Plenarvorträge - DPG-Tagungen

Metallphysik Dienstag
tile (TiO2) single crystals with different orientations were investigated
by XRD and analytical TEM. BaTiO3 was found at the surface of the
reaction layer. It had a well-defined orientation relation to the rutile substrate.
In addition to BaTiO3, Ti-rich phases and pores were formed. This
observation is discussed by an outdiffusion of titanium and oxygen from
the BaTiO3-TiO2 interface. For a more detailed study of this behavior,
reaction couples of BaTiO3 thin films on rutile single crystal substrates
were prepared. Solid state reactions were initiated by heat treatment in
air. These experiments are compared with the BaO-TiO2 reaction.
M 18.9 Di 14:30 Saal C
Structure and reactivity at the Titanium-Silicon interface —
•Michael Schreiber, Igor Chaplygin, and Sibylle Gemming —
Institut für Physik, Technische Universität, D-09107 Chemnitz
The preparation of structurally and electronically well-defined interfaces
between metallic Ti and semi-conducting Si is complicated by the
formation of crystalline and amorphous binary compounds with a wide
compositional range. Molecular-dynamics density-functional calculations
[1] are carried out for the prototype interface Ti(0001)—Si(111), where
Ti5Si3, TiSi, and TiSi2 phases were observed experimentally. In accordance
with those results, the first steps of the compound formation show
that an amorphous film is accessible at temperatures, for which the crystalline
binary compounds do not yet exhibit melting. The interface reaction
is accompanied by an equilibration and reduction of the stress
tensor components, which are present in the atomically flat interface due
to the lattice mismatch between Si(111) and Ti(0001). Thus, the silicide
formation is not only driven by the electronegativity difference of Ti and
Si, but enhanced by an elastic contribution. [1] www.abinit.org
M 18.10 Di 14:30 Saal C
Positronenspektroskopische Untersuchung von Magnesiumdruckgusslegierungen
mit einem Koinzidenz-Doppler-
Spektrometer — •Christoph Hugenschmidt und Martin
Stadlbauer — Physikdepartment E21, Lichtenbergstraße 1,
Technische Universität München, 85747 Garching
Leichtmetalllegierungen auf Magnesiumbasis spielen insbesondere aufgrund
des niedrigen spezifischen Gewichts eine herausragende Rolle. Legierungsbestandteile
wie Aluminium und Zink der in der Automobilindustrie
am häufigsten verwendeten Legierung AZ91 verbessern die mechanischen
Eigenschaften, die Korrosionsbeständigkeit sowie die Giesseigenschaften.
Druckgussproben dieses Materials unterschiedlicher Porosität
sowie thermisch behandelte Proben wurden mit der Positronenspektroskopie
studiert. Hierzu wurden mit einem Koinzidenz-Doppler-
Spektrometer unter Verwendung einer 22 Na-Quelle hochauflösende Messungen
der 511 keV - Annihilationslinie durchgeführt. Die nahezu untergrundfreien
Messungen lassen eine Linienformanalyse des Hochimpulsanteils
im Bereich grö¨ser 513 keV zu, wodurch man Impulsinformation
über die an der Zerstrahlung beteiligten Rumpfelektronen erhält. Die
hierdurch mögliche Elementspezifizierung in der Ungebung von Fehlstellen
wird diskutiert.
M 18.11 Di 14:30 Saal C
Resistometric investigations of ”order-order”kinetics in intermetallics
with varying superstructure stability — •Ewa Partyka
and Rafal Kozubski — M. Smoluchowski Institute of Physics,
Jagiellonian University, Reymonta 4, 30-059 Krakow, Poland
Investigations of long - range ordering kinetics in ternary intermetallic
systems of superstructure L12 were carried out. Two groups of compounds:
Ni75Al25−xFex and Pt75Co25−xFex , showing opposite relationships
between the stability of L12 superstructure and concentration of
Fe, were examined by means of isochronal residual resistivity.
The effect has been analyzed within the Schulze- Lücke formalism [1]
enabled separate estimation for vacancy formation EF and migration
EM energies being components of the overall activation energy EA for
ordering kinetics. It was found out that in both systems an increase of
activation energy EA accompanying an increase of L12 superstructure
stability is due the increasing tendency of the vacancy formation energy
EF, the activation energy for vacancy migration EM shows either
week decrease with x (Pt75Co25−xFex) or no Fe-concentration dependence
(Ni75Al25−xFex).
