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Актуальные семинары
Семинар № 152 (15.11.2018)
Научно-исследовательский технологический институт (НИТИ) Ульяновского государственного университета (УлГУ)

Main obtained results

 

  • Mechanical properties of the irradiated specimens and particularly that of ARBOR 2 have been investigated by FZK in cooperation with A. Povstyanko (RIAR) group in impact and tensile tests within the ISTC project 2781p. The neutron irradiation induced hardening and embrittlement have been quantified in terms of the shifts in the yield stress and DBTT. The observed saturation of the irradiation induced hardening and embrittlement at the achieved doses of 70 dpa has been phenomenologically described.
  • KIT performed quantification of helium induced hardening and embrittlement through the analysis of the mechanical properties of boron doped heats after neutron irradiation in SPICE, ARBOR 1 and ARBOR 2 irradiation programmes. Based on these results the estimation of He & DPA effects for DEMO relevant helium production rate was performed. After post irradiation annealing experiments the boron doped heats showed larger residual embrittlement and hardening compared to reference RAFM steel which was attributed to helium effects.
  • Molecular dynamics simulation of atomic displacement cascades up to 20 keV has been performed in Fe–10 at.%Cr binary alloy at a temperature of 600 K. The N-body interatomic potentials of Finnis–Sinclair type were used. According to the obtained results the dependence of ‘‘surviving” defects amount is well approximated by power function that coincides with other researchers’ results. Obtained cascade efficiency for damage energy in the range from 10 to 20 keV is ~0.2 NRT that is slightly higher than for pure a-Fe. In post-cascade area Cr fraction in interstitials is in range 2–5% that is essentially lower than Cr content in the base alloy. The results on size and amount of vacancy and interstitial clusters generated in displacement cascades are obtained. For energies of 2 keV and higher the defect cluster average size increases and it is well approximated by a linear dependence on cascade energy both for interstitials and vacancies.
  • The thermodynamic and kinetic models of cluster formation in binary alloys under thermal ageing have been developed in this work. Thermodynamic analysis of Fe–Cr in terms of Gibbs free energy minimization method revealed that the interphase surface energy is one of the main factors determining the cluster composition. The models were applied to describe the Cr nanocluster formation in Fe–20Cr binary alloy under thermal ageing at 773 K. The calculation of energy characteristics of Cr-rich clusters is performed in terms of molecular statics method by using many-body classic potential which describes well complex formation energy curve of Fe–Cr alloy. According to the numerical solution of Fokker–Planck equation the description of the growth kinetics of nanoclusters in Fe–20Cr has been performed. It was shown that the clusters growth may be satisfactorily explained in terms of the diffusion model.
  • The atomic displacement cascades in Fe–9 at % Cr and Fe–9 at % Cr–0.1 at % C alloys are studied by molecular dynamics simulation at an initial temperature of 600 K. The average fractions of defects that “survive” in a displacement cascade are calculated for primary knocked-on atom (PKA) energies of 0.1–20 keV, and the number and size of the vacancy and interstitial atom clusters that form in a displacement cascade are determined. Carbon at the concentration under study is found not to affect the number of survived defects and the cascade efficiency. At PKA energies of 15 and 20 keV, the presence of carbon slightly decreases the fraction of point defects forming clusters.
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  • Quantitative TEM investigation of neutron irradiated EUROFER97 from WTZ and ARBOR 1 were performed by O. J. Weib (KIT). Quantitative analysis of 15 and 32 dpa irradiated samples was fulfilled. Radiation induced hardening due to dislocation loops was estimated.
  • The microstructure of EUROFER97 neutron-irradiated to a high-dose of 31.8 dpa was analyzed quantitatively by means of WBDF microscopy. Irradiation induced defects like small point defects clusters dislocation loops sized between 1 nm and 25 nm have been detected. The average size was 4.9 nm. The average volume density of visible defects was 1.75´1022 m-3.
  • A phenomenological model based on kinetic rate equations is developed to describe homogeneous nucleation and growth of helium bubbles in neutron irradiated RAFM steels. This model is realized as FORTRAN computer code. The model is adapted to different 10B doped EUROFER97 based heats, which already had been studied in past irradiation experiments. Simulations yield bubble size distributions, whereby effects of helium generation rate, surface energy, helium sinks and helium density are investigated. Peak bubble diameters under different conditions are compared to preliminary microstructural results on irradiated specimens. Helium induced hardening was calculated by applying the Dispersed Barrier Hardening model to simulated cluster size distributions.
  • Modelling of formation of second phase particles in alloys based on Fe-XCr (X=10, 12, 14, 16 at%) based on the proposition of radiation-enhanced diffusion was performed. The developed model allows making quantitative conclusions about cluster and matrix composition change under neutron irradiation and also to calculate the dependence of average size and cluster concentration on damage doses up to 10 dpa for Fe-Cr alloys of different compounds. The calculations correspond to the experimental data of other authors on the character of microstructural changes on the early stage of irradiation for the damage dose of 0.6 dpa. The diffusion coefficient of Cr atoms under irradiation is equal 1.4´10-15 sm2/s. That is seven orders of magnitude higher than thermal diffusion coefficient at the temperature of 300C.
  • The results of MD simulation of the atomic displacement cascades with the PKA energy of 15 and 20 keV in a Fe-9at.%Cr crystallite containing a spherical Cr-rich cluster with the diameter range from 1 to 5 nm were obtained. Simulations are performed at 300K using modified version of N-body interatomic potential proposed by A. Caro et al. We have shown that this potential gives a reasonable agreement with ab initio data for the binding energy of Cr atoms with different defects in the bcc Fe matrix. The parameters of the primary damage state have been obtained for the systems with and without a Cr-rich cluster. It is stated that the 5 nm cluster provokes the rise of survived defects in the 15 keV cascades by ~25%. A small increase of Cr fraction in SIA defects has been registered for the cascades initiated at the short distance (up to 5.08 nm) from the 5nm cluster. The 1 nm cluster has not considerable effect on the primary radiation damage. The main obtained result is the dissolution of small Cr precipitates (1nm) directly in PKA cascades. While, large precipitates (with the diameter of 3-5nm) exhibit only slight modifications and can be considered as stable. On the contrary, the composition and size of small (1nm) clusters change considerably, up to their complete dissolution. Notable decrease of Cr fraction can occur in medium 2 nm clusters without their total dissolution.

