Plenarvorträge - DPG-Tagungen

Metallphysik Montag
M 6 Hauptvortrag Jürgen Horbach
Zeit: Montag 14:00–14:30 Raum: H16
Hauptvortrag M 6.1 Mo 14:00 H16
Computer Simulations of Transport Processes in Multicomponent
Melts — •Jürgen Horbach — Institut für Physik, Johannes
Gutenberg-Universität Mainz, Staudingerweg 7, 55099 Mainz
We use molecular dynamics (MD) computer simulations to investigate
the atomic transport in multicomponent metallic and oxide melts. The
detailed information as obtained by MD allows to elucidate the interplay
between structure, dynamics and phase behavior of liquid mixtures. We
present simulation results for realistic models of ion–conducting alkali silicate
melts and Al–Ni alloys. These systems exhibit intermediate range
M 7 Glasdynamik
order that is reflected by prepeaks in static structure factors. In Al–rich
Al–Ni melts a prepeak is found due to an inhomogeneous distribution of
the Ni atoms and we discuss the importance of this structure for diffusion
dynamics and phase behavior. The intermediate range order in the alkali
silicates provides the presence of diffusion channels for the fast alkali
ion motion. The interplay of the latter channel stucture with non–trivial
transport phenomena such as the mixed alkali effect in ternary alkali silicates
is demonstrated. We show that many aspects of the dynamics in
the considered systems can be understood by the mode coupling theory
of the glass transition.
Zeit: Montag 14:45–16:00 Raum: H16
M 7.1 Mo 14:45 H16
P-32 diffusion in the undercooled melt of Pd43Cu27Ni10P20 —
•Alexander Bartsch 1 , Klaus Rätzke 1 , Volker Zöllmer 1 , Andreas
Meyer 2 , and Franz Faupel 1 — 1 Technische Fakultät, Univ.
Kiel, Kaiserstr.2, 24143 Kiel — 2 TU München, Physik Department E13,
James-Franck-Str., 85747 Garching
Since the development of bulk metallic glasses the undercooled melt is
accessible for diffusion experiments [1]. In an earlier study we have for
the first time determined diffusivity and isotope effect for the Pd-Cu-Ni-P
alloy from the glass to the melt [2]. While in the equilibrium melt diffusivity
and viscosity coincide according to the Stokes Einstein (SE) equation,
they diverge with decreasing temperature down to the glassy state up to
four orders of magnitude. The following questions remain: At which temperature
does the divergence start? Does any constituent determines the
viscosity? In the present study the P-32- and Co-57 tracer diffusion were
studied simultaneously in the range 550 K to 700 K with the radiotracer
technique. The present, preliminary data show: the Co-diffusivities are
in the expected range. The P-32 diffusivities are a factor of two smaller.
Hence, Phosphorus does not determine the viscosity despite its covalent
bonding character.
[1] F. Faupel, W. Frank, M.-P. Macht, H. Mehrer, V. Naundorf, K.
Rätzke, H. R. Schober, S. K. Sharma, H. Teichler, Review of Modern
Physics 75 (2003) 237 [2] V. Zöllmer, K. Rätzke, F. Faupel, A. Meyer,
Phys. Rev. Lett., 90, 195502-1 (2003).
M 7.2 Mo 15:00 H16
On the relation between fragility, thermodynamic properties
and thermal stability of Pd-rich bulk-glass forming alloys —
•Gerhard Wilde — Forschungszentrum Karlsruhe, Institute of Nanotechnology,
P.O.B. 3640, 76021 Karlsruhe
It has been suggested that thermal stability and fragility of (metallic)
glasses are related such that the less fragile systems are more stable.
Moreover, it has been proposed that fragility and the temperature dependence
of the excess thermodynamic properties, e.g. the differences
in specific heat between the undercooled melt and the crystalline equilibrium
phases are directly correlated. Consequently, it would be expected
that the most fragile systems show the highest stability and the
largest temperature dependence of the excess thermodynamic properties,
especially if chemically similar alloys are compared. In order to check
these assumptions, a complete set of experimental data for different Pdrich
bulk glass forming alloys, i.e. Pd40Ni40P20, Pd77.5Cu6Si16.5 and
Pd43Cu27Ni10P20, has been used to perform a detailed comparison between
the fragility characteristics and the thermal stability of the chemically
similar alloys.
