interfaces: corrosion in pb-alloy cooled nuclear reactors ... documents/workshop...

KIT – Universität des Landes Baden-Württemberg und

nationales Forschungszentrum in der Helmholtz-Gemeinschaft www.kit.edu

Interfaces:

Corrosion in Pb-alloy cooled nuclear reactors and

advanced mitigation measures

A. Weisenburger and G. Müller– KIT

M. Del Giacco , A. Weisenburger , G. Müller – IHM/KIT 2

Challenges for coolants in fast spectrum system: Chemistry and materials Vienna July 5th – 7th A. Weisenburger

Solubility of elements in Pb/PbBi Dissolution attack - corrosion

Steel corrosion in liquid Pb-alloys

1.4970 steel exposed to LBE at 600°C

Way Out: insoluble materials (W, Mo, ..,

ceramics)

or

like e.g. in atmospheric conditions – protection

by oxide scales growing in the media



Ellingham diagram


Way out:

Oxide scale on the steel surface

prevent the dissolution

liquid metal steel steel

T1

aXT1

T2

aXT

2

T1 > T2

aXT1 > aLM > aXT2

oxide scale oxide scale

diffusion barrier for Cations!

f/m steel at 550°C in LBE

At present only

austenitic steels

are considered

in contact with

liquid Pb-alloys

due to LME of

f/m steels



Oxygen content vs temperature


Pb

LBE

420°C / 4000 h 30µm

Austenitic steels can be used up to 450°C

Oxygen content >10-7wt% required

Higher T or lower oxygen content

Advanced mitigation measures

OECD Liquid metal handbook (2015)




Data from flowing LBE 2m/s

Incubation time for corrosion attack

Localized corrosion is one of the main

concerns - origin still unknown

Austenitic steels can be used up to 450°C ?

Oxygen content >10-7wt% required ?

Higher T or lower oxygen content





Some general requirements for advanced mitigation measures

Corrosion resistant in HLM between 400°C and 650 °C

No delamination of the coating during operation or handling - coatings

Self healing of mechanically damaged layers - surface alloys / bulk

In-situ Formation

Reservoir layer

No negative influence on mechanical properties

Irradiation stability under relevant fluxes

The coating/alloying process should be of industrial relevance

• (1) Insoluble ceramic coatings – TiN, AlTiN, Al2O3, …..

• (2) Formation of Alumina scale during operation

• Al- containing surface alloys – FeCrAl

• Alumina forming steels – FeCrAl, AFA

• Alumina forming HEA

• (3) MAXPHASES



Insoluble ceramic coatings – TiN, AlTiN, Al2O3

PLD of Al2O3 scales on cladding tubes (IIT, Italy)

γ-Al2O3

steel

†† †

†

• post-annealing (600°C,Ar) ≈ 10 nm γ-Al2O3

• fully dense and compact microstructure • Some droplet ejection

500 μm

• 1% vol. γ-Al2O3 randomly oriented crystalline Al2O3 nanodomains in an amorphous Al2O3 matrix

Al2O3

substrate 500 nm

F. García Ferré et al. – Corros.Sci. 2017

Exposure tests showed excellent corrosion resistance

1st thermal cycling tests (600-350°C 25X) no delamination no cracks

Ceramic hardness combined with almost metallic E-Module

Ion irradiation exhibit excellent irradiation stability

Scalability ?, No self-healing in service inspection, maintenance ??



In-service formation of Alumina as protective coating

Al2O3

Al2O3 layer

Fe(Cr,Al)-phase

Steel

Al2O3 is very stable oxide

Diffusion in Al2O3 very low

slowly growing

perfect barrier

No interaction with Pb-alloys

No coating: either surface alloy or bulk

Reservoir layer – self healing

Proven at other high temperature applications

Oxide map of FeCrAl - oxide

at 900 °C in gas

• Al- containing surface alloys – FeCrAl

• Alumina forming steels – FeCrAl, AFA

• Alumina forming HEA



Al - containing coatings – Surface alloys

Magnetic

coils

anode

target

GESA

Electron beam parameter:

electron energy: 50 - 140 keV

energy density : ~ 2 MW/ cm²

pulse duration controllable: 1 -

200µs

Beam diameter: 5 - 10 cm

The procedure consists in two steps:

(i) pre-coating the surface steel with Al-containing alloy (Fe-Cr-Al system)

(ii) (ii) melting the coating and the surface layer of the steel using intense

pulsed electron beams (GESA process – Karlsruhe Institute of Technology).

LPPS – E-beam -others

GESA treatment leads to:

metallic bonding – pore removal – surface smoothening and reduced Al content



Pb/PbBi compatibility of Al surface alloyed steel

at optimal oxygen concentration 10-6 wt%

10000 h 10000 h

500°C 600°C 550°C

Up to 600°C and 10000 h no

corrosion attack and no visible

oxidation. Fe12Cr7Al

Thin alumina scales protect the

surface alloyed steel.

20µm 20µm

Specimen at 550°C Al< 4wt%

„normal Fe-based scales

?optimum Al/Cr content?

