fundamental understanding of nb effect on corrosion … · 2019-06-26 · • shape of the nb...

Fundamental understanding of Nb

effect on corrosion mechanisms of

Zr-Nb alloys in and out of reactor

Zefeng Yu1, Michael Moorehead2, Leo Borrel2,

Mukesh Bachhav3, Lingfeng He3, Jing Hu4 and Adrien Couet1,2

1University of Wisconsin, Madison – Material Science and Engineering Department2University of Wisconsin, Madison – Engineering Physics Department

3Idaho National Laboratory – Materials and Fuels Complex4Argonne National Laboratory – Intermediate Voltage Electron Microscopy-Tandem Facility

UW Environmental Degradation of Nuclear Materials Laboratory

19th International Symposium on Zirconium in the Nuclear Industry

2

RESEARCH BACKGROUND AND MOTIVATION

• Irradiation effect on microstructure of ZrNb alloy:

• In-reactor irradiation induces “βNb” platelets [2].

• Proton irradiation also induces the precipitation of those platelets [3].

• Hypothesis: Irradiation reduces Nb concentration in α-Zr matrix by

precipitating Nb-rich irradiation-induced platelets resulting in lower

corrosion kinetics

[2] Doriot, S, et al. ASTM Special Technical Publication, vol. 1543, 2015, pp. 759–799.

1 dpa proton irradiated M5 neutron irradiated M5

[3] Verlet, Romain. Influence of Irradiation and Radiolysis on the Corrosion Rate and Mechanisms of Zirconium Alloys, 2015.



14 dpa

3

720 Cͦ

580 Cͦ

ZrNb Microchemistry Effect on Corrosion Kinetics:

• Understand how Nb distribution affect corrosion kinetics of Zr alloys.

Samples:

• 720 Cͦ Zr-1.0Nb: αZr + βZr (Fe = 750 ppm)

• 580 Cͦ Zr-1.0Nb: αZr + βNb + Laves phases (Fe = 600 ppm)



720 ͦC 580 ͦC

Expected microstructures:

UNIRRADIATED ZR-1.0NB MODEL ALLOY

1. Nb distribution and electronic structure in the oxide

4UW Environmental Degradation of Nuclear Materials Laboratory


CORROSION KINETICS OF ZR-1.0NB


1. Exponent of oxidation kinetics

varies from:

0.5 (720°C) → 0.36 (580°C)

2. Parabolic kinetics are

typically associated with

electroneutrality (and other

things…)

3. Sub-parabolic kinetics can

be caused by space charges

(and other things…)

5

UNIRRADIATED ZR-1.0NB CHARACTERIZATION• 720 Cͦ Zr-1.0Nb:

αZr + βZr (highlighted in yellow)

βZr



• 580 Cͦ Zr-1.0Nb:

aZr + βNb (highlighted in red)

BF HAADF


[5] M. Moorehead, Z. Yu, L. Borrel, Z. Couet, J. Hu, Z. Cai, Comprehensive Investigation of the

Role of Nb on the Oxidation Kinetics of Zr-Nb Alloys, Corrosion Science (2019).

After corrosion

360 °C, 18 MPa

Nb in βZr

dissolves in oxide

βNb remains in

oxide, limited Nb

dissolution

7 daysThickness:

0.86 μm

45 daysThickness:

1.8 μm

6

UNIRRADIATED ZR-1.0NB CHARACTERIZATION

• Microchemistry of βZr at oxide and metal interface :




[5] M. Moorehead, Z. Yu, L. Borrel, Z. Couet, J. Hu, Z. Cai, Comprehensive Investigation of the

Role of Nb on the Oxidation Kinetics of Zr-Nb Alloys, Corrosion Science (2019).

oxi

de

metal

• Nb is seen to leech out from the β-Zr precipitate upon oxidation.

• Doping the oxide with additional Nb in solid solution

• WHAT IS THE Nb OXIDATION STATE?

