Positron and Positronium Chemistry PPC10, September, Smolenice Castle, Slovakia Thermal annealing influence on ions implanted Fe-Cr model alloys S. Sojak a,, V. Slugeň a, V. Kršjak b, W. Egger c, L. Ravelli c, M. Petriska a, S. Stanček a, M. Skarba d, P. Priputen d, K. Vitázek a, M. Stacho a, J. Veterníková a, V. Sabelová a a Institute of Nuclear and Physical Engineering, Slovak University of Technology, Ilkovičova 3, Bratislava, Slovakia b JRC Petten, European Commission, Postbus 3, 1755 PG Petten c LRT2, Universität der Bundeswehr München, Werner-Heisenberg-Weg 39, D Neubiberg, Germany d Institute of Materials Science, Slovak University of Technology, Bottova 25, Trnava, Slovakia

Positron and Positronium Chemistry PPC10, September, Smolenice Castle, Slovakia Outline Motivation Positron annihilation spectroscopy Experimental Fe-Cr results Binary Fe-Cr alloys treatments Results of annealed Fe-11.62%Cr alloys Summary 2

Positron and Positronium Chemistry PPC10, September, Smolenice Castle, Slovakia 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

Positron and Positronium Chemistry PPC10, September, Smolenice Castle, Slovakia 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

Positron and Positronium Chemistry PPC10, September, Smolenice Castle, Slovakia Spectra evaluation Measured spectra evaluation by PosWin software. Output – positron lifetimes (3 components):  τ 1 : positron lifetime in bulk  τ 2 : positron lifetime in defects  τ 3 : positron lifetime in large defects  Intensity of each component (I 1, I 2, I 3 )  Mean lifetime (MLT) 5

Positron and Positronium Chemistry PPC10, September, Smolenice Castle, Slovakia Experiment & Results

Positron and Positronium Chemistry PPC10, September, Smolenice Castle, Slovakia Binary Fe-Cr alloys treatment Specimen Cr [wt%] P [wt%] Si [wt%] Al [wt%] Ti [wt%] Mn [wt%] Ni [wt%] Cu [wt%] C [wt%] N [wt%] V [wt%] L L L L Specimens preparation: Dimensions 10x10x0,4 mm, One side mirror-like polished Manufactured at Dept. of Metallurgy at Ghent University, Belgium 7

Positron and Positronium Chemistry PPC10, September, Smolenice Castle, Slovakia 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/cm 2 (6.24x10 17 – 3.12x10 18 ions/cm 2 ) 8

Positron and Positronium Chemistry PPC10, September, Smolenice Castle, Slovakia Influence of thermal annealing of structural changes. Annealed: Fe-11.62%Cr: 0; 0.1; 0.3; 0.5 C/cm 2. Annealing temperatures 400, 475, 525, 600 ºC for 2 hours Argon atmosphere, pressure 10 kPa Thermal annealing 9

Positron and Positronium Chemistry PPC10, September, Smolenice Castle, Slovakia [3] KRŠJAK, V.: Positron annihilation study of advanced nuclear reactor materials, Doctoral thesis, Slovak University of Technology, Slovakia, Scanning electron microscopy (SEM) results of not annealed Fe-Cr alloy 10 x Z 1m1m SEM results show the PLEPS prediction of large voids in the depth >500nm, which correspond to the helium implantation profile maximum.

Positron and Positronium Chemistry PPC10, September, Smolenice Castle, Slovakia SRIM simulations Dose [ions/cm 2 ]6.24x x x x x10 18 DPA Depth profile of binary Fe-Cr alloy after 250 & 100 keV He 2 + ion implantation. 11

Positron and Positronium Chemistry PPC10, September, Smolenice Castle, Slovakia 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

Positron and Positronium Chemistry PPC10, September, Smolenice Castle, Slovakia 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 13 ~1 μm ~0.3 μm ~0.55 μm

Positron and Positronium Chemistry PPC10, September, Smolenice Castle, Slovakia MLT after 600 °C At 600 ºC was observed significant decrease of mean positron lifetime. It should mean annealing out of defects size/amount. How the structure looks like under SEM at this temperature? 14 [4] RONALD, K.L. – HARRIES, D.R.: High-Chromium Ferritic and Martensitic steels for Nuclear Applications, ASTM USA (2001).

Positron and Positronium Chemistry PPC10, September, Smolenice Castle, Slovakia Positron lifetimes in defects and bulks (τ 2, τ 1 ) >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

Positron and Positronium Chemistry PPC10, September, Smolenice Castle, Slovakia Summary Significant damage areas were observed by SEM technique in Fe %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/cm 2.

Positron and Positronium Chemistry PPC10, September, Smolenice Castle, Slovakia Thank you for your attention!