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Papers

  1. M. Tikhonchev, V. Svetukhin, A. Kadochkin, E. Gaganidze, MD simulation of atomic displacement cascades in Fe–10 at.%Cr binary alloy, Journal of Nuclear Materials 395 (2009) p. 50–57.
  2. М. Ю. Тихончев, В. В. Светухин, А. С. Кадочкин, Э. Гаганидзе. Первичная радиационная повреждаемость сплава Fe-10%Cr: моделирование методом молекулярной динамики. Тезисы докладов IX Российской конференции по реакторному материаловедению, Димитровград, 14 – 18 сентября 2009 г., с. 167 – 170.
  3. C. Dethloff, E. Gaganidze, V. Svetukhin, M. Tikhonchev, O. Wei, J. Aktaa, Modeling of helium bubble formation and growth in RAFM steels under neutron irradiation, Extended Abstracts Book of First International Conference on Materials for Energy, Karlsruhe, Germany, July 4 – 8, 2010, p. 196 – 198
  4. V. Svetukhin, P. L’vov, E. Gaganidze, M. Tikhonchev, C. Dethloff, Kinetics and thermodynamics of Cr nanocluster formation in Fe-Cr system // Journal of Nuclear Materials, 415, 2011, pp. 205 – 209
  5. M. Yu. Tikhonchev, V. V. Svetukhin, A. S. Kadochkin, and E. Gaganidze. Molecular Dynamics Simulation of Atomic Displacement Cascades in Fe–9 at % Cr and Fe–9 at % Cr–0.1 at % C Alloys // Russian Metallurgy (Metally), 2011, No. 5, pp. 415–422
  6. P. E. L’vov, V. V. Svetukhin, and A. V. Obukhov, Thermodynamics of Phase Equilibrium of Binary Alloys Containing Nanoprecipitates, Physics of the Solid State, 2011, Vol. 53, No. 2, pp. 421–427
  7. C. Dethloff, E. Gaganidze, V. Svetukhin, J. Aktaa, Modeling of helium bubble nucleation and growth in neutron irradiated boron doped RAFM steels // Journal of Nuclear Materials, 2012 (in press)

 

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