Plenarvorträge - DPG-Tagungen

Metallphysik Donnerstag
M 31 Quasikristalle II
Zeit: Donnerstag 16:30–18:00 Raum: H16
M 31.1 Do 16:30 H16
Decagonal quasicrystals in the Al-Pd-Re alloy system —
•Sergiy Balanetskyy 1,2 and Benjamin Grushko 1 — 1 IFF,
Forschungszentrum Juelich, D-52425 Juelich — 2 I.N. Frantsevich
Institute for Problems of Materials Science, 03680 Kiev 142, Ukraine
The Al-Pd-Re alloy system is known to contain a stable icosahedral
phase similarly to that in Al-Pd-Mn (Mn and Re belong to the same
column in the periodic table). Apart from this, Al-Pd-Mn contains a
decagonal phase with about 1.2 nm periodicity in the specific direction.
Extensive investigation of the Al-rich part of the Al-Pd-Re phase diagram
revealed the formation of a decagonal phase also in this alloy system. In
contrast to that in Al-Pd-Mn the Al-Pd-Re decagonal phase has about
2.4 nm periodicity. Preliminary investigation of this phase and its formation
conditions will be reported.
M 31.2 Do 16:45 H16
Formation and stability of the Al-Cu-Ru icosahedral phase —
•Benjamin Grushko and Shaobo Mi — IFF, Forschungszentrum
Juelich, D-52425 Juelich
The Al-Cu-Ru icosahedral (I) phase is formed in a wide compositional
range elongated between about Al61Cu26Ru13 and Al70.5Cu12.5Ru17.
The powder X-ray diffractograms only revealed some variation in the
intensities of the lines as a function of the composition but no their apparent
shift. The I-phase is formed by a peritectic reaction at 1057 C,
its stability was confirmed down to 600 C. At lower temperatures the
equilibration of the relevant samples is difficult. Extrapolated towards
lower Cu the I-region clearly reaches the binary composition of about
Al78-80Ru20-22. At close compositions a similar I-phase has also be reported
to form in rapidly solidified alloys. The elongated geometry of
the stability region is consistent with a suggestion that the ternary Al-
Cu-Ru I-phase is a solid solution of Cu in a metastable binary Al-Ru
I-phase. The shape of the I-region corresponds to an approximately constant
electron-to-atom ratio.
M 31.3 Do 17:00 H16
Influence of Al and Zr on quasicrystalline phase formation in Zr-
Ti-Nb-Cu-Ni-Al metallic glasses — •Sergio Scudino 1 , Jürgen
Eckert 2 , Uta Kühn 1 , Hergen Breitzke 3 , Klaus Lüders 3 und
Ludwig Schultz 1 — 1 IFW Dresden, Institut für Metallische Werkstoffe,
Postfach 270016, D-01171 Dresden, Germany — 2 Fachbereich
Material- und Geowissenschaften, FG Physikalische Metallkunde, Technische
Universität Darmstadt, Petersenstrasse 23, D-64287 Darmstadt,
Germany. — 3 Fachbereich Physik, Freie Universität Berlin, Arnimallee
14, D-14195 Berlin, Germany
The influence of Al and Zr on the crystallization behavior of Zr-Ti-Nb-
Cu-Ni-Al melt-spun glassy ribbons with different Al and Zr content have
been investigated. The devitrification is characterized by the formation of
a quasicrystalline phase even for the alloy without Al, demonstrating that
Al is not essential for quasicrystal formation in the present alloys. With
decreasing Al content, the temperature range of stability of quasicrystals
increases whereas the thermal stability of the amorphous phase decreases
together with a slight decrease of the extension of the supercooled liquid
region. Furthermore, the grain size of the quasicrystalline phase increases
with decreasing Al content. An equivalent effect on both thermal stability
and microstructure can be achieved by increasing Zr content. This
suggests the possibility to use Al and Zr for tuning the thermal stability
as well as the microstructure evolution upon heating. This work was supported
by the German Science Foundation under grants Ec 111/10-1,2
and Lu 217/17-1
M 31.4 Do 17:15 H16
Micro-and nanoindentation studies of single quasicrystalline
phase in Al-Ni-Co system — •Nilay Krishna Mukhopadhyay,
Andre Belger und Peter Paufler — Institut fuer Strukturphysik
TU Dresden, D-01062 Dresden, Germany
Single crystals of Al-Ni-Co decagonal phase have been employed for
the study of mechanical propertied using the micro- and nano- indentation
techniques. Decagonal quasicrystal gives rise to decagonal prismatic
morphology exhibiting 10-fold and 2-fold planes as external facets. The
microindentation, using load from 25g to 150g was performed on 10 fold
and 2-fold planes. Meyers Hardness calculated from these studies was
found to vary from 13.3GPa to 10.6GPa. The variation of hardness with
load, which is known as indentation size effect (ISE), was clearly noticed.