Incident X-Ray Energy

Monochromatic

X-Ray Beam

X-Ray Detector

Nb Kα X-Ray

• Monochromatic incident X-ray beam is

increased in energy

• Shape of the Nb Kα X-ray emission

curve can be fit to known standards

using Athena

• Metallic/Oxidized fractions can then

be determined 0

0.2

0.4

0.6

0.8

1

1.2

1.4

18950 19000 19050 19100

No

rmal

ize

d C

ou

nts

Incident X-Ray Energy (eV)

XANES Sample FittingRaw Data Data Fit

NbO Powder, 2+ Nb Alloy, Metallic

Nb Powder, Metallic

XANES SETU P A T TH E

SY N C H R OTR O N APS






2 um

• Nb experiences delayed oxidation in comparison

to the Zr matrix.

0.0%

0.2%

0.4%

0.6%

0.8%

1.0%

1.2%

-4 -2 0 2 4

Am

ou

nt

of

Nb

oxi

diz

ed

(w

t%)

Distance from interface

Oxidation Profile Zr-1.0Nb (720C)

M/O O/W

XANES DATA ANALYSIS




• More Nb remains metallic, locked in SPPs, in 580°C Zr1.0Nb oxide

than in 720°C Zr1.0Nb oxide.

• This confirms the TEM/EDS data

• WHY DO WE CARE?

XANES RESU LTS


Zr-1.0Nb (720°C)



2 um

• Rationalization using the Coupled Current Charge Compensation model:

• 1D conservation law for VO.. and 𝑒− :

𝜕𝐽𝑠 𝑥,𝑡

𝜕𝑥+

𝜕𝐶𝑠 𝑥,𝑡

𝜕𝑡= 0

• The interface reactions are at equilibrium.

• The diffusion of oxygen into the metal or suboxide formation ahead of the oxide are

neglected

• The oxide-water and oxide-metal interfaces are planar and the oxide microstructure

homogeneous.

• The coupled-current condition of net zero charge transport through the film at all times.

𝑠

diffusingspecies

𝑍𝑠𝑒𝐽𝑠 = 0, 𝐽𝑠 = 2𝑎𝜈𝑠e−

𝑒𝜁𝑠𝑘𝐵𝑇 𝐶𝑠

𝑘−1e𝑍𝑠𝑒𝑎𝐸𝑘𝑘𝐵𝑇 − 𝐶𝑠

𝑘e−

𝑍𝑠𝑒𝑎𝐸𝑘𝑘𝐵𝑇

• Local space charge at monolayer 𝑘 (hydrogen not modeled, see poster session):

𝜌𝑘 =

𝑠

Allspecies

𝑍𝑠𝐶𝑠𝑘 = 2𝐶VO

..𝑘 − 𝐶e−

𝑘 +

𝑖

Aliovalentions

𝑍𝑖𝐶𝑖𝑘


MO D ELIN G O F NB EFFEC T O N

CO R R O S IO N



2 um

• Space charge 𝝆 𝒙 → local electric field, 𝐸𝑘 :

𝐸𝑘 = 𝐸0 +8𝜋𝑎𝑒

𝜀𝜀0Γ𝑘

𝑙=1

𝑘

2𝐶VO..𝑙 − 𝐶e−

𝑙

with Γ𝑘 = 1 −

𝑙=1

𝑘 σ𝑚=05 4 −𝑚 𝐶

Nb 4−m ′𝑙

2𝐶VO..𝑙 − 𝐶e−

𝑙

• Γ𝑘 is defined as the space charge compensation factor evaluated at the 𝑘th

layer.

• If Γ𝑘 = 0 ⟺ σ𝑚=05 4 −𝑚 𝐶

Nb 4−m ′𝑙 = 2𝐶VO

..𝑙 − 𝐶e−

𝑙 , then local

electroneutrality is achieved thanks to the solute Nb in the oxide

• If Γ𝑘 = 0 ⟹ parabolic kinetics

• Solved using a robust Newton-Raphson method.



CO R R O S IO N



2 um

• C4 model result:


MODELING OF NB EFFECT ON CORROSION

As expected, the ZrNb alloy corrosion

kinetics decreases (and becomes sub-

parabolic) IF LESS Nb IS IN SOLID

SOLUTION to compensate the space charge

13

XANES VS C4



Ok… solute Nb matters for corrosion rate… Do that apply to irradiation?

