Research on the corrosion mechanisms of new Zirconium alloys containing Niobium

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Research on the corrosion mechanisms ofResearch on the corrosion mechanisms ofnew Zirconium alloys containing Niobiumnew Zirconium alloys containing Niobium

Student:Student: Zhang HaixiaZhang Haixia

Supervisors:Supervisors: Professor Zhou LianProfessor Zhou Lian Doctor Daniel Fruchart Doctor Daniel Fruchart Professor El Kébir HlilProfessor El Kébir Hlil

Reporters:Reporters: Professor Li ZhongkuiProfessor Li ZhongkuiProfessor Daniel ChateignerProfessor Daniel Chateigner

Examiners:Examiners: Professor Sun JunProfessor Sun JunDoctor Luc Ortega Doctor Luc Ortega

2009. 11. 182009. 11. 18

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ContentsContents• IntroductionIntroduction• Research methodsResearch methods• Corrosion resistance of Zirconium alloysCorrosion resistance of Zirconium alloys• Relationship between the matrix microstructure Relationship between the matrix microstructure

and corrosion resistance of new Zirconium alloysand corrosion resistance of new Zirconium alloys• The effect of the crystal structure oxide film on The effect of the crystal structure oxide film on

corrosion resistancecorrosion resistance• Relationships of the residual stress, crystal Relationships of the residual stress, crystal

structure in oxide film and corrosion resistancestructure in oxide film and corrosion resistance• Corrosion mechanism of new Zirconium alloys Corrosion mechanism of new Zirconium alloys • ConclusionsConclusions

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1. Introduction1. Introduction• Development of nuclear powerDevelopment of nuclear power

At presentAt presentthere are more than 440 nuclear power plantsthere are more than 440 nuclear power plants

in the Worldin the World

19541954the first nuclear power plantthe first nuclear power plant

in USSRin USSR

19571957first commercial nuclear power plantfirst commercial nuclear power plant

in USAin USA

4Fig. 1-1 Fuel assemblies

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• Zirconium alloys used in nuclear reactorZirconium alloys used in nuclear reactor

•• Zr-Sn system alloy Zr-Sn system alloy

★ ★ Zr-1, Zr-2, Zr-4, improved Zr-4Zr-1, Zr-2, Zr-4, improved Zr-4

•• Zr-Nb sytem alloyZr-Nb sytem alloy

★★ E110, M5, Zr-2.5NbE110, M5, Zr-2.5Nb

•• Zr-Sn-Nb system alloyZr-Sn-Nb system alloy

★★ Zirlo, E635, NDA, HANA, NZ2, NZ8Zirlo, E635, NDA, HANA, NZ2, NZ8

1. Introduction1. Introduction

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• Research summary of the water-side corrosion of Research summary of the water-side corrosion of Zirconium alloyZirconium alloy

•• Water chemical effect on corrosion behaviorWater chemical effect on corrosion behavior

• • Heat treatment effect on corrosion behaviorHeat treatment effect on corrosion behavior

• • Alloy composition effect on corrosion behaviorAlloy composition effect on corrosion behavior

★★ MMatrix microstructure (alloying elementsatrix microstructure (alloying elements content, precipitate characteristic);content, precipitate characteristic);

★★ Characteristic of oxide film (crystal structure, stress).Characteristic of oxide film (crystal structure, stress).


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CorrosionCorrosion resistanceresistance

StressesStresses in the oxide in the oxide

filmfilm

Structure Structure of oxide filmof oxide film

MatrixMatrix

microstructuremicrostructure

CompositionComposition(Nb addition)(Nb addition)

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Nb content in the matrixNb content in the matrix Low Nb contents in the matrix is betterLow Nb contents in the matrix is better

Precipitate characteristicPrecipitate characteristic Small and well-distributed β-NbSmall and well-distributed β-Nb can improve the corrosion resistance

Crystal structure of oxide filmCrystal structure of oxide film t-ZrOt-ZrO22 and m-ZrO and m-ZrO22;;

Is a high t-ZrOIs a high t-ZrO2 2 content good to improve corrosion resistance ? content good to improve corrosion resistance ? On the stabilization mechanism of t-ZrOt-ZrO2 2 ??

Stress distribution in the oxide film

High compressive stresses in oxide film How do compressive stresses affect phase transition and corrosion resistance ?


