and Validation Experiments for Atomistic Modeling of FeCr Alloys
– Ion Irradiation, Analysis at the Nanometer Scale, Determination of Specific Physical Materials Properties –
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.