M. Moorehead, Z. Yu, L. Borrel, Z. Couet, J. Hu, Z. Cai, Comprehensive Investigation of

the Role of Nb on the Oxidation Kinetics of Zr-Nb Alloys, Corrosion Science (2019).


C4 model:For Nb2+:

Γ𝑘 = 0

⟺ 2𝐶Nb2

′𝑙 = 2𝐶VO

..𝑙 − 𝐶e−

𝑙

For Nb3+:

Γ𝑘 = 0 ⟺ 𝐶Nb′𝑙 = 2𝐶VO

..𝑙 − 𝐶e−

𝑙

XANES:

𝑚=0

5

𝐶Nb𝑚

′𝑙

However, XANES is not sensitive enough for:

𝑚=0

5

4 − 𝑚 𝐶Nb 4−m ′𝑙

Zr1.0Nb (720 °C)

135 days

7 days

Nb2′

Nb3′

Nb2′

Nb3′

Nb2′

Nb3′

Nb2′

Nb3′

Zr1.0Nb (580 °C)

7 days

135 days

14

IR R A D IAT IO N EX P ER IM EN TA L SETU P



2MeV Proton Irradiation at University of Wisconsin-Madison

Ion Beam Laboratory

Parameters:

8-10 μA , 1.3x1019 ions/cm2/s, 1.0 dpa, 123 hrs, 350°C

Temperature history

[4] Yu, et al. “Irradiation-Induced Nb Redistribution of ZrNb Alloy: An APT Study.” Journal of Nuclear Materials, vol. 516, 2019, pp. 100–110.

2. Proton irradiation induced Nb redistribution

• 2MeV Proton Irradiation• 20 μA , 6.94E13 ions/cm2s, 1 dpa, 350°C• Indium cooling stage • Temperature control with IR camera (Calibrated)

UW-Madison Ion Beam Laboratory

15

(S)TEM/EDS ON UNIRRADIATED ZR-XNB• Total element composition:

• 570 Cͦ Zr-0.5Nb : αZr + β Nb + Laves phases

• 570 Cͦ Zr-1.0Nb: α Zr + βNb + Laves phases



ppm Nb Fe Al Cr Ni Si

Zr0.5Nb 5270 430 50 30 20 20

Zr1.0Nb 11270 470 40 40 20 10


16

(S)TEM/EDS ON IRRADIATED ZR-XNB

• Irradiated samples were prepared by FIB

• Irradiation induced platelets were found in 1 dpa Zr0.5Nb



FeZr

Nb Cr

STEM BF platelets + native


17

• Irradiation induced platelets were also found in 1 dpa Zr1.0Nb

• There are lots of Nb-rich platelets (max. 40 at.%) for 1 dpa Zr1.0Nb

135 ± 69 nm long 27 ± 12 nm wide

•



BF

30 nm



18

APT CHARACTERIZATION

• APT study on Zr1.0Nb and Zr0.5Nb shows Nb-rich nanoclusters in the

irradiated samples.

• Observation of nanoclusters are consistent with literatures.

• Proton irradiation on Low-Tin ZirloTM by E. Francis [6].

• 4MeV Ni3+ at 573K on J-AlloyTM [7] .



1dpa Zr0.5NbZr1.0Nb

[4] Zefeng Y., Couet A. (2019). JNM

[6] Francis, E., Babu, R., Harte, A., Martin, T., Frankel, R., Jadernas, D., . . . Preuss, M. (2019). Effect of Nb and Fe on damage evolution in a Zr-alloy

during proton and neutron irradiation. Acta Materialia, 165, 603-614.

[7] Matsukawa, Y., Yang, H.L., Saito, K., Murakami, Y., Maruyama, T., Iwai, T., . . . Abe, H. (2016). The effect of crystallographic mismatch on the obstacle

strength of second phase precipitate particles in dispersion strengthening: Bcc Nb particles and nanometric Nb clusters embedded in hcp Zr. ActaMaterialia, 102, 323-332.


