Technology Guide Principles – Applications – Trends - hhimawan

which is one of the strongest permanent magnetic materials)
but are very brittle. This is because chemical
ordering within the intermetallic phases does not allow
dislocations to move. Large intermetallic phase
parts are frequently manufactured by the powder metallurgy
method. In permanent magnets, the powder is
compressed within a magnetic field in order to align
the crystals orientation in a magnetic favourable direction.
Trends
7 High-temperature alloys.
The high-temperature
properties of nickel-based superalloys seem to be limited
by the melting point of nickel at 1455 °C. However,
these materials can withstand considerable stresses at
temperatures up to 1150 °C (over 80% of the melting
temperature). Much research is being carried out to
improve the temperature capabilities of these alloys.
Academic researchers are talking about the 4. and
5. generation of single-crystal nickel-based superalloys.
Despite tremendous efforts, there is no other material
in sight today that might be able to replace the
nickel superalloys within the next 10–20 years. This is
because these alloys have very well balanced properties,
which include ductility at all temperature levels,
combined with high strength at high temperatures.
These alloys also possess fairly good oxidation and fatigue
resistance. Special technical ceramics, alloys
based on platinum group metals (Pt, Rh, Ir), and other
high melting point systems such as Mo-Si are currently
under intensive investigation.
Another strategy for optimising the development
of high-temperature alloys is to reduce density and
production costs by keeping the high-temperature
strength at that level. This allows the overall weight of
the system to be significantly reduced by decreasing
the size of other load bearing parts. This is of specific
interest for moving or rotating parts as the rotating
speed can be considerably increased by using lowerweight
rotating parts.
These two optimisation strategies seem to point in
opposite directions, but both result in a comparable
technological improvement. Though at first sight apparently
different, both optimisation routes can be
found in practically all alloy developments based on a
specific application.
Prospects
5 Cost is an extremely important overall material
factor. Steels in particular can be produced in huge
quantities using low-cost production, forming and
molding processes. Steel will continue to make up
temperature [°C]
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5
2000
1500
1000
500
steels
a large part of car bodies in the near to medium
term, as well as – of course – being used as a
construction material. Particularly in view of the
increasing cost and shortages of raw materials, the
use of metals is becoming more widespread due to
cost considerations and very efficient recycling
possibilities.
The demand for light metals and high-temperature
metals to increase efficiency and reduce ecological
impact will go on increasing as long as man is technologically
minded. This applies to all kinds of
transportation systems from bicycles to airplanes
and energy production.
Researchers are currently striving to develop leadfree
solder alloys.
Rare earth and precious metals are very expensive
and only available in limited quantities, but are essential
and often not replaceable in many hightech
applications (e. g. energy-efficient lamps).
Prof. Dr. Uwe Glatzel
Dr. Rainer Völkl
Universitiy of Bayreuth
cross-section of a hollow turbine blade
gas temperature in military aircraft turbine engines
material temperature in civil aircraft turbine engines
polycrystalline
nickel-based superalloys
directional solidified
nickel-based
superalloys
gas temperature in civil aircraft turbine engines
improvement by
blade cooling
improvement
by materials
~5-10 K /year
single crystal
nickel-based superalloys
Internet
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5
5
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www.worldsteel.org
www.matweb.com
www.tms.org
www.mrs.org
material beyond
nickel-based
superalloys
1950 1960 1970 1980 1990 2000 2010 2020
year
� Increase in combustion gas temperature of aircraft turbine engines
over several decades – the efficiency of a turbine is closely
related to the gas temperature. After the Second World War, hightemperature
iron alloys with an upper limit of about 700 °C were
state­of­the­art materials. Nickel­based superalloys replaced iron
alloys in the 1950s and are still the material of choice today. Leaps
in technology meant that hollow turbine blades could be cast in
increasingly sophisticated designs, improving cooling efficiency.
Specifically designed nickel­based superalloys and adapted casting
technologies enabled the change to be made from polycrystalline,
to directionally solidified, to single­crystal turbine blades.
The gas temperature was increased by omitting the detrimental
interfaces between crystallites in single crystals. Due to the strong
safety standards in civilian aircraft engines, nickel­based superalloys
will not be replaced by ceramics in future. But insulation by a
thick ceramic layer is and will be of increasing importance.
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