Atom Probe Tomography of Ion-Irradiated Model ODS Alloys

Andrew London* 4th Year DPhilC.R.M Grovenor, S Lozano-Perez*

B. K. Panigrahi**

* Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, UK** Indira Gandhi Centre for Atomic Research, Kalpakkam - 603 102, TN, India

Y, YO blueTi, TiO greenO, FeO red

Purpose of my research

What questions are we trying to answer?• Oxide dispersion strengthened steel:

– What are the dispersed oxides, structure/chemistry? So we can control them and therefore the materials’ properties.

– What is the influence of alloy chemistry on oxide particles, specifically chromium?

– What is the influence of ion-irradiation?

Purpose of my research

What questions are we trying to answer?• Oxide dispersion strengthened steel:

– What are the dispersed oxides, structure/chemistry? So we can control them and therefore the materials’ properties.

– What is the influence of alloy chemistry on oxide particles, specifically chromium?

– What is the influence of ion-irradiation?

London, A. J., et al. "Comparison of atom probe tomography and transmission electron microscopy analysis of oxide dispersion strengthened steels." Journal of Physics: Conference Series. Vol. 522. No. 1. IOP Publishing, 2014.

Purpose of my research

What questions are we trying to answer?• Oxide dispersion strengthened steel:

– What are the dispersed oxides, structure/chemistry? So we can control them and therefore the materials’ properties.

– What is the influence of alloy chemistry on oxide particles, specifically chromium?

– What is the influence of ion-irradiation?

Expectation: High temperatureAs-received

500 C 75 dpa

500 C 150 dpa

Lescoat, M-L., et al. Acta Materialia 78 (2014): 328-340.

Allen, Todd R., et al. Journal of Nuclear Materials 375.1 (2008): 26-37.

He, Jianchao, et al. Journal of Nuclear Materials 455.1 (2014): 41-45.

Expectation: Low temperatureRoom temperature

Lescoat, M-L., et al. Acta Materialia 78 (2014): 328-340.

“the 100 dpa, −75 °C samples data set showed no significant clustering … Y, Ti, and O were randomly distributed in solid solution.”

Certain, A., et al. Journal of Nuclear Materials 434.1 (2013): 311-321.

(own work) Irrd. at 120K (a), and as-received (b)

Indian Programme on ODS Materials• Currently working on a ODS cladding tube alloy.• Fe-9Cr-2W-0.1C-0.2Ti-0.35Y2O3

Clad-tubes with 6.6 mm O.D., 0.45 mm thick and 4.2 m length have been successfully produced

Pre-alloyed powder

Nanocrystalline yttria

My Collaboration with Indira Gandhi Centre for Atomic Research (IGCAR)

Three model alloys produced by extrusion to study the influence of alloy content.

Nominal Compositions: (wt %)• Fe–14Cr–0.2Ti–0.3Y2O3

• Fe–0.2Ti–0.3Y2O3

• Fe–0.3Y2O3

Methods:Example TEM and APT of the same sample

100 nm

Large Yttrium & Oxygen particle Carbon on grain boundary

Atom Probe data

Y & YO

Ti & TiO

Oxygen

Low-temperature irradiation

As-receivedFe-14Cr-0.2Ti-0.3Y2O3

50 nm

>50 dpa @ 120K

Y/YO TiO/Ti

surface

Low-temperature irradiation

20 n

m

100 nm

50 nm

Cr-oxide contamination particle

150K Ion Irradiation of Fe-Ti-Y2O3 ODS alloysto 100 dpa

CarbideMatrix

diffuse Y-Ti clusters

0 20 40 60 800

5

10

15

Distance nm

Ca

rbo

n %

CarbonErf fit

50 nm

High-temperature irradiationAs-receivedFe-14Cr-0.2Ti-0.3Y2O3

>50 dpa @ 900KIncreased Ti content of the clusters, but no significant change to number density or size distribution

High-temperature irradiation

The high-yttrium content clusters are lost, more Ti-rich oxides are observed and the average Ti-fraction of the clusters increases.

Fe14Cr-0.2Ti-0.3Y2O3 ~50 dpa, APT data

High-temperature irradiation

No significant change in radius, but reduction in average number density with irradiation at 500 to 600 C.

Fe14Cr-0.2Ti-0.3Y2O3 ~50 dpa, APT data

After cryo-irradiation:

50 nm

Annealed @ 900K

Irradiated @ 900K100 dpa0 dpa

50 nm

Irradiated @ 900K(after 120K irradiation)

50 nm

grain boundaries

High number density of small “flat” clusters

Monnet et al. JNM 335.3 (2004): 311-321.800K, 78.8 dpa, 25 days

10 nm

Preliminary conclusions• Irradiation at low temperature does not homogenise the

solute distribution as reported by others [1,2], but does partially dissolve the particles.

• Subsequent annealing results in similar particles to the original, even at “low” temperatures (900K).

• Subsequent ion-irradiation at high temperature forms a high number density of very small clusters, with a high solute concentration on the grain boundaries.

• It is possible to use ion irradiation as an analogue for neutron damage but care is required to design appropriate experiments.

[1] Certain, A., et al. Journal of Nuclear Materials 434.1 (2013): 311-321.[2] Parish, CM., et al. Journal of Nuclear Materials 445.1 (2014): 251-260.

Any Questions?