19

APT CHARACTERIZATION

• Nb concentration of irradiated Zr-xNb after cluster analysis

Iso-density method is used (but did max. separation as well…, same

results)

• Nb concentration in the solid solution is reduced as irradiation dose

increases. UW Environmental Degradation of Nuclear Materials Laboratory





2 um

• C4 model result:



CO R R O S IO N

As expected, the irradiated ZrNb alloy

corrosion kinetics slowly decreases (and

becomes more and more sub-parabolic)

as less and less Nb is available to

compensate the oxide space charges.

21

DEFECT AT PLATELET/MATRIX INTERFACE

• HRSTEM shows edge dislocations (pointed white arrows) nearby the

two ends of irradiation induced platelets.

• Orientation relationship: 𝟐ഥ𝟏ഥ𝟏𝟎 𝒁𝒓// 𝟏ഥ𝟏𝟏 𝑵𝒃 ; (000ഥ𝟐)Zr // (011)Nb



b

3. Nb redistribution under irradiation mechanism

22

4D-STEM STRAIN MAPPING

• 4D-STEM plots the strain relative to the irradiated Zr matrix.

• Relatively large strain field (yellow regions) were found nearby the two

ends of platelets.



റ𝑔1: റ𝑔2:

B) C)

റ𝑔1: matrix [000ത2] / platelet [011]റ𝑔2: matrix [0ത11ത1] / platelet [ത101]

d-s

pac

ing

(A)

d-s

pac

ing

(A)

റ𝑔1 റ𝑔2

A)

20 nm

3. Nb redistribution under irradiation mechanism

23

SCHEMATIC OF PRECIPITATE GROWTH



Native β-Nb

Strain field

Growth

RecoilDissolution

Matrix

Proton irradiation

+

+

+

+

Enhanced Nb Diffusion

Zr

SoluteResolution

Irradiation induced point defects.

Nucleation of Nb-rich platelet

24

CO N C LU S IO N

• ZrNb Microchemistry analysis :

• Nb is locked into βNb in the oxide, while Nb dissolves from βZr in the oxide.

• More Nb doping in the oxide in βZr containing alloy

• XANES shows that the main oxidation of Nb in the oxide is below 4+

• Effect on corrosion of ZrNb alloys:

• The C4 model reveals that the Nb doping can compensate the space charges:

• Space charge compensation induces faster, parabolic kinetics.

• Effect of irradiation on ZrNb microchemistry and microstructure:

• 2MeV, 350C, 1dpa, proton irradiation induces β Nb-rich platelets

• 2MeV, 350C, 1dpa, proton irradiation induces a reduction of solute Nb

• CONCLUSION: Irradiation of ZrNb results in a decrease of oxidation rate because ofradiation induced/enhanced precipitation, decreasing Nb in solid solution, providing lesscompensation of oxide space charges.

• Need to develop a radiation induced/enhanced precipitation mechanism to predict the Nbsolute depletion rate and evolution of space charge compensation factor.



UW Environmental Degradation of Nuclear Materials Laboratory19th International Symposium on Zirconium in the Nuclear Industry

THANK YOU

26

RESEARCH BACKGROUND AND MOTIVATION



thic

kne

ss

time

[1] Motta, Arthur T., et al. “Corrosion of Zirconium Alloys Used for Nuclear Fuel Cladding.” Annual Review of Materials Research, vol. 45, no. 1, 2015, pp. 311–343.

27

ATO M IC PR O B E TO M O G R A P H Y O N

ZRNB• Nb concentration in the entire needles.

• Nb concentrations are acquired from full 31 Da peak and

deconvoluted 46.5 Da peak by IVAS .

• From ZrNb phase diagram, the maximum solubility limit of Nb is

0.6 at%

• Unirradiated

needles contains

0.3-0.4 at% Nb.

• Despite dose level,

all alloys exhibit Nb

concentration

lower than the bulk

Nb concentration.

III. APT characterization



28

ATOMIC PROBE TOMOGRAPHY ON ZRNB• Fe concentration in the entire needles.

• A) is using the front portion of 28 Da peak, ranging from 27.95 Da to 28.02 Da, to the avoid CO+ contribution.

• B) is using natural isotope of Fe at 27 Da (54Fe2+) with abundance of 5.845 %.


• There is an increase of Fe in

irradiated samples, and rise above

commonly accepted 0.02 at% Fe

in Zr solid solution.

• Fe content is unexpectedly high.