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•• Corrosion mechanismsCorrosion mechanisms

•• Diffuse hypothesisDiffuse hypothesis

•• Dissolving hypothesis Dissolving hypothesis

•• O-Li group cumbering hypothesisO-Li group cumbering hypothesis

•• Barrier hypothesisBarrier hypothesis

•• Phase transformation hypothesisPhase transformation hypothesis

So far, there is no clear understanding of the corrosion So far, there is no clear understanding of the corrosion

mechanisms of mature alloys.mechanisms of mature alloys.


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Research routeResearch route

NZ2, NZ8 alloysNZ2, NZ8 alloys

Blank samplesBlank samples Corroded in static Corroded in static autoclaveautoclave

Samples corrodedSamples corroded

TEM analysisof

size, amount,distribution

andcomposition of

precipitates

Structure ofprecipitatesconfirmed

by neutron diffraction

SEM analysisSEM analysisof oxidesof oxides

morphologiesmorphologies

XRD and RamanXRD and Ramanspectroscopy spectroscopy

of crystal structure, of crystal structure, of phase content, of phase content, of internal stressof internal stress

in oxide filmsin oxide films

To find the relationships of Nb addition, t-ZrO2 content on stress change and corrosion resistance, to confirm the corrosion mechanism of Zirconium alloys

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2. Research methods2. Research methods

• Experimental materialsExperimental materials Elemental compositions of alloys (wt.%)Elemental compositions of alloys (wt.%)

Alloys Sn Nb Fe Cr O ZrAlloys Sn Nb Fe Cr O Zr

Zr-4 1.5 - 0.2 0.1 BalanceZr-4 1.5 - 0.2 0.1 Balance

NZ2 1.0 0.3 0.3 0.1 0.08-0.14 BalanceNZ2 1.0 0.3 0.3 0.1 0.08-0.14 Balance

NZ8 1.0 1.0 0.3 - 0.08-0.14 BalanceNZ8 1.0 1.0 0.3 - 0.08-0.14 Balance

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• Techniques flow of the platesTechniques flow of the plates •• 3 vacuum melting - β forging - β quenching - α hot3 vacuum melting - β forging - β quenching - α hot

rolling (<600rolling (<600℃℃)) •• 3 intermediate annealing and 30-50% cold process 3 intermediate annealing and 30-50% cold process

after every annealing - plates (δ=1mm)after every annealing - plates (δ=1mm) •• final re-crystallization annealing (580 /2h).℃final re-crystallization annealing (580 /2h).℃

Intermediate annealing parameters are respectively Intermediate annealing parameters are respectively 650 /2h, 590 /2h and 590 /2h.℃ ℃ ℃650 /2h, 590 /2h and 590 /2h.℃ ℃ ℃


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• The autoclave experimentsThe autoclave experiments

• • Corrosion conditionsCorrosion conditions ★★ 360 /18.6MPa in pure water;℃360 /18.6MPa in pure water;℃ ★★ 360 /18.6MPa in lithiated water; ℃360 /18.6MPa in lithiated water; ℃ ★★ 400 /10.3MPa in steam.℃400 /10.3MPa in steam.℃

• • MMethod indicating the corrosion degreeethod indicating the corrosion degree ★★ wwtt=10000•(=10000•(WWtt-W-W00)/)/S, WS, W00 is the weight of is the weight of un-corroded sample,un-corroded sample, W Wtt is the weight of corroded sample,is the weight of corroded sample,

S S is the area of sampleis the area of sample, w, wtt is the weight gainis the weight gain..


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•• Analyses and measurementsAnalyses and measurements

•• JEM-200CX transmission electron microscopeJEM-200CX transmission electron microscope

•• Grazing XRD diffractometer - PW3830Grazing XRD diffractometer - PW3830

(Fe, λK(Fe, λKαα=1.9364Å=1.9364Å))

•• Normal XRD diffractometer - PW3830Normal XRD diffractometer - PW3830

(Cu, λK(Cu, λKαα=1.5444Å=1.5444Å))

•• JY-T64000 laser Raman spectrometerJY-T64000 laser Raman spectrometer

•• D1B neutron PSD diffractometerD1B neutron PSD diffractometer (n(n00, λ=2.42Å, λ=2.42Å))

•• JSM-840A scanning electron microscopeJSM-840A scanning electron microscope


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3. Corrosion resistance of Zirconium alloys3. Corrosion resistance of Zirconium alloys