Bulk FeCrAl to answer this

question



Reactive elements influence on the corrosion behavior

(400-600°C) Exposure tests in Pb

Fe-16Cr-4Al-0.5Zr Fe-16Cr-4Al-0.5Hf

Alumina forming steels - Bulk FeCrAl +RE

FeCrAl + RE manufactured and exposed to Pb alloy

Fe-16Cr-8Al-0.5Y; Fe-16Cr-6Al-0.5Y

Fe-16Cr-8Al-0.5Zr; Fe-16Cr-6Al-0.5Zr; Fe-16Cr-4Al-0.5Zr

Fe-16Cr-8Al-0.5Hf; Fe-16Cr-6Al-0.5Hf; Fe-16Cr-4Al-0.5Hf

Fe-16Cr-8Al-0.25Hf-0.25Zr; Fe-16Cr-6Al-0.25Hf-0.25Zr; Fe-16Cr-

4Al-0.25Hf-0.25Zr

Fe-16Cr-8Al-0.5Mo; Fe-16Cr-6Al-0.5Mo; Fe-16Cr-4Al-0.5Mo



Protective oxides, balanced Zr/C (no

surface carbides)

TEM BF micrographs showing the alumina layer formed on Zr-0.2 at a. 450°C (1,000 h)

and b. 550 °C (8,760 h).

450°

550°C

Oxygen~10-7wt%



Al2O3 formation at entire temperature range requires a certain Al, Cr ratio

Reactive elements like Y, Zr, Hf foster the alumina formation

Both Surface alloyed and bulk FeCrAl can protect the steels in Pb up to 750°C

Oxide map of FeCrAl+RE in Pb-alloys

between 450 and 600°C – oxygen 10-6wt%



Metal powder Arc melter heat treatment (rapid cooling/quarz glas capsule)

1250°C 2h – rapid cooling in water

exposure in Pb at 600°C – preliminary investigation

Alumina forming steels – AFA at KIT

Fe Cr Ni Nb Al Ti Mn Zr

D29 45 14 32 3 3 2 0,2 0,32

41Z 46 14 32 4 3 1 0,27

8 different alloys: 10 Cr , Al (2-4), Ni (16-30) - dissolution attack

Minimum Cr content required

Alumina scales in Pb



Next steps with AFA- alloys selected and produced

Based on 1st results - start with simple model alloys

to evaluate minimum Al and Cr content required, maximum Ni content allowed –

Phases are measured after heat treament

Code Al(wt.%) Cr (wt.%) Ni (wt.%) Fe (wt.%) Phases Sh44 3 14 20 63 FCC

Sh45 2.5 16 20 61.5 FCC

Sh46 3 16 20 61 FCC

Sh47 3 16 22 59 FCC

Sh48 4 12 22 62 FCC

Sh49 4 14 22 60 FCC

Sh50 2.5 16 22 59.5 FCC

Sh51 4 12 24 60 FCC

Sh52 4 14 24 58 FCC

Sh53 3 16 24 57 FCC

Sh54 4 16 24 56 FCC

Sh55 2.5 15 29 53.5 FCC Sh56 3.5 15 29 52.5 FCC

These AFA alloys are actually exposed to Pb at 600°C for 2000h

Based on corrosion resistant small punch test to evaluate brittleness

Additional elements to optimize mechanical properties



Alumina forming HEA -5 alloys AlCrFeNiX (X: Co Mn)

Al11.1Cr22.2Fe22.2Ni22.3Mn22.2

Al12.7Cr21.6Fe21.8Ni21.6Co21.6Y0.7

HEA new class of materials

Excellent mechanical properties also at high

temperatures

Indications to be stable under irradiation

Adding Al – compatible with Pb-alloys

Corrosion resistance proved

Mechanical and irradiation tests pending



450 475 500 525 5500,00

0,05

0,10

0,15

0,20

Fre

ttin

g d

ep

th [

mm

]

Temperature [°C]

T91

15-15Ti

GESA-T91

0,0

0,1

0,2

0,3

0,4

Fre

ttti

ng

de

pth

/ F

ue

l cl

ad

th

ickn

ess

Fig. 4b: fretting damage as function of temperatureure

Secondary creep rate in LBE and Air-

threshold stress fretting damage as function of temperature

In-situ formed Alumina-scales can mitigate influence of combined loads

Surface alloyed f/m steels? Alumina forming f/m steels an option again?

Alumina forming surface allyos under combined load



Summary Outlook

EERA-JPNM PP – ALCORE – focus on Alumina forming

- STAR-TREC focus on Al2O3 coating

- CERBERUS – focus on corrosion

all these PP are partially funded in the H2020 project GEMMA

Corrosion is an issue for Pb-alloys foreseen as coolants

f/m steels are not considered at present – LME

Austenitic steels (Ni-solubility) limit at ~450°C, but even there

localized corrosion attack

Open question regarding compatibility:

What are the „real“ limits of existing materials in Pb-alloys

regarding temperature, oxygen content, flow rate, mechanical load?

There are advanced mitigation strategies available > 600°C feasible

Coatings

Surface alloys and bulk alumina formers

None of these is yet fully characterized

None of these is ready now – coatings and surface alloys more advanced

All require more R&D

interfaces: corrosion in pb-alloy cooled nuclear reactors ... documents/workshop...

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