Plenarvorträge - DPG-Tagungen

Metallphysik Montag
M 9.2 Mo 16:45 H16
Microstructure, thermal stability and mechanical properties
of slowly cooled Zr-based composites containing dendritic bcc
phase precipitates — •Nicolle Radtke 1 , Juergen Eckert 2 , Uta
Kuehn 1 , Mihai Stoica 1 , and Ludwig Schultz 1 — 1 IFW Dresden,
Institut fuer Metallische Werkstoffe, Postfach 270016, 01171 Dresden,
Germany — 2 TU Darmstadt, Institut fuer Physikalische Metallkunde,
Petersenstr. 23, 64287 Darmstadt, Germany
We report on the microstructure, the thermal stability and the mechanical
properties of slowly cooled Zr-Nb-Cu-Ni-Al alloys with ductile
bcc phase precipitates embedded in a glassy or nanocrystalline matrix.
The samples were prepared in form of rods by injection casting into a
copper mold. The phase formation and the microstructure of the composite
material were investigated by X-ray diffraction, EDX analysis and
scanning and transmission electron microscopy. The thermal stability
was examined by differential scanning calorimetry and the mechanical
behavior was investigated by compression tests under quasistatic loading
at room temperature. The formation of bcc phase dendrites and a glassy
or nanocrystalline matrix is strongly governed by the alloy composition
and the actual cooling rate during solidification. Besides, changes in composition
and cooling rate lead to different volume fraction and size of the
bcc phase precipitates and, hence, to different values of yield strength,
elastic and plastic strain. Illustrated by the presented results we show
the possibility of obtaining tailored mechanical properties by control of
composition and solidification conditions.
M 9.3 Mo 17:00 H16
Crystallization Behavior of Zr-Ti-Ni-Cu-Be type glasses — •s.
Mechler, N. Wanderka, and M.-P. Macht — Hahn-Meitner-
Institut Berlin, Glienicker Strasse 100, 14109 Berlin
The Zr-Ti-Ni-Cu-Be bulk metallic glasses belong to the best glassformers
and most stable glasses. However, the stability of the individual
glasses of this family depends on their composition. Accordingly
their crystallization behavior differs with composition and temperature
. To investigate these dependencies the crystallization behavior
of Zr41Ti14Ni10Cu12.5Be22.5 (V1), Zr46.8Ti8.2Ni10Cu7.5Be27.5 (V4) and
Zr50Ti5Ni10Cu10Be25 (V12) is studied by differential scanning calorimetry
(DSC), X-ray diffraction (XRD) and transmission electron microscopy
(TEM). Samples of the glasses were annealed isothermally at 643 K, as
well as after constant heating in the DSC with a rate of 4K/min. The
phase characterization from the XRD patterns is performed by use of
a Rietveld–Refining Procedure. During isothermal annealing icosahedral
quasicrystals form in V1 and V4. The quasicrystals are depleted of Be
and enriched in Ti. Mainly one crystalline phase, but no quasicrystals,
crystallizes in V12. After constant heating of the glasses up to higher
temperatures in the DSC only in V1 the first phase was quasicrystalline.
During further heating, these quasicrystals transform into a Laves phase,
whereas the remaining amorphous phase crystallizes into several phases,
like Be2Zr. During constant heating of the V4 and V12 glass mainly
a tetragonal phase crystallizes.The lattice constants of this tetragonal
phase alter systematically with increasing temperature. Simultaneously
to this alterations intermetallic phases appear in the microstructure.
M 9.4 Mo 17:15 H16
Zr-Nb-Cu-Ni-Al glass or nanocrystalline matrix composites
containing dendritic bcc phase precipitates — •Uta Kuehn,
Juergen Eckert, Nicolle Radtke, Norbert Mattern, and Ludwig
Schultz — IFW Dresden, P.O. Box 270016, D-01171 Dresden
This work presents results on the microstructure and the resulting mechanical
properties of the Zr66Nb13Cu8Ni6.8Al6.2 multicomponent alloy
with a glassy or a nanocrystalline matrix and ductile bcc precipitates.