Nanoindentation experiments were carried out using Hysitron Triboscope
attached to scanning probe microscope. From load-penetration
curve nanohardness and elastic modulus were found out and compared
with the data available from other techniques. The discontinuity in the
load-penetration curve, which can be understood as pop-in-effect, characteristic
of yielding, was observed at low load regime. It is interesting to
point out that the pop-in effect is more prominent in case of 10fold plane.
Attempts will be made to discuss the results obtained from the present
investigation in the light of our current understanding of the mechanical
responses of these aperiodic crystals.
M 31.5 Do 17:30 H16
Hydrodynamic excitations of icosahedral quasicrystals —
•Christof Walz and Hans-Rainer Trebin — Universität
Stuttgart, Institut für Theoretische und Angewandte Physik, 70550
Stuttgart
Hydrodynamic variables for quasicrystals are, aside from mass-,
momentum-, energy-density, and phonon displacements, also phason displacements,
at least in certain temperature ranges. Different derivations
of the hydrodynamic equations exist, either on a phenomenological basis
or by Poisson bracket methods, which we have compared and checked.
They were solved numerically for special boundary and initial conditions
to mimic experiments like internal friction. We also derived material
laws of anelasticity from the hydrodynamic equations to model relaxation
mechanisms directly.
M 31.6 Do 17:45 H16
chains of 2 n interpenetrated icosahedra in hexagonal
Zn-Mg-RE (Y, Sm, Gd) phases — •D.W. Deng 1,2 ,
K.H. Kuo 2 , M. Feuerbacher 1 , and K. Urban 1 — 1 Institut für
Festkörperforchung, Forschungszentrum Jülich GmbH, D-52425 Jülich,
Germany — 2 Beijing Laboratory of Electron Microscopy, Institute of
Physics, Chinese Academy of Sciences, PO Box 603, 100080 Beijing, PR
China
The crystal structure of the hexagonal Zn3MgY phase has been determined
by single-crystal X-ray diffraction. The structural model, refined
to a final R value of 0.047, has the composition Zn60.68Mg18.28Y21.04,a
= 9.082(2) ˚A and c = 9.415(5) ˚A and the space group P63/mmc. The
structure of Zn3MgY is characterized by a layer structure consisting of
FP(FP)’ layers stacked along the c axis, where F and P denote flat and
puckered layers, respectively, and (FP)’ is related to FP by a 63 screw.
The Zn3 icosahedra, in the PFP’ layer block are fused into pairs in the
directions. At the same time, the hexagonal Zn3MgY phase is
known to consist of 2 interpenetrated Zn icosahedra along directions.
This can be considered as the fundamental period (n = 1) of a
series of 2n super-periodic icosahedral chains. The hexagonal S, M, and
L or µ3, µ5, and µ7 phases of larger a parameters are found to have superperiodic
chains containing 2n = 4, 6, and 8, respectively, interpenetrated
icosahedra in directions. The estimated periodicity of this series
of super-periodic 2n (n = 2, 3 and 4) interpenetrated icosahedral chain
agrees with most cases of the experimental a parameter of the hexagonal
S, M, and L or µ3, µ5, and µ7 phases.