• No obvious trend



29


ZRNB• Nb concentration of irradiated Zr-xNb after cluster analysis

• Max separation, proximity histogram, iso-density.

• The Nb concentration in the solid solution of irradiated samples

are reduced, comparing to unirradiated condition.

• Note: • Bar plots are after

iso-density method. • Ref means “assumed

values”, either based on literature review or thermodynamics prediction.

Ref

Ref






• Corrosion of 1 dpa Zr1.0Nb and 1 dpa Zr0.5Nb

• Oxide thickness is measured from SEM and TEM images.

• Unexpectedly, the irradiated area has slightly higher oxide thickness than

unirradiated area.

VIII. Post-irradiation corrosion

CO R R O S IO N O F P R O TO N

IRRADIATED ZRNB

Zr1.0Nb/Zr0.5Nb7/6 days

Zr1.0Nb/Zr0.5Nb38/37 days

31

• Native precipitates (blue arrow) were survived in 1 dpa Zr1.0Nb



➢ Minimum reduction of Nb concentration in native precipitates to about 60

at.%. Some of native βNb have reduced to 40 at.% or even less.

30 nm

➢ Total particle density is decreasing as dpa

increases.

➢ Native precipitates were suspected to

dissolve upon proton irradiation.


III. Irradiation Experiment

31

2 Mev H+ irradiation, 350ºC

32

570 Cͦ

Zr-0.5Nb

Zr-1.0Nb

Autoclave corrosion at 260 ͦC and 6 MPa

Nb SOLUTE

CONCENTRATION DECREASE

1

2

3

Characterization:APT/(S)TEM/EDS/XANES

PL A N TO TEST HY P OTH ES IS

4 5

6





PR EL IM IN A R Y CO N C LU S IO N S :1. Does Nb distribution and electronic structure in the oxide affect

corrosion kinetics? YES!• Microstructure indeed has an effect on Zr-1.0Nb corrosion kinetics.

• Since βZr dissolve upon oxidation, higher corrosion kinetics of Zr-1.0Nb with βZr is

suspected due to abundance of oxidized Nb, which compensated the space charge in

the oxide.

Hypothesis: Irradiation reduces Nb concentration in α-Zr matrix by

precipitating Nb-rich irradiation-induced platelets resulting in lower corrosion

kinetics

2. Does proton irradiation offer a good surrogate to neutron irradiation in terms of Nb

redistribution?

3. What is the mechanism of irradiation induced Nb redistribution?

4. Does the irradiation induced microstructure of the base metal survive in the oxide

formed by subsequent corrosion?

5. Is the corrosion rate of pre-irradiated ZrNb samples lower than unirradiated materials

and why?



2 um

• Corrosion of 1 dpa Zr1.0Nb and 1 dpa Zr0.5Nb

• Native precipitates (yellow) remains in the oxide for 6/7 days corrosion.

• Nb-rich platelets(red) were found in oxide of 37 days corroded 1 dpa

Zr1.0Nb. Also, they were found in metal.

V. Post-irradiation corrosion

CORROSION OF PROTON IRRADIATED ZRNB

Irradiated area

Unirradiated

BF

37 days corroded 1 dpa Zr1.0Nb

35

UNIRRADIATED SAMPLE CHARACTERIZATIONS

• STEM characterization of unirradiated samples

STEM showing SPPs of electropolished Zr-0.2Nb, Zr-0.4Nb, Zr-0.5Nb, Zr-1.0Nb

Examples of STEM images before and after processing to identify SPPs in Zr-0.2Nb

Effect of irradiation on ZrNb corrosion mechanism

MUZIC-3 meeting EDF, 27th -29th Nov, 2018

36

UNIRRADIATED SAMPLE CHARACTERIZATIONS

• ChemiSTEM characterization of unirradiated samples



• For 1000°C annealed Zr-0.5Nb, there is Nb and Fe enriched lath martensites in α-

Zr matrix.

37

PR O TO N IR R A D IA T IO N O F ZRNB

ALLO YS

• Temperature is well controlled (ASTM standard)


𝐸𝑑𝑍𝑟 = 40eV

𝐸𝑑𝑁𝑏 = 60eV

g = 6.51 g/𝑐𝑚3

Fluence = 1.4E19 ions/𝑐𝑚2


38

• 1.0 dpa irradiated Zr-1.0Nb

• Grains remains recrystallized state. Native particles survived.

