Plenarvorträge - DPG-Tagungen

Metallphysik Dienstag
M 18 Postersitzung
Zeit: Dienstag 14:30–16:30 Raum: Saal C
M 18.1 Di 14:30 Saal C
Molecular dynamics study of local atomic structures in liquid
metals — •Magnus Kreth and Peter Entel — Institut für Physik,
Universität Duisburg-Essen, 47048 Duisburg
In this work we study local atomic structures in liquid aluminum and
iron using molecular dynamics simulations. Interatomic interactions are
modelled using an embedded-atom method potential. Local atomic structures
in the liquid are identified using a common-neighbor analysis. Static
structure factors are calculated from the pair distribution function to
compare our results with recent neutron diffraction experiments on liquid
metals.
M 18.2 Di 14:30 Saal C
Elektronenmikroskopische Untersuchungen an Nd60Fe30Al10-
Legierungen — •T. Niermann 1 , A. Bracchi 2 , M. Seibt 1 ,
K. Samwer 2 und S. Schneider 1 — 1 IV. Physikalisches Institut
der Universität Göttingen, Tammannstr. 1, 37077 Göttingen — 2 I.
Physikalisches Institut der Universität Göttingen, Tammannstr. 1,
37077 Göttingen
Die Mikrostruktur von Nd60Fe30Al10-Proben wurde mittels hochauflösender
Transmissionselektronenmikroskopie (HRTEM) und
energiedispersiver Röntgenanalyse (EDX) untersucht, sowie die magnetischen
Eigenschaften der Proben mit einem SQUID-Magnometer bei
unterschiedlichen Temperaturen gemessen. Die untersuchten Proben
wurden bei verschiedenen Abkühlraten hergestellt: dünne Schichten,
schnell abgeschreckte Folien (Splat-Quenching) und massive Proben.
Die TEM-Aufnahmen zeigen nanokristalline Nd-Ausscheidungen eingebettet
in einer amorphen Matrix. Im Amorphen lassen sich außerdem
zwei verschiedene Nahordnungen finden. Die bei der vorgefundenen Mikrostruktur
zu erwartenden domain-wall-pinning Prozesse und die magnetische
Kopplung zweier amorpher Phasen können das magnetische
Verhalten erklären.
Gefördert durch die DFG im Rahmen des SFB 602.
M 18.3 Di 14:30 Saal C
Tomographic atom probe (TAP) study of the chemical ordering
in Zr60Ni25Al15 bulk amorphous alloy — •Ahmed Shariq,
Talaat Al-Kassab, and Reiner Kirchheim — Institut fuer Materialphysik,
Uni- Goettingen, Tammanstr.1,D- 37077, Goettingen, Germany
Bulk amorphous alloys are advanced engineering materials owing to
their excellent static and dynamic mechanical properties, wear properties,
low coefficient of friction, magnetic properties and corrosion properties.
The new amorphous alloys have much wider supercooled liquid region
defined as the difference between crystallisation and glass transition temperatures
which may extend up to 100K for some alloys. This wider range
allows to explore the kinetics and thermodynamics in this region. The
alloys with stabilized supercooled liquid state have three features in their
alloy components i.e., multicomponent system, significant atomic size ratios
above 12 percent and negative heat of mixing. Molecular-Dynamics
(MD) simulations for a model Zr60Ni25Al15 ternary amorphous alloy
already had shown two types of chemical short range ordering of Al and
Ni sub systems. The 3D-tomographic atom probe (TAP) is proved to be
currently the best experimental tool to gain experimental information
on chemical heterogeneities at the atomic scale. The data from TAP has
been used to elucidate the atomic distances among neighbouring atoms.
The chemical short range ordering in the supercooled liquid region will
be discussed on the basis of TAP results.
M 18.4 Di 14:30 Saal C
Dichte und Oberflächenspannung flüssiger Fe-Ni-Cu Legierungen
— •Jürgen Brillo und Ivan Egry — Deutsches Zentrum für
Luft- und Raumfahrt e.V., Institut für Raumsimulation, 51147 Köln
Es werden Messungen der Dichte und Oberflächenspannung an den
flüssigen Legierungssystemen Nickel-Eisen, Kupfer-Nickel und Kupfer-
Eisen vorgestellt. Die Messungen werden mit Hilfe der elektromagnetischen
Levitation sowohl bei Temperaturen oberhalb wie unterhalb des
Schmelzpunktes durchgeführt. Die Oberflächenspannung wird mit der
Methode des schwingenden Tropfens aus den Frequenzen der Oberflächenschwingungen
bestimmt. Die Dichte folgt aus einer Volumenbestimmung
des levitierten Tropfens. Die Messergebnisse werden anhand
von Modellen diskutiert. Es zeigen sich charakteristische Unterschiede
zwischen den drei binären Legierungssystemen.
