This
chapter highlights a comparative overview of the grain structure (especial the
CET) and the type of the coarsening process of the secondary dendrite arm
(especially the kinetic constant n) of the samples solidified in space and the
Earth to get information on the effect of buoyancy flow. During ground-based
solidification, buoyancy flow can develop by the density difference in the
hypoeutectic type of the alloy, such as Al-7 wt% Si alloy. Buoyancy flow can
affect the thermal field, solute distribution in the melt, and the position and
amount of the new grains. Under microgravity conditions, natural convection
does not exist or is strongly damped due to the absence of the buoyancy force.
Therefore, experiments in microgravity conditions provide unique benchmark data
for pure diffusive solidification conditions. Compared to the results of the
ground-based and microgravity ( µ g) experiments, it is possible to get
information on the effect of gravity (buoyancy force). In the framework of the
CETSOL project, four microgravity solidification experiments were performed on
grain-refined (GF) and non-grain refined Al-7 wt% Si alloy onboard the
International Space Station in the Materials Science Laboratory. Four
ground-based (GB) experiments were performed under Earth -like conditions with
the same (similar) solidification parameters in a vertical Bridgman-type
furnace. A detailed analysis of the grain structure and amount of eutectic and
secondary dendrite arm spacing (SDAS) for different process conditions is reported
and compared with the results of the microgravity experiments. GB experiments
showed that the microstructure was columnar in the samples that do not contain
GF material or in case the solid/liquid (vSL front velocity was slow (0.02
mm/s)). In contrast, in the GF material sample, progressive columnar/equiaxed
transition (PCET) was observed at vSL = 0.077 mm/s and GSL = 3.9 K/mm. The
secondary (SDAS) dendrite arm spacing follows the well-known power law, SADS =
K[ t0 ]1/3 where K is a constant, and t0
is the local solidification time for both GB and µg experiments. The
experiments in microgravity conditions provide unique benchmark data for pure
diffusive solidification conditions. Compared to the results of the
ground-based and microgravity experiments, it is possible to get information on
the effect of gravity (buoyancy force).
Author(s) Details:
András Roósz,
HUN REN- University of Miskolc, Materials Science Research Group,
Hungary and Institute of Physical Metallurgy, Metal Forming, and Nanotechnology,
University of Miskolc, Hungary.
Arnold Rónaföldi,
HUN REN-
University of Miskolc, Materials Science Research Group, Hungary and Institute
of Physical Metallurgy, Metal Forming, and Nanotechnology, University of
Miskolc, Hungary.
Yuze Li,
School of Physical Science and Technology, Northwestern
Polytechnical University, Xi’an, 710100, China.
Nathalie Mangelinck-Noël,
Aix Marseille University, Université de Toulon, CNRS, IM2NP, 13013
Marseille, France.
Gerhard Zimmermann,
ACCESS e.V., Intzestrasse 5, D-52072, Aachen, Germany.
Henri Nguyen-Thi,
Aix
Marseille University, Université de Toulon, CNRS, IM2NP, 13013 Marseille,
France.
Mária Svéda,
HUN REN- University of Miskolc, Materials Science Research Group,
Hungary.
Zsolt Veres,
HUN REN- University of Miskolc, Materials Science Research Group,
Hungary and Institute of Physical Metallurgy, Metal Forming, and
Nanotechnology, University of Miskolc, Hungary.
Please see the link here: https://stm.bookpi.org/EMMSMFMSA/article/view/13078