• There are multiple Nb-rich needle-like precipitates throughout the

sample at 15 μm depth from irradiation surface.


CH A RA C TER IZAT IO N O F 1.0 DPA ZR 1.0NB

Histogram of length and width of irradiation

induced needle-like precipitates.


3 µm

3 µm 3 µm

39


• HRSTEM shows Burgers orientation relationship of irradiation

induced particle/matrix: (0002) // (011), [1ത11] // [2ത1ത10]

(0002)

{110}

Precipitate

Matrix

(0002)

(0ത111)

(0ത110)

(0ത11ത1)

(0001)

Matrix

(110)

(01ത1)

[2-1-10]

(101)

SPP

OR IEN TAT IO N REL AT IO N SH IP RIP/MATRIX

C14 – Zr[2ത1ത10]

BCC – Nb[1ത11]


40

• 4-D STEM Introduction:

• Using fast electron camera,

imaging mode diffraction

patterns at each scanned

position are recorded at

the same speed of taking

HRSTEM imaging.

• By comparing d-spacings

from captured diffraction

patterns with reference

values, strain maps can be

generated.


4D STEM ON 1.0 DPA ZRNB ALLOYS

Muller-Caspary Knut,http://www.fz-juelich.de/er-c/er-c-1/EN/Forschung/moreSTEM/_node.html

𝜀 =𝑐𝑎𝑝𝑡𝑢𝑟𝑒𝑑 − 𝑟𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒

𝑟𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒


41

• How to generate strain map:

1. From 4-D STEM and HRSTEM images, diffraction patterns at each

imaging pixel size area were obtained.


4D STEM O N 1.0 D PA ZRNB ALLO YS

𝜀 =𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑 − 𝑟𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒

𝑟𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒

2. Choose the planes of interest that

to calculated strain. For now, we use

Ԧ𝑎(0002) and 𝑏(0ത11ത1).

3. Choose the reference values.

• Method 1:Measures the d-spacing of matrix

plane using the captured diffraction

patterns far away from SPP as

references.

• Method 2:Use ideal d-spacing of matrix plane

based on simulated values as

references.


42

II. Effect of irradiation on ZrNb corrosion mechanism


43


ZRNB• Fe concentration in the entire needles.

• Based on literature references, Fe concentrations are acquired

from selecting a portion of the peak below 28.02 Da due to CO

interference.

[5] Thuvander, & Andrén. (2011). Methods of quantitative matrix analysis of Zircaloy-2. Ultramicroscopy, 111(6), 711-714.

[6] Hudson, D., & Smith, George D. W. (2011). Zirconium Oxidation on the Atomic Scale.



dmax = 1.9Order = 5 Nmin = 10

L = 1.5de = L

44

MA X SEPA R AT IO N METH O D• What parameters can affect calculation?

• dmax , order , Nmin , L (set L = 0.75*dmax) , de

• Example:

Zr1.0Nb

1 dpa

Fe Nb Zr

Parameter definition by IVAS manual

Identified clusters Matrix without clusters


0

100

200

300

400

0 2 4

Co

un

ts

distance (nm)

Nearest Neighbor Distribution

Data Random

dmax

0

2

4

6

8

10

6 11 16

Co

un

ts

Ions

Cluster Size Distribution

data random

Nmin


45

ISO CO N C EN TR ATO N METH O D• What parameters can affect calculation?

• Isoconcentration or isodenstiy values

• I used isoconcentration values

• Example: 0.6 0.8

Matrixwithout clusters

Identify clusters

Values：

1dpa Zr1.0Nb



46

PR O X IM IT Y HISTO G R A M METH O D• What parameters can affect calculation?

• Isoconcentration or isodenstiy values

• Recommended to use isodensity values

• Required manual decomposition of overlapping peaks

• Example:

Chose isodensity = 0.6Create concentration profile


Averaged to get at% in solid solution


fundamental understanding of nb effect on corrosion … · 2019-06-26 · • shape of the nb...

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