Plenarvorträge - DPG-Tagungen

Metallphysik Donnerstag
M 23 Hauptvortrag Dieter Brunner
Zeit: Donnerstag 09:30–10:00 Raum: H16
Hauptvortrag M 23.1 Do 09:30 H16
Plasticity in body-centred cubic structures with emphasis on
low-temperature behaviour — •Dieter Brunner — Max-Planck-
Institut für Metallforschung, Heisenbergstrasse 3, 70569 Stuttgart
Materials crystallizing in the body-centred cubic (bcc) structure exhibit
plastic behaviour which differs impressively from that of differently
structured materials. The different behaviour is related to different slip
and work hardening mechanisms. The dependence of the yield stress on
temperature, strain-rate, and both the concentration and configuration
of atomic lattice defects is very pronounced in contrast to fcc materials.
These differences are particularly large in the low-temperature regime
below a characteristic temperature TK. At low temperatures, high purity
and sufficiently small sample dimensions are prerequisites for tensile
M 24 Nanoskalige Materialien III
tests. In the talk, relevant results of measurements with single crystals
of the metals α-Fe, Mo, W, Nb, Ta, the intermetallic alloy NiAl, the alkali
metal potassium, and the oxide ceramic SrTiO3 will be addressed.
The crucial point in the interpretation of the plasticity of bcc metals,
for example, is based on < 111 >a0/2 screw dislocations whose motion
governs the plastic behaviour and which possess a non-planar core structure.
Accordingly, they are rather sessile but can be moved by thermally
activated kink-pair formation on screw dislocations. Seeger’s kink-pair
theory developed in the 1980s has proved to be in excellent agreement
with the experimental results. Applying this model enables the macroscopic
behaviour to be described in terms of few kink parameters that can
be determined from deformation experiments for the above mentioned
materials.
Zeit: Donnerstag 10:15–11:15 Raum: H16
M 24.1 Do 10:15 H16
Melting behavior of Pb and In nanoparticles dispersed in AlYFe
matrix — •Nancy Boucharat, Harald Roesner, and Gerhard
Wilde — Forschungszentrum Karlsruhe, Institute of Nanotechnology,
Postfach 3640, 76021 Karlsruhe
Nanocomposites consisting of nanoscale Pb or In particles dispersed
within a crystalline Al matrix have attracted particular attention since
considerable deviations in the Pb and In melting temperatures have
been observed compared to that of the bulk. Beyond the nano-size effect,
several proposals involving contributions of the crystalline matrix
(e.g. grain boundaries, strains and defects, lattice orientation relationship)
have been advanced to account for the modified melting behavior.
Thus, the incorporation of Pb and In nanoparticles in marginal glass
formers gives a new opportunity to wider the understanding of the impact
of the matrix on the melting behavior, especially to study the sizedependent
melting behavior without the constraints imposed on the particles
by a crystalline matrix. Therefore, the melting behavior of Pb and
In nanoparticles embedded in rapidly quenched AlYFe glass have been
investigated by calorimetry and structural analyses. The results indicate
a general decrease of both melting temperatures. Moreover, the shift of
melting temperatures was found to be strongly correlated to the matrix
microstructure, i.e. whether the matrix is in an amorphous state, contains
Al-nanocrystal dispersions or is in a fully crystallised state.
M 24.2 Do 10:30 H16
Analysis of nanocrystalline CuBi-layers — •Daniel Wolde-
Giorgis, Talaát Al-Kassab und Reiner Kirchheim — Universität
Göttingen, Institut für Materialphysik, Tammanstraße 1, 37077 Göttingen
The segregation behaviour of Bi in nanocrystalline Cu-layers was investigated
by means of the tomographic atom probe (TAP) and field ion
microscopy (FIM). The investigated layers were prepared by sputter deposition
on W-substrates. These substrates have the shape of tips with a
radius of curvature of up to 60nm. Using a Kaufmann Ar-ionsource and
a deposition rate of 0.4 ˚A, we obtain a nanocrystalline CuBi-layer. FIM
analyses confirm the nanocrystalline structure of the deposited layers.
