Plenarvorträge - DPG-Tagungen

Metallphysik Donnerstag
M 32 Grenzflächen und Wachstum
Zeit: Donnerstag 16:30–17:30 Raum: H4
M 32.1 Do 16:30 H4
Interface Structure and Segregation Effects of Nanocrystalline
PdZr in Dependence of Temperature — •H. Weigand 1 , W.
Sprengel 1 , T. Wejrzanowski 2 , C. E. Krill 3 , R. Röwer 1 , M.
Kelsch 4 , and H.-E. Schaefer 1 — 1 Inst. f. Theor. u. Angew. Phys.,
Univ. Stuttgart, D-70569 Stuttgart — 2 Faculty of Mat. Science. a. Engin.,
Warsaw Univ. of Techn., 02-507 Warszawa, Poland — 3 Techn. Phys.,
Univ. d. Saarlandes, D-66041 Saarbrücken — 4 MPI f. Metallf., D-70569
Stuttgart
Grain growth of n-PdZr alloys is expected to be reduced by segregation
of Zr in the grain boundaries. Positron annihilation spectroscopy
was employed to study this effect and the temperature dependence of
the interface structure, showing a decrease of the fraction of nanovoids,
the size of 10 to 15 missing atoms, upon isochronal annealing up to 1100
K.
Temperature dependent studies after annealing at 1100 K show a reversible
increase of the mean positron lifetime with temperature due to
a reversible change of the positron trapping behavior at interfacial free
volumes. The variation of the interfacial composition with temperature
is investigated.
M 32.2 Do 16:45 H4
Monte Carlo Simulation and Statistical Theory of Normal Grain
Growth in Two and Three Dimensions — •Dana Zoellner and
Peter Streitenberger — Otto-von-Guericke-Universitaet Magdeburg,
Institut fuer Experimentelle Physik, Abteilung Materialphysik, PF
4120, D-39016 Magdeburg
A modified Monte Carlo algorithm for single-phase normal grain
growth is presented, which allows one to simulate the time development
of the microstructure of very large grain ensembles in two and three dimensions.
The emphasis of the present work lies on the investigation
of the interrelation between the local geometric properties of the grain
network and the grain size distribution function in the quasi-stationary
self-similar growth regime. It is found that the topological size correlations
between neighbouring grains and the resulting average statistical
growth law, both in two and three dimensions, deviate strongly from the
assumptions underlying the classical Lifshitz-Sloyzov-Hillert theory. The
average local geometric properties of the simulated grain structures are
used in a statistical mean-field theory to calculate the grain size distribution
functions analytically. By comparison of the theoretical results
with the simulated grain size distributions it is shown how far normal
grain growth in two and three dimensions can successfully be described
by a mean-field theory and to what extent stochastic fluctuations in the
average growth law must be taken into account.
M 32.3 Do 17:00 H4
Grain Growth under the Influence of Mechanical Stress Fields
— •Myrjam Winning — Institut für Metallkunde und Metallphysik,
RWTH Aachen
The motion of grain boundaries is the key phenomenon of recrystallization
and grain growth and dominates the evolution of texture and
microstructure, i.e the macroscopic physical and mechanical properties
of a material, in particular of a part in service. The reaction of grain boundaries
to mechanical stresses is reviewed. It was found that the motion
of low angle grain boundaries as well as of high angle grain boundaries
can be induced by the imposed external stress. The observed activation
enthalpies allow conclusions on the migration mechanism of the stress induced
grain boundary motion. From these experiments can be seen that
mechanical stress fields can change the dynamical behaviour of grain
boundaries. Therefore in the following the influence of mechanical stresses
on grain growth was studied. The experiments should investigate the
change of the grain growth kinetics as well as the microstructure and
texture evolution in polycrystalline high-purity aluminium under the influence
of different mechanical stress fields. The fact that boundaries can
also be moved by mechanical forces sheds new light on microstructure
evolution during elevated temperature deformation.
M 32.4 Do 17:15 H4
Crossover-Vergröberungsverhalten von AlSn-Legierungen —
•M. Ziehmer 1 , C. E. Krill III 1 , L. Helfen 2 und R. Birringer 1
— 1 FR 7.3 Technische Physik, Universität des Saarlandes, Geb. 43B,
D-66123 Saarbrücken — 2 ESRF, BP 220, F-38043 Grenoble Cedex
Konventionelle AlSn-Legierungen stellen Modellsysteme zum Studium
der Ostwald-Reifung von Al-Kristalliten in einer flüssigen Sn-Matrix dar.
Im Grenzfall hoher Volumenanteile der festen Phase (> 90%) ist a priori
unklar, ob die bekannte Ostwald-Reifungskinetik noch gültig ist. Wir berichten
über erste experimentelle Ergebnisse an solchen Legierungen, die
eine ” Crossover-Kinetik“ zwischen konventioneller Ostwald-Reifung und
normalem Kornwachstum belegen. Diese Befunde implizieren, daß bei
einer weiteren Vergrößerung des festen Phasenanteils, aber endlicher Sn-
Konzentration, eine Vergröberungskinetik nach den Gesetzmäßigkeiten
des normalen Kornwachstums zu erwarten ist. Solche Systeme sind
prädestiniert für Untersuchungen des Echtzeit-Kornwachstums mittels
Röntgentomographie.