This composite material was prepared by arc-melting, copper mold casting
and melt spinning with different sample dimensions and, therefore,
different cooling rates and microstructures. The structure of the samples
was investigated by XRD, OM, SEM, TEM and DSC. Room temperature
compression tests were realized with an electromechanical testing
device under quasistatic loading. The bulk samples exhibit significantly
improved mechanical behaviour compared to monolithic glass, since the
in-situ formed nanocrystalline matrix composites undergo work hardening
and plastic deformation prior to failure, whereas monolithic glass
forms highly localized shear bands, which consequently leads to catastrophic
failure. High ultimate compression stress combined with high
plastic strain is mainly dominated by a well-balanced ratio of the extant
phases. Surprisingly also a nanocrystalline matrix leads to high elastic
strain values. Illustrated by the composition presented in this study and
different cooling rates we show the possibility of obtaining tailored mechanical
properties for such composite materials.
M 9.5 Mo 17:30 H16
Quasicrystal Formation in Decomposed V4 Metallic Glass — •S.
Mechler, M. Wollgarten, N. Wanderka, and M.-P. Macht —
Hahn-Meitner-Institut Berlin, Glienicker Strasse 100, 14109 Berlin
The bulk metallic glass Zr46.75Ti8.25Ni10Cu7.5Be27.5 (V4) is one of the
most stable metallic glasses. The stability of this glass has been attributed
to a strong long range decomposition before crystallization occurs. In order
to characterize the first stages of crystallization and to relate the
crystallization to the decomposition of the glass, the early stages of these
phase transformations are investigated by means of differential scanning
calorimetry (DSC), X-ray diffraction (XRD), transmission electron microscopy
(TEM) and the 3-dimensional atom probe (3-DAP). After annealing
of the glass at 643 K for 6 h and at 593 K for 21 d an icosahedral
quasicrystalline phase is detected in the glass by XRD. After annealing
of the glass at 573 K for 42 d the alloy is still amorphous and a decomposition
of the initially homogeneous glass is observed by TEM and
3-DAP.Heating of such a decomposed glass in the DSC with a heating
rate of 4 K/min up to 709 K, leads to the formation of a icosahedral
quasicrystalline phase, which is different in composition and its quasilattice
constant from the quasicrystals after isothermal annealing. Even
after prolonged pre-annealing (84 d) at 573 K the alloy stays still amorphous
and also icosahedral quasicrystals form after the DSC treatment.
However, also these quasicrystals differ in composition and quasilattice
constants from both phases quoted above. One prominent feature of all
three quasicrystalline phases is their strong depletion of Be and enrichement
in Ti compared to the initial glass matrix.
M 9.6 Mo 17:45 H16
Atomare Struktur und Widerstand von amorphen
(In50Sb50)100−xAux — •Dirk Hauschild, Michael Lang
und Peter Häußler — TU-Chemnitz, Institut für Physik, D-09107
Chemnitz
In den letzten Jahren konnte festgestellt werden, dass amorphe und
flüssige Halbleiter / Halbleiterlegierungen duch ein Wechselspiel zwischen
dem Elektronensystem und der sich bildenden atomaren Struktur stabilisiert
werden. Man spricht dabei von einer Resonanz zwischen diesen
beiden Systemen. Wir berichten in dieser Arbeit über Messungen an
In50Sb50, bei dem wir durch Zulegieren von Gold den Durchmesser der
Fermikugel verkleinern. Wir untersuchen durch Elektronenbeugung und
durch Messung des spezifischen Widerstandes, wie sich dabei die atomare
Struktur anpassen kann und welche Konsequenzen dies für den elektr.
Transport hat. Die Ergebnisse werden zusammen mit anderen Halbleitersystemen
(reine Elemente und Legierungen) diskutiert. Die Schichten
wurden für diese Messungen in-situ bei 4K durch sequentielles Flashverdampfen
hergestellt. Sowohl direkt nach dem Aufdampfen, als auch
bei verschiedenen Temperstufen wurde die Struktur untersucht und der
Widerstand über den gesamten Temperaturbereich mittels Vier-Punkt-
Messung bestimmt.