M 18.5 Di 14:30 Saal C
Phase-field Simulations of Dendritic Patterns in Solidification
of a Pure Substance — •Denis Danilov 1 , Britta Nestler 1 , and
Peter Galenko 2 — 1 University of Applied Sciences Karlsruhe, Germany
— 2 Institute for Space Simulation, DLR, Cologne, Germany
We present a critical analysis of the existing phase-field models of
solidification patterns in pure substances. For comparison of the predictions
and asymptotic solutions, we apply the phase-field model recently
developed by Garcke, Nestler, Stinner [2] including the ”thininterface”analytical
results by Karma et al. [1]. The model equations
describing are numerically solved using two different methods: A finitedifference
discretization and an adaptive finite-element method. Simulation
results of solidifying 2D and 3D dendritic morphologies are presented.
The numerical methods are examined with respect to the influence
of grid anisotropy and computational efficiency. The phase-field
model predictions of the tip radius and velocity for different undercoolings
are compared with the analytical model of Brener [3] and with new
experimental results of solidified nickel dendrites by Funke et al. [4].
[1] A. Karma and W.-J. Rappel, Physical Review E 53 (1996) R3017 and
Physical Review E 60 (1999) 3614
[2] H. Garcke, B. Nestler und B. Stinner, SIAM J. on Appl. Math., in
print
[3] E. Brener, J. Cryst. Growth 99 (1990) 165
[4] O. Funke, G. Phanikumar, P.K. Galenko, M. Kolbe, D.M. Herlach,
Physical Review E (2004) submitted
M 18.6 Di 14:30 Saal C
Phase-field modeling of stress-induced instabilities during directional
solidification of a binary alloy — •Bo Liu and Klaus Kassner
— Institut für Theoretische Physik, Otto-von Guericke-Universität
Magdeburg
A phase-field approach is developed to investigate the effect of elastic
stresses on the morphological instability during directional solidification
of a binary alloy. Governing equations are developed to simulate
microstructural pattern formation based on a combination of the quantitative
model for alloy solidification by Karma (Phys. Rev. Lett. 87,
115701 (2001)) and the model for the Grinfeld instability by Kassner et
al. (Phys. Rev. E 63, 036117 (2001)). Simulations in two dimensions are
carried out to test the accuracy of the present model and its numerical
utility by reproducing some known results. We then proceed to investigate
the combined effects of thermal and compositional strains as well as
experimental control parameters on the morphological instability.
M 18.7 Di 14:30 Saal C
A relativistic description for the positron annihilation in solids
— •Diana Benea 1 , Zsuzsanna Major 2 , and Hubert Ebert 1 —
1 Department Chemie / Physikalische Chemie, Universität München, Butenandstr.
5-13, D-81377 München, Germany — 2 H. H. Wills Physics
Laboratory, University of Bristol, Tyndall Avenue, BS8 1TL Bristol, UK
A fully relativistic formulation for the of spin resolved momentum
density is presented together with a corresponding scheme to determine
the two dimensional projection of the electron-positron momentum
density for metals. This formalism is set up within the framework of
spin-polarised relativistic Korringa-Kohn-Rostoker (SPR-KKR) method
of bandstructure calculations. The resulting two dimensional projection
of the electron-positron momentum density is usually identified with the
two-dimensional angular correlation of the annihilation radiation (2D-
ACAR) experimental spectra. Various two dimensional projections of
the electron-positron momentum density of vanadium are presented and
compared with nonrelativistic LMTO calculation and experimental data.
M 18.8 Di 14:30 Saal C
Phase formation by interfacial reactions in the BaO - TiO2 system
— •Andreas Graff, Stephan Senz, and Dietrich Hesse —
Max-Planck-Institut für Mikrostrukturphysik, Halle, Germany
Model experiments concerning phase formation during BaTiO3 genesis
by interfacial reactions in ceramics were performed to identify the
reaction mechanism. Reaction products between BaO vapour and ru-