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rapid
solidification
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Solidification
in conventional production processes such as casting occurs under
conditions close to thermodynamic equilibrium. At a solid/liquid
interface, equilibrium is generally adjusted within ca. 1µs, and
interface concentrations correspond to those in the equilibrium phase
diagram. However, materials properties can be enhanced by rapid
processes that do not allow equilibrium adjustment. In the Metallic
Materials group we process metals under extreme conditions: droplets
are levitated in an electromagnetic field and undercooled by several
100K. When solidifiation is triggered, front velocities of up to
>30m/s can occur, and metastable states will be found in the
samples.
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basic
research: solidification in microgravity
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Working out
the solution to some fundamental questions in the field of
solidification requires
well defined experimental conditions. Especially convection is a
process that adds complexity to transport processes and hinders the
interpretation of experimental results. In microgravity the influence
of convection can essesntially be suppressed, and physical effects can
be investigated in comparison with theory. At present, we plan to
conduct experiments on the International Space Station, concerned with
e.g. the following questions:
- what is the cooling rate at which an ordered crystalline state in an
intermetallic compound becomes disordered?
- what is the reasons that some alloys to not show an increasing
solidification velocity with increasing driving force?
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crystalline/amorphous
transition
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extreme solidfication conditions, solidification times can be so short
that atoms in the melt do not reach defined positions in a crystal
lattice. Amorphous alloys have been produced since ca. 1960, since 2015
we know that an amorphous state can also be generated in pure metals.
The mechanisms of the transition of crystalline to amorphous
solidification are a research topic of our group together with
colleagues of Udmurt State University i Izhevsk. |
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