M 7.3 Mo 15:15 H16
Mechanical spectroscopy of the bulk metallic glasses
Zr52.5Ti5Cu17.9Ni14.6Al10 and Pd40Cu30Ni10P20.
— •Maik Eggers 1 , Alexander Strahl 1 , V.A. Khonik 2 , and
Hartmut Neuhäuser 1 — 1 TU Braunschweig, Institut für Metallphysik
u. Nukleare Festkörperphysik, Mendelssohnstr. 3, D-38106
Braunschweig — 2 Institute of General Physics, State Pedagogical
University, Voronezh, Russia
By means of the vibrating reed technique, measurements of internal
friction have been performed in the temperature range of 120 to 800K
during heating and cooling with a constant rate of 2K/s, in order to
monitor the structural relaxation during these thermal treatments. This
is compared for bulk glasses (produced with rather low quenching rate)
and for the same materials in form of ribbons quenched rapidly from the
melt. Special investigation is devoted to a low temperature relaxation
peak around 270K (for first flexural vibration mode between 100 and
400Hz) which has been found in the Zr-based alloy, and which may arise
either from trapped hydrogen or from ”dislocations” introduced by plastic
deformation into the amorphous structure. Therefore in particular the
amplitude dependence of damping has been measured.
M 7.4 Mo 15:30 H16
Mechanische Spektroskopie am amorphen ZrAlCu-System -
Hinweise auf einen ” excess wing“ in metallischen Gläsern —
•Peter Rösner, Susanne Schneider und Konrad Samwer — I.
Physikalisches Institut, Georg-August-Universität Göttingen, Tammann-
Str. 1, 37077 Göttingen
Mit dem Doppel-Paddel-Oszillator (DPO) als Substrat wurden mechanische
Eigenschaften von aus der Gasphase kokondensierten, dünnen
Schichten des amorphen, metallischen Glases ZrAlCu untersucht. Dazu
wurde der DPO bei einer Frequenz von 5400 Hz in seiner antisymmetrischen
Torsionsmode angeregt und temperaturabhängig der Einfluss der
Schicht auf die Eigenfrequenz und und die Dämpfung gemessen.
Aus den Daten lässt sich die innere Reibung und der komplexe Schermodul
der Schichten bestimmen. Der Verlustmodul kann bei Temperaturen
oberhalb des Glasübergangs durch eine Havriliak-Negami-Funktion
mit einer Vogel-Fulcher-Tammann abhängigen Relaxationszeit beschrieben
werden. In der Nähe des Glasübergangs in Richtung tiefere Temperaturen
zeigt sich ein klares Abweichen der Messwerte von dieser Funktion.
Dies könnte auf die Existenz eines ” excess wing“ auch in metallischen
Gläsern hinweisen, was die These stützen würde, dass es sich hierbei um
eine universelle Glaseigenschaft handelt. Jedenfalls sind die Messdaten
sehr ähnlich solchen, die durch dielektrische Spektroskopie in vielen anderen
amorphen Materialien beobachtet wurden.
Die Arbeit wird von der DFG im Rahmen des GRK 782 und des SFB
602 Projekt B8 gefördert. Der Dank der Autoren gilt insbesondere P.
Lunkenheimer und A. Loidl für viele hilfreiche Diskussionsbeiträge.
M 7.5 Mo 15:45 H16
Mechanisms of ion irradiation-induced viscous flow in glasses:
the role of point defects — •S.G. Mayr — I. Physikalisches Institut,
Georg-August-Universität Göttingen, Tammannstr. 1, 37077 Göttingen
The nature of ion irradiation-induced viscous flow in amorphous solids
is inverstigated using experiments and molecular dynamics computer simulations.
Experimentally, relaxation of film stresses and smoothing of
rough surfaces illustrate, that many amorphous solids undergo Newtonian
flow far below their respective glass temperature during ion bombardement
[1]. Using molecular dynamics computer simulations we study the
atomic-scale mechanisms governing radiation-induced viscous flow under
conditions, where local melting along the ion tracks is not dominant. We
show, that injection of interstitial- and vacancy-like defects induces the
same amount of flow as recoil events, indicating, that point-defect-like
entities in the amorphous matrix act as local shear instabilities and mediate
viscous flow [2].
Financially supported by the DFG - SFB 602, TP B3