1 Research on the corrosion mechanisms of new Zirconium alloys containing Niobium Student:Zhang Haixia Supervisors:Professor Zhou Lian Doctor Daniel Fruchart Doctor Daniel Fruchart Professor El Kébir Hlil Professor El Kébir Hlil Reporters:Professor Li Zhongkui Professor Daniel Chateigner Examiners:Professor Sun Jun Doctor Luc Ortega

2 Contents Contents IntroductionIntroduction Research methodsResearch methods Corrosion resistance of Zirconium alloysCorrosion resistance of Zirconium alloys Relationship between the matrix microstructure and corrosion resistance of new Zirconium alloysRelationship between the matrix microstructure and corrosion resistance of new Zirconium alloys The effect of the crystal structure oxide film on corrosion resistanceThe effect of the crystal structure oxide film on corrosion resistance Relationships of the residual stress, crystal structure in oxide film and corrosion resistanceRelationships of the residual stress, crystal structure in oxide film and corrosion resistance Corrosion mechanism of new Zirconium alloysCorrosion mechanism of new Zirconium alloys ConclusionsConclusions

3 1. Introduction Development of nuclear powerDevelopment of nuclear power At present there are more than 440 nuclear power plants in the World 1954 the first nuclear power plant in USSR 1957 first commercial nuclear power plant in USA

4 Fig. 1-1 Fuel assemblies

5 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-4 ★ Zr-1, Zr-2, Zr-4, improved Zr-4 Zr-Nb sytem alloy Zr-Nb sytem alloy ★ E110, M5, Zr-2.5Nb ★ E110, M5, Zr-2.5Nb Zr-Sn-Nb system alloy Zr-Sn-Nb system alloy ★ Zirlo, E635, NDA, HANA, NZ2, NZ8 ★ Zirlo, E635, NDA, HANA, NZ2, NZ8 1. Introduction

6 Research summary of the water-side corrosion of Zirconium alloyResearch summary of the water-side corrosion of Zirconium alloy Water chemical effect on corrosion behavior Water chemical effect on corrosion behavior Heat treatment effect on corrosion behavior Heat treatment effect on corrosion behavior Alloy composition effect on corrosion behavior Alloy composition effect on corrosion behavior ★ Matrix microstructure (alloying elements ★ Matrix microstructure (alloying elements content, precipitate characteristic); content, precipitate characteristic); ★ Characteristic of oxide film (crystal structure, stress). ★ Characteristic of oxide film (crystal structure, stress). 1. Introduction

7 Corrosion resistance resistance Stresses in the oxide in the oxidefilm Structure of oxide film MatrixmicrostructureComposition (Nb addition)

8 Nb content in the matrix Nb content in the matrix Low Nb contents in the matrix is better Low Nb contents in the matrix is better Precipitate characteristic Precipitate characteristic Small and well-distributed β-Nb Small and well-distributed β-Nb can improve the corrosion resistance Crystal structure of oxide film t-ZrO 2 and m-ZrO 2 ; t-ZrO 2 and m-ZrO 2 ; Is a high t-ZrO 2 content good to improve corrosion resistance ? Is a high t-ZrO 2 content good to improve corrosion resistance ? t-ZrO 2 ? On the stabilization mechanism of t-ZrO 2 ? Stress distribution in the oxide film High compressive stresses in oxide film How do compressive stresses affect phase transition and corrosion resistance ? 1. Introduction

9 Corrosion mechanisms Corrosion mechanisms Diffuse hypothesis Diffuse hypothesis Dissolving hypothesis Dissolving hypothesis O-Li group cumbering hypothesis O-Li group cumbering hypothesis Barrier hypothesis Barrier hypothesis Phase transformation hypothesis Phase transformation hypothesis So far, there is no clear understanding of the corrosion mechanisms of mature alloys. 1. Introduction

10 Research route NZ2, NZ8 alloys NZ2, NZ8 alloys Blank samples Corroded in static autoclave Samples corroded Samples corroded TEM analysis of size, amount, distribution and composition of precipitates Structure of precipitates confirmed by neutron diffraction SEM analysis of oxides morphologies XRD and Raman spectroscopy of crystal structure, of phase content, of internal stress in oxide films To find the relationships of Nb addition, t-ZrO 2 content on stress change and corrosion resistance, to confirm the corrosion mechanism of Zirconium alloys