TAP analyses show an increased concentration of Bi. This value is about
two orders of magnitude higher than the solubility of Bi in Cu which
amounts up to 100ppm at 577K. A strong segregation at grain boundaries
is expected to occur while annealing. These supersaturated CuBi
alloys are therefore ideal model systems for the investigation of the microstructural
development.
M 24.3 Do 10:45 H16
Thermal reaction and stability of GMR Cu/NiFe thin films —
•Constantin Buzau Ene 1 , Guido Schmitz 2 , and Reiner Kirchheim
1 — 1 Tammann-Str. 1, D-37077 Göttingen — 2 Wilhelm-Klemm-Str.
10, D-48149 Münster
In recent years reading heads based on the giant magnetoresistance effect
(GMR) made possible a dramatic increase in magnetic recording density.
However, for many potential applications the thermal stability of the
magnetic multilayers are an important issue. In our study Cu/Ni79Fe21
(permalloy) multilayer stacks were deposited onto needle-shaped W tips
by ion beam sputtering and analyzed by atom probe tomography after
appropriate heat treatments. This analysis technique has been proven
to yield a real three-dimensional quantitative chemical and structural
analysis at a subnanometer scale.
After annealing at 250 ◦ C for 30min, no significant structural or chemical
transformation of the initial layer system is detected, although such a
heat treatment reduces the magnetoresistivity already appreciably. Clear
grain boundary wetting is observed after annealing at 400 ◦ C for 30min.
Further annealing at 500 ◦ C for 20min and 40min still preserves the layered
structure with a homogeneous solution of Ni inside the Cu layers of
up to 25 at.% Ni.
M 24.4 Do 11:00 H16
Strukturelle und magnetische Eigenschaften von Nd60Fe30Al10:
massive Proben, Splat-cooled und dünne Schichten — •A. Bracchi
1 , K. Samwer 1 , T. Niermann 2 , M. Seibt 2 und S. Schneider 2
— 1 I. Physikalisches Institut, Universität Göttingen, Tammannstr. 1, D-
37077 Göttingen — 2 IV. Physikalisches Institut, Universität Göttingen,
Tammannstr. 1, D-37077 Göttingen
Dünne Schichten, schnell abgekühlte Folien und massive Proben
der Zusammensetzung Nd60Fe30Al10 wurden mit unterschiedlichen
Präparationsmethoden hergestellt, wobei Abkühlraten zwischen 10 K/s
und 10 10 K/s erreicht wurden. Strukturelle und magnetische Eigenschaften
wurden mittels Hochenergie-Weitwinkel-Röntgen-Diffraktometrie,
Kleinwinkelneutronenstreuung (SANS), hochauflösender Elektronenmikroskopie
(HRTEM) und SQUID Magnetometer Messungen
untersucht. Die SANS Untersuchungen wurden mit und ohne Magnetfeld
durchgeführt, um den Kern-Beitrag von der magnetischen
Streuung zu trennen. Die Mikrostruktur zeigt ein fraktales Verhalten
mit Massen-Fraktaldimension zwischen 2.3 und 2.5, was auf eine
Phasenseparation in der unterkühlten Schmelze zurückgeführt werden
kann. Die Wechselwirkung von domain-wall-pinning Prozessen und
magnetischer Kopplung zwischen zwei unterschiedlichen magnetischen
Phasen wird diskutiert und die Abhängigkeit der Curietemperatur von
der Abkühlrate wird berücksichtigt, um das magnetische Verhalten der
massiven Proben und der Nd60Fe30Al10 Schichten zu erklären.
Gefördert von der DFG in Rahmen des SFB 602 (TP A5) und vom
Land Niedersachsen durch das “Georg Lichtenberg Programm”.