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  1. Thermal annealing influence on ions implanted Fe-Cr model alloysS. Sojaka, , V. Slugeňa, V. Kršjakb, W. Eggerc, L. Ravellic, M. Petriskaa, S. Stančeka, M. Skarbad, P. Priputend, K. Vitázeka, M. Stachoa, J. Veterníkováa, V. SabelováaaInstitute of Nuclear and Physical Engineering, Slovak University of Technology, Ilkovičova 3, 812 19 Bratislava, SlovakiabJRC Petten, European Commission, Postbus 3, 1755 PG PettencLRT2, Universität der Bundeswehr München, Werner-Heisenberg-Weg 39, D-85577 Neubiberg, GermanydInstitute of Materials Science, Slovak University of Technology, Bottova 25, 917 24 Trnava, Slovakiaemail: stanislav.sojak@stuba.sk

  2. Outline • Motivation • Positron annihilation spectroscopy • Experimental Fe-Cr results • Binary Fe-Cr alloys treatments • Results of annealed Fe-11.62%Cr alloys • Summary 2

  3. Motivation • Investigation of Reduced Activation Ferritic/Martensitic (RAFM) steels as a candidate structural materials for new fission/fusion reactors. • Radiation damage simulation by ion implantation. • Different temperatures annealing of the steels in order to study changes in microstructure • Positron lifetime measurements before and after treatment and evaluation of measured results. 3

  4. Pulsed low energy positron system(PLEPS) remoderated positrons [1] P. Sperr, W. Egger, G. Kögel, G. Dollinger, Ch. Hugenschmidt, R. Repper, C. Piochacz, Applied Surface Science 255 (2008) 35–38 [2] Hugenschmidt C., Dollinger G., Egger W., Kögel G.,Löwe B., Mayer J., Pikart P., Piochacz C., Repper R., Schreckenbach K., Sperr P., Stadlbauer M., Applied Surface Science, Volume 255, Issue 1, p. 29-32 4

  5. Spectra evaluation • Measured spectra evaluation by PosWin software. • Output – positron lifetimes (3 components): • τ1: positron lifetime in bulk • τ2: positron lifetime in defects • τ3: positron lifetime in large defects • Intensity of each component (I1, I2, I3) • Mean lifetime (MLT) 5

  6. Experiment & Results

  7. Specimens preparation: Dimensions 10x10x0,4 mm, One side mirror-like polished Binary Fe-Cr alloys treatment Manufactured at Dept. of Metallurgy at Ghent University, Belgium 7

  8. Radiation damage simulation • Simulation of radiation damage of binary Fe-Cr alloys by ion implantation • Implantation of He ions with energy of 250 & 100 keV • Dose of implanted ions: 0.1 – 0.5 C/cm2 (6.24x1017 – 3.12x1018 ions/cm2) 8

  9. Thermal annealing • Influence of thermal annealing of structural changes. • Annealed:Fe-11.62%Cr: 0; 0.1; 0.3; 0.5 C/cm2. • Annealing temperatures400, 475, 525, 600 ºCfor 2 hours • Argon atmosphere, pressure 10 kPa 9

  10. 1mm Z x Scanning electron microscopy (SEM) results of not annealed Fe-Cr alloy SEM results show the PLEPS prediction of large voids in the depth >500nm, which correspond to the helium implantation profile maximum. [3] KRŠJAK, V.: Positron annihilation study of advanced nuclear reactor materials, Doctoral thesis, Slovak University of Technology, Slovakia, 2008. 10

  11. SRIM simulations • Depth profile of binary Fe-Cr alloy after 250 & 100 keV He2+ ion implantation. 11

  12. PLEPS results of Fe-11.62%Cr • No peaks from 100 and 250 keV Helium ions were observed. • Therefore other technique support was needed. 12

  13. Diagonal cut under the 12º angle of the Fe-11.62%Cr specimen, 1 μm annealed at 475 ºC. Major damage in two regions, considering the SRIM simulation => damaged areas from 100 and 250 keV Helium ~0.3 μm ~0.55 μm ~1 μm 13

  14. At 600 ºC was observed significant decrease of meanpositron lifetime. It should mean annealing out of defects size/amount. How the structure looks like under SEM at this temperature? MLT after 600 °C [4] RONALD, K.L. – HARRIES, D.R.: High-Chromium Ferritic and Martensitic steels for Nuclear Applications, ASTM USA (2001). 14

  15. Positron lifetimes in defects and bulks (τ2, τ1) • >200 nm oxide layer is influencing defects and bulk lifetimes. • Defects lifetime of specimens annealed at 600 °C decreased also in comparison to not annealed specimen. Intensity stays increasing with depth. • Positron lifetime in bulk reached level of 140 ps, which corresponds to bulk with dislocations [3]. 15

  16. Summary • Significant damage areas were observed by SEM technique in Fe-11.62%Cr alloy annealed at 475 ºC but no peaks from PLEPS technique were registered. • Extensive decrease of positron lifetimes in case of 600 ºC annealed specimens was observed. The bulk was well recognized with high intensity level. • Questions about the structure changes at temperature of 600 ºC is still going to front rank and more experiments with SEM has to be done. • Ion implantation damage with connection to the thermal annealing at lower temperatures and oxide layer on the surface introduced many variables and created complicated system for the final evaluation of measured data. Because of such significantly damaged structure, we will use for next experiments lower implantation energies to maximum level of 0.3 C/cm2.

  17. Thank you for your attention!

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