Thermal annealing influence on ions implanted FeCr model

Thermal annealing influence on ions implanted Fe-Cr model alloys S. Sojaka, , V. Slugeňa, V. Kršjakb, W. Eggerc, L. Ravellic, M. Petriskaa, S. Stančeka, M. Skarbad, P. Priputend, K. Vitázeka, M. Stachoa, J. Veterníkováa, V. Sabelováa a. Institute of Nuclear and Physical Engineering, Slovak University of Technology, Ilkovičova 3, 812 19 Bratislava, Slovakia b. JRC Petten, European Commission, Postbus 3, 1755 PG Petten c. LRT 2, Universität der Bundeswehr München, Werner-Heisenberg-Weg 39, D-85577 Neubiberg, Germany d. Institute of Materials Science, Slovak University of Technology, Bottova 25, 917 24 Trnava, Slovakia email: stanislav. sojak@stuba. sk Positron and Positronium Chemistry PPC 10, 2. -5. September, Smolenice Castle, Slovakia

Outline n Motivation n Positron annihilation spectroscopy n Experimental Fe-Cr results n n Binary Fe-Cr alloys treatments n Results of annealed Fe-11. 62%Cr alloys Summary Positron and Positronium Chemistry PPC 10, 2. -5. September, Smolenice Castle, Slovakia 2

Motivation n Investigation of Reduced Activation Ferritic/Martensitic (RAFM) steels as a candidate structural materials for new fission/fusion reactors. n Radiation damage simulation by ion implantation. n Different temperatures annealing of the steels in order to study changes in microstructure n Positron lifetime measurements before and after treatment and evaluation of measured results. Positron and Positronium Chemistry PPC 10, 2. -5. September, Smolenice Castle, Slovakia 3

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 Positron and Positronium Chemistry PPC 10, 2. -5. September, Smolenice Castle, Slovakia

Spectra evaluation n n Measured spectra evaluation by Pos. Win software. Output – positron lifetimes (3 components): q τ1: positron lifetime in bulk q τ2: positron lifetime in defects q τ3: positron lifetime in large defects q Intensity of each component (I 1, I 2, I 3) q Mean lifetime (MLT) 5 Positron and Positronium Chemistry PPC 10, 2. -5. September, Smolenice Castle, Slovakia

Experiment & Results Positron and Positronium Chemistry PPC 10, 2. -5. September, Smolenice Castle, Slovakia

Binary Fe-Cr alloys treatment Specimen P Si Al Ti Mn Ni Cu C N V [wt%] [wt%] [wt%] L 251 2. 36 0. 013 0. 002 0. 003 0. 004 0. 009 0. 044 0. 005 0. 008 0. 0173 0. 001 L 259 4. 62 0. 011 0. 006 0. 0033 0. 0028 0. 02 0. 06 0. 01 0. 02 0. 0344 0. 001 L 252 8. 39 0. 012 0. 00066 0. 0069 0. 0034 0. 03 0. 07 0. 01 0. 02 0. 0353 0. 002 L 253 11. 62 0. 05 0. 006 0. 0037 0. 03 0. 09 0. 01 0. 0397 0. 002 Cr Manufactured at Dept. of Metallurgy at Ghent University, Belgium Specimens preparation: Dimensions 10 x 0, 4 mm, One side mirror-like polished Positron and Positronium Chemistry PPC 10, 2. -5. September, Smolenice Castle, Slovakia 7

Radiation damage simulation n Simulation of radiation damage of binary Fe-Cr alloys by ion implantation Implantation of He ions with energy of 250 & 100 ke. V Dose of implanted ions: 0. 1 – 0. 5 C/cm 2 (6. 24 x 1017 – 3. 12 x 1018 ions/cm 2) Positron and Positronium Chemistry PPC 10, 2. -5. September, Smolenice Castle, Slovakia 8

Thermal annealing n n 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 k. Pa Positron and Positronium Chemistry PPC 10, 2. -5. September, Smolenice Castle, Slovakia 9

Scanning electron microscopy (SEM) results of not annealed Fe-Cr alloy SEM results show the PLEPS prediction of large voids in the depth >500 nm, which correspond to the helium implantation profile maximum. 1 m m Z x [3] KRŠJAK, V. : Positron annihilation study of advanced nuclear reactor materials, Doctoral thesis, Slovak University of Technology, Slovakia, 2008. Positron and Positronium Chemistry PPC 10, 2. -5. September, Smolenice Castle, Slovakia 10

SRIM simulations n Depth profile of binary Fe-Cr alloy after 250 & 100 ke. V He 2+ ion implantation. Dose [ions/cm 2] 6. 24 x 1017 1. 24 x 1018 1. 87 x 1018 2. 5 x 1018 3. 12 x 1018 DPA 18. 51 37. 02 55. 53 74. 05 92. 56 Positron and Positronium Chemistry PPC 10, 2. -5. September, Smolenice Castle, Slovakia 11

PLEPS results of Fe-11. 62%Cr n n No peaks from 100 and 250 ke. V Helium ions were observed. Therefore other technique support was needed. Positron and Positronium Chemistry PPC 10, 2. -5. September, Smolenice Castle, Slovakia 12

~0. 3 μm ~0. 55 μm ~1 μm n n 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 ke. V Helium Positron and Positronium Chemistry PPC 10, 2. -5. September, Smolenice Castle, Slovakia 13

MLT after 600 °C n n At 600 ºC was observedsignificant decrease of mean positron lifetime. It should mean annealing out of defects size/amount. How the structure looks like under SEM at this temperature? [4] RONALD, K. L. – HARRIES, D. R. : High-Chromium Ferritic and Martensitic steels for Nuclear Applications, ASTM USA (2001). Positron and Positronium Chemistry PPC 10, 2. -5. September, Smolenice Castle, Slovakia 14

Positron lifetimes in defects and bulks (τ2, τ 1) n n n >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]. Positron and Positronium Chemistry PPC 10, 2. -5. September, Smolenice Castle, Slovakia 15

Summary n 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. n Extensive decrease of positron lifetimes in case of 600 ºC annealed specimens was observed. The bulk was well recognized with high intensity level. n 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. n Ion implantation damage with connection to 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 PPC 10, 2. -5. September, Smolenice Castle, Slovakia

Thank you for your attention! Positron and Positronium Chemistry PPC 10, 2. -5. September, Smolenice Castle, Slovakia