11 2. Research methods Experimental materialsExperimental materials Elemental compositions of alloys (wt.%) Elemental compositions of alloys (wt.%) Alloys Sn Nb Fe Cr O Zr Zr Balance NZ Balance NZ Balance

12 Techniques flow of the platesTechniques flow of the plates 3 vacuum melting - β forging - β quenching - α hot 3 vacuum melting - β forging - β quenching - α hot rolling (<600 ℃ ) rolling (<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 650 ℃ /2h, 590 ℃ /2h and 590 ℃ /2h. 2. Research methods

13 The autoclave experimentsThe autoclave experiments Corrosion conditions Corrosion 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. Method indicating the corrosion degree Method indicating the corrosion degree ★ w t =10000(W t -W 0 )/S, W 0 is the weight of ★ w t =10000(W t -W 0 )/S, W 0 is the weight of un-corroded sample, W t is the weight of corroded sample, un-corroded sample, W t is the weight of corroded sample, S is the area of sample, w t is the weight gain. S is the area of sample, w t is the weight gain. 2. Research methods

14 Analyses and measurements Analyses and measurements JEM-200CX transmission electron microscope JEM-200CX transmission electron microscope Grazing XRD diffractometer - PW3830 Grazing XRD diffractometer - PW3830 (Fe, λK α =1.9364Å) Normal XRD diffractometer - PW3830 Normal XRD diffractometer - PW3830 (Cu, λK α =1.5444Å) JY-T64000 laser Raman spectrometer JY-T64000 laser Raman spectrometer D1B neutron PSD diffractometer D1B neutron PSD diffractometer (n 0, λ=2.42Å) (n 0, λ=2.42Å) JSM-840A scanning electron microscope JSM-840A scanning electron microscope 2. Research methods

15 3. Corrosion resistance of Zirconium alloys Corrosion resistance inCorrosion resistance in 360 o C lithiated water Fig. 3-1 Corrosion kinetics of NZ2, NZ8 and Zr-4 alloys in 360 o C lithiated water

16 Corrosion resistance in 400 o C steamCorrosion resistance in 400 o C steam Fig. 3-2 Corrosion kinetics of NZ2, NZ8 alloys investigated in 400 o C steam 3. Corrosion resistance of Zirconium alloys

17 Corrosion kinetics of NZ2 alloy in different mediaCorrosion kinetics of NZ2 alloy in different media Fig. 3-3 Corrosion kinetics of NZ2 alloy investigated in different mediums 3. Corrosion resistance of Zirconium alloys

18 SummarySummary Nb addition reveals good to improve corrosion Nb addition reveals good to improve corrosion resistance of Zirconium alloys resistance of Zirconium alloys In both media, corrosion resistance of NZ2 alloy is In both media, corrosion resistance of NZ2 alloy is better than of NZ8 alloy better than of NZ8 alloy Oxide thickness at transition point is 2~3μm Oxide thickness at transition point is 2~3μm 3. Corrosion resistance of Zirconium alloys

19 4. Relationship of the matrix microstructure and corrosion resistance of new Zirconium alloys Matrix microstructure of NZ2Matrix microstructure of NZ2 Element at% Cr 8.76 Fe Zr Element at% Cr 8.47 Fe Zr Nb (a)(b) (c)(d) 200nm Fig. 4-1 TEM images of NZ2 alloy matrix and the EDS result of the precipitates ( （ b ） is the dark image)

20 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 corrosion resistance of new Zirconium alloys Element at% Fe 9.05 Zr Nb 8.60 (a) (c) (b) 500nm Matrix microstructure of NZ8 Matrix microstructure of NZ8

21 4. Relationship of the matrix microstructure and corrosion resistance of new Zirconium alloys Fig. 4-3 Neutron diffraction pattern of NZ2 alloy matrix Fig. 4-4 Neutron diffraction pattern of NZ8 alloy matrix

