Positron and Positronium Chemistry PPC10, 2. -5. September, Smolenice Castle, Slovakia Thermal annealing influence on ions implanted Fe-Cr model alloys

Positron and Positronium Chemistry PPC10, 2. -5. September, Smolenice Castle, Slovakia

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

aInstitute of Nuclear and Physical Engineering, Slovak University of Technology, Ilkovičova 3, 812 19 Bratislava, Slovakia

bJRC 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, Slovakia

email: [email protected]


Outline

Motivation

Positron annihilation spectroscopy

Experimental Fe-Cr results Binary Fe-Cr alloys treatments

Results of annealed Fe-11.62%Cr alloys

Summary

2


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


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


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)

332211 ... IIIMLT

1 iI

5


Experiment & Results


Binary Fe-Cr alloys treatmentSpecimen Cr

[wt%]

P[wt%]

Si[wt%]

Al[wt%]

Ti[wt%]

Mn [wt%]

Ni[wt%]

Cu[wt%]

C[wt%]

N[wt%]

V[wt%]

L251 2.36 0.013 0.002 0.003 0.004 0.009 0.044 0.005 0.008 0.0173 0.001

L259 4.62 0.011 0.006 0.0033 0.0028 0.02 0.06 0.01 0.02 0.0344 0.001

L252 8.39 0.012 0.00066 0.0069 0.0034 0.03 0.07 0.01 0.02 0.0353 0.002

L253 11.62 0.05 0.006 0.003 0.0037 0.03 0.09 0.01 0.03 0.0397 0.002

Specimens preparation:

Dimensions 10x10x0,4 mm,

One side mirror-like polished

Manufactured at Dept. of Metallurgy at Ghent University, Belgium

7


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


Influence of thermal annealing of structural changes.

Annealed: Fe-11.62%Cr: 0; 0.1; 0.3; 0.5 C/cm2.

Annealing temperatures 400, 475, 525, 600 ºC for 2 hours

Argon atmosphere, pressure 10 kPa

Thermal annealing

9


[3] KRŠJAK, V.: Positron annihilation study of advanced nuclear reactor materials, Doctoral thesis, Slovak

University of Technology, Slovakia, 2008.

Scanning electron microscopy (SEM) results of not annealed Fe-Cr alloy

10

xZ

1m

SEM results show the PLEPS prediction of large voids in the depth >500nm, which correspond to the helium implantation profile maximum.


SRIM simulations

Dose [ions/cm2] 6.24x1017 1.24x1018 1.87x1018 2.5x1018 3.12x1018

DPA 18.51 37.02 55.53 74.05 92.56

Depth profile of binary Fe-Cr alloy after 250 & 100 keV He2

+ ion implantation.

11


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

0 2 4 6 8 10 12 14 16 18 20

160

180

200

220

240

260

280

300

320

340

360

380

400

420

not annealed 400 C 475 C 525 C

523433273 35020490 14347

Fe-11.62%Cr: irr. 0.3 C/cm2

Mean p

ositron life

time [p

s]

Positron energy [keV]

16

Depth [nm]


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


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

0 2 4 6 8 10 12 14 16 18 20

160

180

200

220

240

260

280

300

320

340

360

380

400

420

not annealed 400 C 475 C 525 C 600 C

523433273 35020490 14347

Fe-11.62%Cr: irr. 0.3 C/cm2

Mean p

ositron life

time [p

s]


16

Depth [nm]

[4] RONALD, K.L. – HARRIES, D.R.: High-Chromium Ferritic and Martensitic steels for Nuclear Applications, ASTM USA (2001).


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].

0 2 4 6 8 10 12 14 16 18 20220

240

260

280

300

320

340

360

380

400

420

440

460

480

500

not annelaed 400 C 475 C 525 C 600 C

523433273 35020490 14347

Fe-11.62%Cr: irr. 0.3 C/cm2

Positron life

time in

defe

cts

[ps]


16

Depth [nm]

0 2 4 6 8 10 12 14 16 18 200

20

40

60

80

100

120 not annealed 400 C 475 C 525 C 600 C

523433273 35020490 14347

Fe-11.62%Cr: irr. 0.3 C/cm2

Inte

nsity

I 2 [%

]


16

Depth [nm]

0 2 4 6 8 10 12 14 16 18 20

020406080

100120140160180200220240260280300320340360380400


523433273 35020490 14347

Fe-11.62%Cr: irr. 0.3 C/cm2

Pos

itron

life

time

1 [p

s]


16

Depth [nm]

0 2 4 6 8 10 12 14 16 18 20

0

20

40

60

80

100

120


523433273 35020490 14347

Fe-11.62%Cr: irr. 0.3 C/cm2

Inte

nsity

I 1 [%

]Positron energy [keV]

16

Depth [nm]

15


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.


Thank you for your attention!

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Positron and Positronium Chemistry PPC10, 2. -5. September, Smolenice Castle, Slovakia Thermal annealing influence on ions implanted Fe-Cr model alloys