• Corrosion resistance in Corrosion resistance in 360oC lithiated water

0 50 100 150 200 250 300 350 4000

200

400

600

800

1000

1200W

eigh

t G

ain(

mg/

dm2 )

Exposure time(days)

NZ2-360oC Li water

NZ8-360oC Li water

Zr-4-360oC Li water

Fig. 3-1 Corrosion kinetics of NZ2, NZ8 and Zr-4 alloys in 360oC lithiated water

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• Corrosion resistance in 400Corrosion resistance in 400ooC steamC steam

0 100 200 300 4000

60

120

180

240

300

transition point

transition point

Wei

ght G

ain(

mg/

dm2 )

Exposure time(days)

NZ2-400oC steam

NZ8-400oC steam

Fig. 3-2 Corrosion kinetics of NZ2, NZ8 alloys investigated in 400oC steam


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• Corrosion kinetics of NZ2 alloy in different mediaCorrosion kinetics of NZ2 alloy in different media

0 50 100 150 200 250 300 350 400102030405060708090

100110120130140150160

Wei

ght

Gai

n(m

g/dm

2 )

Exposure time(days)

NZ2-360oC pure water

NZ2-360oC Li water

NZ2-400oC steam

Fig. 3-3 Corrosion kinetics of NZ2 alloy investigated in different mediums


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• SummarySummary

•• Nb addition reveals good to improve corrosion Nb addition reveals good to improve corrosion

resistance of Zirconium alloysresistance of Zirconium alloys

•• In both media, corrosion resistance of NZ2 alloy isIn both media, corrosion resistance of NZ2 alloy is better than of NZ8 alloybetter than of NZ8 alloy

•• Oxide thickness at transition point is 2~3μmOxide thickness at transition point is 2~3μm


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4. Relationship of the matrix microstructure and 4. Relationship of the matrix microstructure and corrosion resistance of new Zirconium alloyscorrosion resistance of new Zirconium alloys• Matrix microstructure of NZ2Matrix microstructure of NZ2

Element at% Cr 8.76Fe 35.75Zr 55.49

Element at% Cr 8.47Fe 36.76Zr 43.42Nb 11.35

(a) (b)

(c) (d)

200nm 200nm

Fig. 4-1 TEM images of NZ2 alloy matrix and the EDS result of the precipitates ( （ b ） is the dark image)

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Fig. 4-2 (a) TEM images of NZ8 alloy matrix, (b) corresponding dark image,(c) EDS analysis of precipitates

4. Relationship of the matrix microstructure and 4. Relationship of the matrix microstructure and corrosion resistance of new Zirconium alloyscorrosion resistance of new Zirconium alloys

Element at% Fe 9.05 Zr 82.34 Nb 8.60

(a)

(c)

(b) 500nm 500nm

•• Matrix microstructure of NZ8Matrix microstructure of NZ8

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30 40 50 60 70 80 90 100 110

200000

400000

600000

800000

1000000

1200000Z

r(11

0)

Zr(

102)

Zr(

101)Z

r(00

2)

Inte

nsit

y(a.

u.)

2 Theta ( o )

50 55 60 65 70 75

40000

50000

60000

Zr(

100)

Zr(

Fe,

Cr)

2 (20

1)

40 60 80 100

20000

40000

60000

80000

100000

120000

140000

Inte

nsi

ty(a

.u.)

2 Theta ( o )

Zr(

110)

Zr(

102)

Zr(

101)

Zr(

002)

50 55 60 65 70 7518000190002000021000220002300024000250002600027000280002900030000


Fig. 4-3 Neutron diffraction patternof NZ2 alloy matrix

Fig. 4-4 Neutron diffraction pattern of NZ8 alloy matrix

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• Summary Summary

• • Nb content in the matrixNb content in the matrix

• • Oxidation characteristicsOxidation characteristics

•• Type and volume fraction of precipitates.Type and volume fraction of precipitates.


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5. Oxide film crystal structure effect5. Oxide film crystal structure effecton corrosion resistanceon corrosion resistance

• Crystal structure of NZ2 alloy oxide filmCrystal structure of NZ2 alloy oxide film

20 40 60 800

50

100

150

200

250

300

M(1

11)

T(1

01)

D

CBA

Inte

nsi

ty (

a.u

.)

