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(> 5 m/s MRV) at a collision model
(> 9 m/s up to 14 m/s MRV) resulting in
processing times ranging from seconds
to minutes to a few hours at maximum
resulting in low contamination levels
in respect of the processing tools. As
for the oxygen pick-up, the equipment
must provide a process under completely
protected conditions (inert gas
or vacuum) which must cover charging
(loading), processing and discharging
(unloading).
Potential passivation after discharging
can be an important issue as well and
the entire process cannot exhibit any
dead-zones. This is what Zoz GmbH is
providing and applying.
Third and fourth secret:
HEM and HRS
One interesting example for the use of
the high energy milling (HEM) under
the protection of inert gas was given by
Prof. Cai Xiaolan, University of Science
and Technology, Kunming, Yunnan,
with the preparation of Zinc-flakes by
High Energy Milling.
The increase of strength was also
topic of the presentation of Tatsuya
Sekiguchi, Ritsumeikan University. In
this investigation pure titanium powder
and a Ti-6Al-4V alloy powder are
treated by mechanical milling (MM),
which is one of the severe plastic deformation
(SPD) processes. The MM
process enables the production of a
nano grain microstructure very easily
Discussion during the poster session
216
and has been applied to many powder
materials. They are then sintered
by hot roll sintering (HRS). The MM
powders have a nano grain structure
with grain size of about 50 nm at the
surface region and have a work hardened
microstructure in the core region
of the powder. The HRS compacts have
a harmonic microstructure that consists
of a nano grain structure with a
grain size of 200 to 500 nm and a coarse
martensite structure. The pure titanium
and Ti-6Al-4V HRS compacts indicate
superior mechanical properties.
The HRS compacts indicate a good
elongation compared to conventional
heavily deformed materials. “The HRS
process is very effective to the improvement
of mechanical properties in the
pure titanium and Ti-6Al-4V alloy.”,
the speaker concluded.
Secret No. 5: Very fine powders
Takeshi Fukuda, Fukuda Metal Foil &
Powder Co., Japan, spoke about diameter
control of stamped powder. He
said that his company is producing a
lot of different metal powders for several
applications, for example for the
automotive industry and engineering.
The speaker showed interesting examples
of sintering parts, made out of copper,
bronze – combined with diamond
or carbon. In such cases bronze powder
is acting as a binder. In a video the
speaker showed how fine powders are
floating in a stamp mill. He discussed
methods for achieving a very fine distribution.
Prof. Nobuhiro Tsuji, Kyoto University,
Japan, spoke about the unique
microstructures and mechanical
properties of nanonstructured metals
fabricated by severe plastic deformation.
Ultrafine grains or nanocrystals
are much smaller than 1 μm, that
means the volume fraction of grain
boundaries quickly increases. (For
comparison: the conventional grain
size ranges from 1 to 100 μm). The
severe plastic deformation (SPD) was
carried out as a rolling process (ε > 4),
called ARB (accumulated rolling
bonding), developed by the author.
Several materials were examined, for
example carbon steels, stainless steels,
Al-alloys, OFHC-Cu, Cu-Co-P and
some others. The determination of
the microstructure was carried out
by an TEM Kikuchi lines misorientation
analysis. It shows, the most of
the boundaries were high angle grain
boundaries, but in a very low grain
size. The mechanical properties are
impressive: For aluminium a tremendous
strength was achieved.
Secret No. 6: Nanoclusters
Prof. Dr. Brian Wirth, University of
California Berkeley, USA, spoke about
atomic scale investigations of Y-Ti-Onanoclusters
in nanostructured ferritic
alloys. He told the audience that
nanostructured ferritic alloys (NFAs)
are characterized by very high tensile
and creep strength at temperatures
of 650 °C and above, and remarkable
resistance to neutron irradiation effects.
These properties result from a
very high number of density dispersions
of nm-scale Y-Ti-O rich features
(NFs) that precipitate homogeneously
at high consolidation temperatures
from mechanically alloyed Fe-Cr-Ti-
Y 2 O 3 powders. NFs form rapidly at a
number of densities, sizes and characters
(compositions and structures) that
are primarily dictated by the processing
temperature history and alloy composition.
However, the precise natures
of various NFs are not yet well understood,
and they appear to range from
coherent solute enriched GP-type
zones to near stoichiometric complex
5/2009 | 63. Jahrgang | METALL