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Workshop on Multiscale Modeling of FeCr Alloys Brussels,
14-15 March 2005
Abstract
Verification
and Validation Experiments for Atomistic Modeling of FeCr Alloys
–
Ion Irradiation, Analysis at the Nanometer Scale, Determination of Specific
Physical Materials Properties –
M. Rieth
Forschungszentrum
Karlsruhe, Institut für Materialforschung I, P.O. Box 3640, 76021 Karlsruhe
Modeling irradiation
effects in fusion relevant materials is a key issue of the European Fusion
Program. Both, analytical and computer simulation of different physical
processes have extensively evolved during the last decade to cover several
orders of magnitude of both spatial and time scales. Furthermore, by coupling sequentially
methods applicable to each scale, it has been shown that the evolution of very
complex physical phenomena can be described in a predictive way. The major
goals are to establish models within a multiscale framework that are validated
experimentally and develop a predictive capacity. These have to simulate fusion
relevant conditions in the temperature range from RT to 550 °C in the presence
of high concentrations of irradiation induced impurities (e.g. H, He). In this
connection, emphasis needs to be given to the experimental validation of the
simulations using model alloys as well as real RAFM alloys like EUROFER. A
number of critical points, some of which were already noticed at the start of
the program, need still to be solved: (i) the bcc Fe potential and its use in
molecular dynamics, (ii) ab-initio calculations studying the effect of C on the
interaction of He and vacancy clusters, (iii) Monte Carlo simulations on the
evolution of He in the Fe-C and Fe-Cr systems, (iv) irradiations of Fe-Cr (model)
alloys made of high purity components to study defect accumulation and to look
at segregation and overall alloy stability between 350 and 400 °C. Therefore,
in the near future emphasis has to be given to verification and validation of
the recently developed tools. At the Institute for Materials Research I
(IMF-I), Forschungszentrum Karlsruhe, different according activities have been
started which are briefly outlined in the following. In collaboration between IMF-I
and HMI Berlin an ion irradiation program will be performed in 2005 to validate
present modeling results and to provide further information about the
microstructural evolution of irradiation induced defects. IMF-I will produce
and provide pure Fe, Fe12%Cr, and Fe15%Cr single crystal specimens (diam. 3 mm,
thickn. 0.5 mm, <100>, <110>, and <111> orientation) for
irradiation. After irradiation parts of the specimens will be transported to
the FZK for preparation and following TEM and FEGSTEM examinations. Atomic
Probe Investigations will be performed at HMI. The examinations may provide specific
information on size and density distribution/mobility of loops/clusters as well
as on chemical composition at the border of loops, Cr-loop interaction, and He
bubbles morphology. Until today there is still a lack of physical and mechanical
data for Fe-Cr single crystals with a low Cr content. But it would be most
desirable for the development Fe-Cr potentials to know the real elastic
constants and thermal expansion coefficients. These data could be directly used
to adjust the according fits. Therefore, two Fe-Cr single crystals with 15% and
12% Cr will be used to determine elastic constants and thermal expansion and/or
thermal conductivity. Young’s modulus will be determined at RT with compression
tests and thermal properties will be measured with calorimetric equipment. The
data will be produced for two different orientations each. Another, but
computationally extensive validation procedure is the comparison of load curves
from nanoindentation tests with those from large scale model MD simulations.
Nanoindentation tests may be preformed, again, on slices of Fe-Cr single
crystals with different orientations. Then, an according model has to be
developed and adapted to the testing equipment.
557 words