2 Theta ( o )

A: 3d-0.2o

B: 3d-0.3o

C: 3d-0.5o

D: 3d-1.0o

Fig. 5-1 Grazing incidence XRD patterns of oxide films surface of NZ2 alloys

exposed to 360oC lithiated water for 3 d

20 40 60 800

200

400

600

800

1000

1200

1400

CBA

M(1

11)

T(1

01)

Inte

nsi

ty (

a.u

.)

2 Theta ( o )

A: 3d-0.3o

B: 3d-0.5o

C: 3d-1.0o

Fig. 5-2 Grazing incidence XRD patterns of oxide films surface of NZ2 alloys

exposed to 400oC steam for 3 d

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Fig. 5-3 Normal XRD spectrum of oxide films of NZ2 alloys exposed to 360oC

lithiated water for different times

Fig. 5-4 Normal XRD spectrum of oxide films of NZ2 alloys exposed to 400oC

steam for different times


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Fig. 5-5 Relation of corrosion time and t-ZrO2 content in oxide films of NZ2 alloys corroded in 360oC lithiated water and 400oC steam


T-ZrOT-ZrO22 content obtained from XRD data content obtained from XRD data

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200 400 60020003000400050006000700080009000

100001100012000130001400015000160001700018000

2.8

1.2

1.00.2

Inte

nsi

ty (

a.u

.)

Wavenumber (cm-1)

T

Surface

Interface

Thickness/m

200 400 6002000

4000

6000

8000

10000

12000

14000

16000

TT Interface

Surface

Inte

nsi

ty (

a.u

.)

Wavenumber (cm-1)

1.8

1.4

1.0

0.60.2

Thickness/m

Fig. 5-6 Raman spectra of oxidized films at difference distances from surface, which results exposing NZ2 alloysto 360oC lithiated water for 70 d


Fig. 5-7 Raman spectra of oxidized films at difference distances from surface, which results exposing NZ2 alloys

to 400oC steam for 70 d

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Fig. 5-13 SEM image of oxide films of NZ2 alloys exposed to 360oC lithiated

water for 3 d

Fig. 5-14 SEM image of oxide films of NZ2 alloys exposed to 360oC lithiated

water for 126 d


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• SummarySummary •• T-ZrOT-ZrO22, m-ZrO, m-ZrO22

T-ZrOT-ZrO22 content decreases gradually content decreases gradually

•• C-ZrOC-ZrO22 appears when the oxide film thickness appears when the oxide film thickness

reaches about 2μmreaches about 2μm

•• T-ZrOT-ZrO22→→m-ZrOm-ZrO22, t-ZrO, t-ZrO22→→c-ZrOc-ZrO22→→m-ZrOm-ZrO22

• • T-ZrOT-ZrO2 2 content is the highest at the oxide/metalcontent is the highest at the oxide/metal

interfaceinterface

• • The high t-ZrOThe high t-ZrO22 content can improve the corrosion content can improve the corrosion

resistanceresistance


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6. Relationships of the residual stresses, crystal 6. Relationships of the residual stresses, crystal structure in oxide films and corrosion resistancestructure in oxide films and corrosion resistance

• IntroductionIntroduction

The stresses mainly result from volume changes of The stresses mainly result from volume changes of metal and oxide, of the phase transformation from t-metal and oxide, of the phase transformation from t-ZrOZrO22 to m-ZrO to m-ZrO22, of the oxidation of the precipitates , of the oxidation of the precipitates

The stresses affect the stabilization of the oxide films, The stresses affect the stabilization of the oxide films, and change the diffusion coefficientand change the diffusion coefficientThen, the corrosion kinetics is changed. Then, the corrosion kinetics is changed.

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•• Experimental methodExperimental method

Microstrains are given by the relation:Microstrains are given by the relation:

By the ‹sinBy the ‹sin22ψψ› method, the diffraction peak shift can be › method, the diffraction peak shift can be described as follows:described as follows:

We can get the formula from above two relations: We can get the formula from above two relations:

So So σσ1111 is deduced from the slope p of the is deduced from the slope p of the dd-sin-sin22ψψ line: line:

)22(cot2

1)( 00

0

0

gd

ddhkl

][tan360

)()]2sin(sin[tan360

)2

1(22 22110113

211020

SS

00112

110

2sin)

1( dd

Ed

Ed

110)1

( d

Ep

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• Experimental resultsExperimental results

Fig. 6-1 The d=f (sin2ψ) plots for samples corroded in 360oC lithiated waterfor 14 d., 70 d., 126 d. and 210 d.