22 SummarySummary Nb content in the matrix Nb content in the matrix Oxidation characteristics Oxidation characteristics Type and volume fraction of precipitates. Type and volume fraction of precipitates. 4. Relationship of the matrix microstructure and corrosion resistance of new Zirconium alloys

23 5. Oxide film crystal structure effect on corrosion resistance Crystal structure of NZ2 alloy oxide filmCrystal structure of NZ2 alloy oxide film Fig. 5-1 Grazing incidence XRD patterns of oxide films surface of NZ2 alloys exposed to 360 o C lithiated water for 3 d Fig. 5-2 Grazing incidence XRD patterns of oxide films surface of NZ2 alloys exposed to 400 o C steam for 3 d

24 Fig. 5-3 Normal XRD spectrum of oxide films of NZ2 alloys exposed to 360 o C lithiated water for different times Fig. 5-4 Normal XRD spectrum of oxide films of NZ2 alloys exposed to 400 o C steam for different times 5. Oxide film crystal structure effect on corrosion resistance

25 Fig. 5-5 Relation of corrosion time and t-ZrO 2 content in oxide films of NZ2 alloys corroded in 360 o C lithiated water and 400 o C steam 5. Oxide film crystal structure effect on corrosion resistance T-ZrO 2 content obtained from XRD data

26 Fig. 5-6 Raman spectra of oxidized films at difference distances from surface, which results exposing NZ2 alloys to 360 o C lithiated water for 70 d 5. Oxide film crystal structure effect on corrosion resistance Fig. 5-7 Raman spectra of oxidized films at difference distances from surface, which results exposing NZ2 alloys to 400 o C steam for 70 d

27 Fig SEM image of oxide films of NZ2 alloys exposed to 360 o C lithiated water for 3 d Fig SEM image of oxide films of NZ2 alloys exposed to 360 o C lithiated water for 126 d 5. Oxide film crystal structure effect on corrosion resistance

28 SummarySummary T-ZrO 2, m-ZrO 2 T-ZrO 2, m-ZrO 2 T-ZrO 2 content decreases gradually T-ZrO 2 content decreases gradually C-ZrO 2 appears when the oxide film thickness C-ZrO 2 appears when the oxide film thickness reaches about 2μm reaches about 2μm T-ZrO 2 →m-ZrO 2, t-ZrO 2 →c-ZrO 2 →m-ZrO 2 T-ZrO 2 →m-ZrO 2, t-ZrO 2 →c-ZrO 2 →m-ZrO 2 T-ZrO 2 content is the highest at the oxide/metal T-ZrO 2 content is the highest at the oxide/metal interface interface The high t-ZrO 2 content can improve the corrosion The high t-ZrO 2 content can improve the corrosion resistance resistance 5. Oxide film crystal structure effect on corrosion resistance

29 6. Relationships of the residual stresses, crystal structure in oxide films and corrosion resistance IntroductionIntroduction The stresses mainly result from volume changes of metal and oxide, of the phase transformation from t- ZrO 2 to m-ZrO 2, of the oxidation of the precipitates The stresses mainly result from volume changes of metal and oxide, of the phase transformation from t- ZrO 2 to m-ZrO 2, of the oxidation of the precipitates The stresses affect the stabilization of the oxide films, and change the diffusion coefficient The stresses affect the stabilization of the oxide films, and change the diffusion coefficient Then, the corrosion kinetics is changed.

30 6. Relationships of the residual stresses, crystal structure in oxide films and corrosion resistance Experimental method Experimental method Microstrains are given by the relation: Microstrains are given by the relation: By the ‹sin 2 ψ› method, the diffraction peak shift can be described as follows: By the ‹sin 2 ψ› method, the diffraction peak shift can be described as follows: We can get the formula from above two relations: We can get the formula from above two relations: So σ 11 is deduced from the slope p of the d-sin 2 ψ line: So σ 11 is deduced from the slope p of the d-sin 2 ψ line:

31 Experimental resultsExperimental results Fig. 6-1 The d=f (sin 2 ψ) plots for samples corroded in 360 o C lithiated water for 14 d., 70 d., 126 d. and 210 d. Fig. 6-2 The d=f (sin 2 ψ) plots for samples corroded in 400 o C steam for 3 d., 28 d., 42 d. and 154 d.

