Plenarvorträge - DPG-Tagungen

Metallphysik Mittwoch
M 22 Intermetallische Phasen
Zeit: Mittwoch 16:30–18:00 Raum: H6
M 22.1 Mi 16:30 H6
Ordering and Magnetism in Fe-Co: Quasi-Continuous Sequence
of Ground-State Structures — •Ralf Drautz 1 , Alejandro Diaz-
Ortiz 2 , Manfred Fähnle 3 , and Helmut Dosch 3 — 1 Department of
Materials, University of Oxford, OX1 3PH, UK — 2 Advanced Materials
Department, Instituto Potosino de Investigacion Cientifica y Tecnologica,
A.C., 78231 San Luis Potosi, S.L.P., Mexico — 3 Max-Planck-Institut
für Metallforschung, Heisenbergstraße 3, D-70569 Stuttgart
We have discovered that Fe-Co alloys develop a series of ordered
ground-state structures for different compositions additionally to the
known CsCl-type structure. This new set of ground-state structures was
found from a combinatorial ground-state search of 1.5 × 10 10 bcc-based
structures. The energies of the searched bcc structures were constructed
with the cluster expansion method from few first-principles calculations
for ordered Fe-Co structures.
To explain the sequence of ordered ground-state structures found in
FeCo, a hypothesis for the precondition to find a continuous sequence
of ground states in a binary alloy is proposed. In accordance with our
findings from the combinatorial ground-state search the system FeCo is
found to slightly violate the conditions for a continous ground state. This
naturally explains the found finite set of ground state structures.
M 22.2 Mi 16:45 H6
Magnetic Properties and Single Crystal Growth of the Er2PdSi3
intermetallic compound. — •Irina Mazilu 1 , Wolfgang Löser 1 ,
Günter Behr 1 , Kartik K Iyer 2 , P.L. Paulose 2 , E.V. Sampathkumaran
2 , and Ludwig Schultz 1 — 1 Leibniz-Institut for Solid
State and Materials Research Dresden, Helmholtzstr. 20, D-01171 Dresden,
Germany — 2 Tate Institute of Fundamental Research, Homi Bhabha
Road, Colaba, Mumbai-400005, India
Rare Earth (RE)- Transition Metal-Silicides are of general interest for
their magnetic and magnetoelectric properties and complex magnetic ordering.
Single crystals of Er2PdSi3 intermetallic compound with a hexagonal
AlB2 type crystal structure were grown by a floating zone method
with optical heating. The control of the oxygen impurity content was
the crucial point of crystal growth process. The preferred growth direction
was near [10-10]. The crystals exhibits an inferior depletion in Pd
and enrichment in Si with respect to the stoichiometric composition.
Growth relevant Er-Pd-Si phase diagram features have been revealed by
differential thermal analysis and additional microstructure investigations.
Magnetic measurement on oriented samples of Er2PdSi3 single crystals
exhibit antiferromagnetic order with a transition temperature at 7 K and
a relative small anisotropy compared to other RE2PdSi3, (RE=Tb,Ho).
However, anisotropic electrical properties as function of the temperature
were revealed. Neutron diffraction studies of the magnetic ordering are
in progress.
M 22.3 Mi 17:00 H6
Structural changes of TiAl deformed by high-strain torsion
— Guang-hui Cao, Werner Skrotzki, Carl-georg Oertel,
•Guang-hui Cao, Werner Skrotzki, and Carl-georg Oertel
— Institut fur Strukturphysik, Technische Universitat Dresden, 01062
Dresden, Germany
High-temperature extruded two-phase TiAl/Ti3Al intermetallics have
been deformed by torsion and their microstructures have been investigated
by transmission electron microscopy. The microstructural changes
observed consist of break-down of the lamellar structure and deformation
induced precipitation of TiAl3 and Ti2Al. The study is expected to
be helpful for understanding the relationship between the microstructure
and mechanical properties which can be changed drastically by highstrain
torsion.