Fig. 6-2 The d=f (sin2ψ) plots for samples corroded in 400oC steamfor 3 d., 28 d., 42 d. and 154 d.

32Fig. 6-3 Relationship of the oxide film thickness and compressive stresses in

oxide films of NZ2 alloy corroded at 360oC lithiated water and at 400oC in steam


Kinetic transitionKinetic transition

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• Analysis and discussionAnalysis and discussion •• The kinetics transition is associated with a sudden The kinetics transition is associated with a sudden

stress releasestress release

• • The higher t-ZrOThe higher t-ZrO22 content corresponds to the content corresponds to the

higher compressive stress as a whole.higher compressive stress as a whole.

• • The average t-ZrOThe average t-ZrO22 content decreases content decreases

continuously and smoothly, independent of the continuously and smoothly, independent of the kinetic transitionskinetic transitions


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• The corrosion mechanism of new Zirconium The corrosion mechanism of new Zirconium alloysalloys

• • Oxidation of the matrix and alloying element(s)Oxidation of the matrix and alloying element(s) •• Differential oxidation of precipitates inside the oxideDifferential oxidation of precipitates inside the oxide layerslayers •• Oxidation of Nb in the precipitates, formation of Oxidation of Nb in the precipitates, formation of

vacancy clusters, transformation of t-ZrOvacancy clusters, transformation of t-ZrO22 to c-ZrO to c-ZrO22

• • Cracks form and compressive stresses are releasedCracks form and compressive stresses are released•• Kinetics transition happens. Kinetics transition happens.

7. Investigation of corrosion mechanism of 7. Investigation of corrosion mechanism of new Zirconium alloys containing niobiumnew Zirconium alloys containing niobium

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(a)

(b)

(c)

(d)

Oxide sub-layer rich in t-Oxide sub-layer rich in t-

ZrOZrO22

T-ZrO2 C-ZrO2

Precipitated oxidized fullyPrecipitated oxidized fully

Precipitated oxidized partiallyPrecipitated oxidized partially

Precipitated unoxidizedPrecipitated unoxidized

Fig. 7-4 Model of corrosion mechanism of new Zirconium alloys

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ConclusionsConclusions

• Appropriate Nb addition makes benefit to improve the Appropriate Nb addition makes benefit to improve the corrosion resistance of Zirconium alloys. The corrosion corrosion resistance of Zirconium alloys. The corrosion resistance of NZ2 is better than that of NZ8resistance of NZ2 is better than that of NZ8

• Low Nb content in matrix and a small quantity of Low Nb content in matrix and a small quantity of precipitates with small size are benefit to improve the precipitates with small size are benefit to improve the corrosion resistancecorrosion resistance

• The oxide films are mainly composed of m-ZrOThe oxide films are mainly composed of m-ZrO22 and t- and t-ZrOZrO22 mainly. When the oxide thickness reaches to mainly. When the oxide thickness reaches to 2μm, the c-ZrO2μm, the c-ZrO22 appears appears

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• There are two kinds of phase transformations during There are two kinds of phase transformations during corrosion:corrosion:

t-ZrOt-ZrO22→m-ZrO→m-ZrO22 and t-ZrO and t-ZrO22→c-ZrO→c-ZrO22→m-ZrO→m-ZrO22

• T-ZrOT-ZrO22 is stabilized by the compressive stresses and is stabilized by the compressive stresses and vacancies, and c-ZrOvacancies, and c-ZrO22 is stabilized by vacancies is stabilized by vacancies

• The average t-ZrOThe average t-ZrO22 content decreases continuously content decreases continuously and smoothly, independent of the kinetic transitions as and smoothly, independent of the kinetic transitions as the oxidation proceededthe oxidation proceeded


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• High compressive stresses occur in oxide filmsHigh compressive stresses occur in oxide films

• Sudden release of the compressive stresses in oxide films is related Sudden release of the compressive stresses in oxide films is related to corrosion transition to corrosion transition

• High t-ZrOHigh t-ZrO22 content and compressive stresses in the oxide films content and compressive stresses in the oxide films can improve the corrosion resistance of Zirconium alloys can improve the corrosion resistance of Zirconium alloys

• These new alloys candidate for new generation These new alloys candidate for new generation long life nuclear power plantslong life nuclear power plants


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Many thanks for your attention!Many thanks for your attention!

Documents

Research on the corrosion mechanisms of new Zirconium alloys containing Niobium