Public Physic Colloquium in the Summer Terms 2012 in Münster
Place:     Germany, 48149 Münster, Wilhelm-Klemm-Str. 10, IG I, HS 2
Time:     Thursday, 12.04.2012  16:00 h c.t.
Colloquium Coffee at 15:45 h  at the Lecture Hall

Physics at grain boundaries: a combined study of diffusion, segregation and phase transformations
Dr. Sergii Divinskyi, WWU Münster, Institut für Materialphysik

Inherent defects in the crystalline state of materials determine a broad spectrum of important properties and hence come into our everyday life. The 0-D defects (e.g. vacancies or interstitial atoms) govern atomic transport in materials, while the 1-D and 2-D defects (dislocations and interfaces, respectively) provide often the short-circuit paths for an enhanced atomic transport. Segregation of alloy elements or residual impurities to these crystalline defects crucially affects the material properties and could be both beneficial (e.g., the activated sintering) or detrimental (e.g., low-temperature stress-assisted corrosion or segregation-induced embrittlement), just to call a few crucial phenomena.
In this talk the recent advances in the experimental investigation of kinetic and thermodynamic properties of internal interfaces (grain boundaries) in polycrystalline materials will be presented. It will be demonstrated that the diffusion properties of even single interfaces can reliably be measured now that allows a consistent assessment of the fundamental structure–property relationships.
Solute segregation at grain boundaries may invoke new effects and even provoke specific grain boundary phase transitions. The grain boundary wetting (melting) transitions in the Cu–Bi and Al–Ga systems will be considered. For example, a dramatic increase of the grain boundary diffusion rate is observed in the two- phase (solid+liquid) region of the Cu–Bi phase diagram. Such a grain boundary diffusion enhancement exists even in the single phase (solid solution in Cu) region manifesting the existence of a pre-wetting interface-related phase transition in this system.

Invited from: Prof. Dr. G. Wilde

By Order of the Professors of the Department of Physics

Prof. Dr. Sergej Demokritov