References:
[1] Schulze A, Lücke K. Acta Metall 1972;20:529.
M 18.12 Di 14:30 Saal C
Berechnung wahrer Teilchengrößenverteilungen aus Schnittbildern
— •Jürgen Gegner — SKF GmbH, Werkstoff-Physik, Ernst-
Sachs-Str. 5, D-97424 Schweinfurt
Partikelverteilungen innerhalb einer metallischen Matrix, die etwa bei
Ausscheidungsreaktionen oder innerer Oxidation entstehen, werden zumeist
durch licht- oder rasterelektronenmikroskopische Schliffaufnahmen
charakterisiert. Da bei einem solchen Flächenschnitt ein bestimmtes Teilchen
im Allgemeinen nicht zentral, sondern an einer beliebigen Position
geschnitten wird und die Wahrscheinlichkeit für seine Erfassung mit der
Ausdehnung zunimmt, weicht die Größenverteilungen in der Schnittebene
von der gesuchten wahren Größenverteilung im Volumen ab. Die notwendige
Umrechnung erfordert eine stereologische Analyse. Im vorliegenden
Beitrag wird hierfür ein mathematisches Korrekturverfahren abgeleitet
und diskutiert. Ein Computerexperiment mit 20000 statistisch verteilten
Kugelobjekten, deren Größen einer für natürliche polydisperse Partikelsysteme
typischen Lognormalverteilung gehorchen, bestätigt die Anwendbarkeit
der Methode. Die Verschiebung der aus dem Flächenschnitt
entnommenen Größenverteilung hin zu kleineren Durchmessern wird zutreffend
vorhergesagt. Das stereologische Analyseverfahren wird exemplarisch
auf ein diskontinuierliches Dualphasengefüge angewandt.
M 18.13 Di 14:30 Saal C
Evaluation of Carbon Diffusivities in Steels from
Concentration-Distance Curves with Phase Transformation
by Finite Element Analysis — •Jürgen Gegner — SKF
GmbH, Material Physics, Ernst-Sachs-Str. 5, D-97424 Schweinfurt
Application of the isothermal Rhines pack decarburization technique
for the determination of composition-dependent diffusion coefficients of
carbon in the austenite phase of low-alloyed steels at common austenitising
temperatures between 1070 and 1170 K results in an austenite-ferrite
phase transformation in the edge zone of the sample caused by the carbon
loss. This is shown by the concrete example of through-hardenable
rolling bearing steel SAE 52100 (German denotation: 100Cr6) annealed
at 1123 K for 5 h, where the decarburization profile is measured with
high accuracy and spatial resolution by secondary ion mass spectrometry.
Due to the phase transformation, a modified Matano analysis cannot
be applied. Thus, a FE code is developed that permits data fitting by automatized
profile simulation. This way, the carbon diffusivity in austenitic
SAE 52100 is derived from the measuring curve. The obtained result is
compared with literature data on binary Fe-C and ternary Fe-Cr-C.
M 18.14 Di 14:30 Saal C
Determination of Mechanical Characteristics of Adhesively
Bonded Metal Joints by Experiment and Finite Element Data
Analysis — •Jürgen Gegner 1 and Andreas Öchsner 2 — 1 SKF
GmbH, Material Physics, Ernst-Sachs-Str. 5, D-97424 Schweinfurt —
2 University of Aveiro, Department of Mechanical Engineering, Campus
Universitário de Santiago, 3810-193 Aveiro, Portugal
In all fields of industry, modern adhesives are in a position to costeffectively
join metal parts into complex components for e.g. structural
bonding or sealing applications. Thus, computer-aided product design
requires in situ determination of mechanical parameters. The thickadherend
tensile-shear test has established itself as the most important
destructive testing method in adhesive technology. In the present work,
this technique is improved relative to the standard ISO 11003-2 in the experimental
and evaluation part. Stepped metal substrates ensure a more
uniform stress state by increasing the stiffness of the assembly. The total
displacement of the joint is measured directly at the overlap zone to minimize
the influence of adherend deformation, which is considered by the
numerical analysis of a dummy sample. Test evaluation is extended by a
finite element simulation technique that additionally allows derivation of
Young´s modulus from measured shear stress-strain curves. As concrete
examples, steel and aluminum substrates were tested at various temperatures
applying anaerobic and silicon adhesives with different bond gaps.