M 22.4 Mi 17:15 H6
High-strain torsion of NiAl — •Burghardt Klöden 1 , Werner
Skrotzki 1 , Carl-Georg Oertel 1 , Roland Tamm 1 , Ulf Garbe 2 ,
and Erik Rybacki 3 — 1 Institut für Strukturphysik, Technische
Universität Dresden, 01062 Dresden, Germany — 2 DESY-HASYLAB,
Notkestraße 85, 22603 Hamburg, Germany — 3 Geoforschungszentrum
Potsdam, Telegrafenberg, 14473 Potsdam, Germany
High-temperature extruded polycrystalline NiAl, an intermetallic compound
with the B2-structure, has been deformed in torsion at temperatures
between 800K and 1300K in a Paterson-type rock deformation
machine under 400 MPa Argon confining pressure. The maximum strain
rate was about 10 −4 s −1 , the maximum shear strain about 15.6. Samples
with two different initial preferred orientations were deformed. With increasing
shear strain the shear stress goes over a maximum and reaches
a steady state value, indicating dynamic recrystallization. In addition, a
shortening of the torsion samples takes place (Swift effect). The results
will be discussed with respect to microstructure and texture formation.
M 22.5 Mi 17:30 H6
MODEL ALLOY BASED ON HIGH NI CONTAINING
MARAGING STEEL INVESTIGATED BY 3 DIMEN-
SIONAL ATOM PROBE — •Stefan Höring 1 , N. Wanderka 1 ,
J. Banhart 1 , H. Clemens 2 , and H. Leitner 2 — 1 Hahn-Meitner-
Institut Berlin, Glienicker Str. 100, 14109 Berlin — 2 Institut für
Metallkunde und Werkstoffprüfung, Montanuniversität Leoben,
Franz-Josef-Strasse 18, A - 8700 Leoben
The high Ni containing maraging steels are widely used for aerospace
as well for tools and dies because of their good mechanical properties.
The high strength of these steels is achieved by dispersion of precipitates
in nanometer scale. A model alloy based on the maraging steel
with the composition 75.08Fe-13.09Cr-8.38 Ni- 1.08 Si -0.96 Ti-0.69 Al
-0.57Mo-0.11 Mn -0.05 C (in at.%) was solution heat treated at 1273
K for 1 h and subsequently aged at 748 K for 12 h and 100 h. The microstructure
of the annealed specimens were studied by high resolution
methods such as three dimensional atom probe (3DAP) and high resolution
transmission electron microscopy (HRTEM). After 12 h annealing
time small precipitates of spherical morphology and of about 2 nm in diameter
were formed. They are enriched in Ni, Al, Ti and Si. After 100h
two additional phases were produced. One of them is enriched in Al, Ti
and Ni and the other one is mainly enriched in Cr.
M 22.6 Mi 17:45 H6
Three-dimensional finite element analysis of mismatch-induced
stresses and elastic strain energy distribution around precipitates
in INCONEL 706 alloy — •Vitaliy Kindrachuk, Nelia
Wanderka, Weiye Chen, and John Banhart — Hahn-Meitner-
Institut Berlin, Glienicker Str. 100, 14109 Berlin, Germany
The good mechanical properties of Inconel 706 up to 600 ◦ C are due to
strengthening by γ ′ , γ ′′ and γ ′ -γ ′′ precipitates. To better understand the
microstructure behaviour (the morphological and phase changes) during
the heat treatment is the stressed state on the interfaces of great interest.
The three-dimensional finite element (FE) analysis was used to investigate
the stress and strain energy features arising from a mismatch of
crystal lattices of coexisting phases.
The FE model was built based on characterization of the precipitates
and matrix by three-dimensional atom probe, high resolution transmission
electron microscopy, X-ray and synchrotron measurements. The precipitates
were modelled to have an oval morphology, negative misfit and
oriented parallel to the lattice direction of the γ matrix. The individual
precipitate variants of γ ′ ,γ ′′ and γ ′ -γ ′′ co-precipitates were analysed
under stress-free conditions. To obtain the long-range stress field we
have simulated the combination of precipitates taking into account their
mutual spatial arrangement. Prediction of the selective variant growth
was realized by addition the coupling between the applied stress and the
strain caused by the precipitates.