: Plenarvorträge

PV XII

PV XII: Plenarvortrag

Mittwoch, 2. April 2014, 14:00–14:45, HSZ 02

Materials physics on its way to in-depth understanding of real materials — •Reiner Kirchheim — Georg-August-Universität Göttingen, Göttingen, Germany

Man-made materials used in real life are single crystalline, polycrystalline or amorphous with properties optimized by controlling the defect structure and composition of the material. Any further development to novel and advanced materials requires an in-depth understanding of the generation of defect-structures and their interaction with the various chemical components. For instance making materials harder defect generation has to be suppressed and/or their motion has to be retarded. The latter is often achieved effectively by adding solute atoms which interact attractively with the defect where solute occupancy is described by Fermi-Dirac-Statistics. Then the defects have to drag along a solute cloud reducing its velocity. If defects are defined more generally as discontinuities of atom coordination, one can easily show that their formation energies are decreased by segregating atoms or molecules. This comprises the well-known reduction of the surface energy by surfactants. In analogy atoms reducing formation energies of vacancies, dislocations and interfaces etc. are called defactants. Depending on whether the rate determining process is defect motion or generation materials are softened or hardened. The relevance of the defactant concept is exemplified for high strength steels with carbon as a defactant in iron, hydrogen embrittlement or new design rules for nanocrystalline alloys.