32 Fig. 6-3 Relationship of the oxide film thickness and compressive stresses in oxide films of NZ2 alloy corroded at 360 o C lithiated water and at 400 o C in steam 6. Relationships of the residual stresses, crystal structure in oxide films and corrosion resistance Kinetic transition

33 Analysis and discussionAnalysis and discussion The kinetics transition is associated with a sudden The kinetics transition is associated with a sudden stress release stress release The higher t-ZrO 2 content corresponds to the The higher t-ZrO 2 content corresponds to the higher compressive stress as a whole. higher compressive stress as a whole. The average t-ZrO 2 content decreases The average t-ZrO 2 content decreases continuously and smoothly, independent of the continuously and smoothly, independent of the kinetic transitions kinetic transitions 6. Relationships of the residual stresses, crystal structure in oxide films and corrosion resistance

34 The corrosion mechanism of new Zirconium alloysThe corrosion mechanism of new Zirconium alloys Oxidation of the matrix and alloying element(s) Oxidation of the matrix and alloying element(s) Differential oxidation of precipitates inside the oxide Differential oxidation of precipitates inside the oxide layers layers Oxidation of Nb in the precipitates, formation of vacancy clusters, transformation of t-ZrO 2 to c-ZrO 2 Oxidation of Nb in the precipitates, formation of vacancy clusters, transformation of t-ZrO 2 to c-ZrO 2 Cracks form and compressive stresses are released Cracks form and compressive stresses are released Kinetics transition happens. Kinetics transition happens. 7. Investigation of corrosion mechanism of new Zirconium alloys containing niobium

35 (a) (b) (c) (d) Oxide sub-layer rich in t- ZrO 2 T-ZrO 2 C-ZrO 2 Precipitated oxidized fully Precipitated oxidized partially Precipitated unoxidized Fig. 7-4 Model of corrosion mechanism of new Zirconium alloys

36 Conclusions Appropriate Nb addition makes benefit to improve the corrosion resistance of Zirconium alloys. The corrosion resistance of NZ2 is better than that of NZ8Appropriate Nb addition makes benefit to improve the corrosion resistance of Zirconium alloys. The corrosion resistance of NZ2 is better than that of NZ8 Low Nb content in matrix and a small quantity of precipitates with small size are benefit to improve the corrosion resistanceLow Nb content in matrix and a small quantity of precipitates with small size are benefit to improve the corrosion resistance The oxide films are mainly composed of m-ZrO 2 and t- ZrO 2 mainly. When the oxide thickness reaches to 2μm, the c-ZrO 2 appearsThe oxide films are mainly composed of m-ZrO 2 and t- ZrO 2 mainly. When the oxide thickness reaches to 2μm, the c-ZrO 2 appears

37 There are two kinds of phase transformations during corrosion:There are two kinds of phase transformations during corrosion: t-ZrO 2 →m-ZrO 2 and t-ZrO 2 →c-ZrO 2 →m-ZrO 2 T-ZrO 2 is stabilized by the compressive stresses and vacancies, and c-ZrO 2 is stabilized by vacanciesT-ZrO 2 is stabilized by the compressive stresses and vacancies, and c-ZrO 2 is stabilized by vacancies The average t-ZrO 2 content decreases continuously and smoothly, independent of the kinetic transitions as the oxidation proceededThe average t-ZrO 2 content decreases continuously and smoothly, independent of the kinetic transitions as the oxidation proceeded Conclusions

38 High compressive stresses occur in oxide filmsHigh compressive stresses occur in oxide films Sudden release of the compressive stresses in oxide films is related to corrosion transitionSudden release of the compressive stresses in oxide films is related to corrosion transition High t-ZrO 2 content and compressive stresses in the oxide films can improve the corrosion resistance of Zirconium alloysHigh t-ZrO 2 content and compressive stresses in the oxide films can improve the corrosion resistance of Zirconium alloys These new alloys candidate for new generation long life nuclear power plantsThese new alloys candidate for new generation long life nuclear power plants Conclusions

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