Mechanical Degradation in Oxides Formed on Zirconium Alloys

319 Pages·2014·9.5 MB·English

by  Philip Platt

Mechanical Degradation
in Oxides Formed on
Zirconium Alloys
A thesis submitted to The University of
Manchester for the degree of Doctor of
Engineering in the Faculty of Engineering
and Physical Sciences

Philip Platt
2014

School of Materials
2
Contents
1. Introduction ................................................................................................................................... 17
1.1 Alternative Submission Thesis Overview ................................................................................ 17
1.2 EngD Overview ........................................................................................................................ 18
2. Industrial Application ..................................................................................................................... 18
2.1 Introduction .............................................................................................................................. 18
2.2 Nuclear and UK Energy ........................................................................................................... 19
2.2.1 Energy Policy and the Market ....................................................................................... 19
2.2.2 Barriers to Nuclear Energy ............................................................................................ 21
2.2.3 Nuclear New Build ......................................................................................................... 22
2.3 Zirconium in the UK Nuclear Industry ...................................................................................... 22
2.3.1 Application in Reactors ................................................................................................. 22
2.3.2 Supply Chain and Manufacturing .................................................................................. 23
2.3.3 Research and Development .......................................................................................... 23
2.3.4 Thesis Value to Amec ................................................................................................... 24
3. Literature Review .......................................................................................................................... 25
3.1 Fundamentals of Zirconium Alloy Oxidation ............................................................................ 25
3.1.1 Introduction .................................................................................................................... 25
3.1.2 Zirconium Alloy Base Metal ........................................................................................... 25
3.1.3 Fundamental Oxidation Issues ...................................................................................... 27
Stage 1: Initial Oxidation ............................................................................................................ 28
Stage 2: Reduced Oxidation Rate ............................................................................................. 29
Stage 3: Transition Window ....................................................................................................... 32
Stage 4: Post Transition & Breakaway ...................................................................................... 33
3.2 Bulk Mechanisms for Oxide Degradation ................................................................................ 40
3.2.1 Creep in α-Zr ................................................................................................................. 40
Overview of Creep in α-Zr .......................................................................................................... 40
Stress Exponents and Creep Transitions .................................................................................. 40
Low Stress Creep Mechanisms ................................................................................................. 41
Effect of Alloy Elements and Impurities ..................................................................................... 46
3.2.2 Oxidation Induced Deformation ..................................................................................... 48
3.2.3 Impact of Applied Stress on Corrosion Kinetics ............................................................ 49
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3.2.4 Creep in ZrO ................................................................................................................ 51
2
Overview of Creep in Manufactured Zirconia ............................................................................ 51
Defining Creep in Naturally Forming Oxides ............................................................................. 51
3.2.5 Hydrogen Induced Lattice Strain .................................................................................. 52
3.3 Surface Roughness and Oxidation ......................................................................................... 53
3.3.1 Overview ....................................................................................................................... 53
3.3.2 Experimental Research................................................................................................. 53
3.3.3 Mathematical and Finite Element Analysis ................................................................... 54
3.4 Metal-Oxide Interface Undulations .......................................................................................... 57
3.4.1 Overview ....................................................................................................................... 57
3.4.2 Experimental Research................................................................................................. 58
3.4.3 Finite Element Analysis................................................................................................. 60
3.4.4 The Impact of Material Properties ................................................................................. 61
3.5 Tetragonal to Monoclinic Phase Transformation .................................................................... 62
3.5.1 Introduction to the Phase Transformation .................................................................... 62
3.5.2 Tetragonal Phase Stabilisation ..................................................................................... 62
Hydrostatic Pressure ................................................................................................................. 62
Grain Size .................................................................................................................................. 63
Alloy Doping Effect .................................................................................................................... 64
Oxygen Vacancies ..................................................................................................................... 65
3.5.3 Destabilisation of the Tetragonal Phase ....................................................................... 65
3.5.4 Impact of the Phase Transformation ............................................................................. 66
4. Methods & Procedures ................................................................................................................. 69
4.1 Materials .................................................................................................................................. 69
4.2 Heat Treatment ....................................................................................................................... 69
4.3 Oxidation ................................................................................................................................. 70
4.4 Synchrotron X-Ray Diffraction (S-XRD) .................................................................................. 71
4.5 Scanning Electron Microscopy (SEM) .................................................................................... 73
4.6 Abaqus Finite Element Analysis (FEA) ................................................................................... 75
4.6.1 Model Constructions ..................................................................................................... 76
Oxidation Induced Deformation (Proposed Paper 1) ................................................................ 76
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Interface Undulations (Proposed Paper 3) ................................................................................ 79
Tetragonal to Monoclinic Phase Transformation (Proposed Paper 5) ...................................... 82
4.6.2 Element Assignment & Convergence ........................................................................... 84
4.6.3 Validation & Verification ................................................................................................ 86
5. Results and Discussion ................................................................................................................. 89
6. Thesis Summary ......................................................................................................................... 215
6.1 Final Hypothesis .................................................................................................................... 217
6.2 Future Work ........................................................................................................................... 218
7. Thesis References ...................................................................................................................... 220
ppendix 1 ......................................................................................................................................... 237
Mesh sensitivity ........................................................................................................................ 237
Oxidation Induced Deformation (Proposed Paper 1) ............................................................... 237
Interface Undulations (Proposed Paper 3) .............................................................................. 240
Tetragonal to Monoclinic Phase Transformation (Proposed Paper 5) .................................... 242
Appendix 2 ...................................................................................................................................... 245
Abaqus Example Input Files ........................................................................................................ 245
Oxidation Induced Deformation (Proposed Paper 1) ............................................................... 245
Interface Undulations (Proposed Paper 3): Axisymmetric ....................................................... 305
Interface Undulations (Proposed Paper 3): 3D ........................................................................ 310
Tetragonal to Monoclinic Phase Transformation (Proposed Paper 5) .................................... 316

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List of Tables: Thesis
Table 1 Chemical Compositions for Zirconium Alloys (wt%) (Chemelle & Knorr 1983; Yoshitaka
Nishino 1996). ................................................................................................................................... 26
Table 2 Definition of transition points for oxidising zirconium alloys ................................................ 35
Table 3 Reported stress values for oxide formed on zirconium alloys ............................................. 37
Table 4 Recorded tetragonal phase fractions for oxides formed on zirconium alloys ...................... 39
Table 5 Summary of Grain Boundary Diffusion Activation Energy for Zirconium Alloys. ................. 45
Table 6 Chemical compositions and conditions for zirconium alloys. .............................................. 69
List of Tables: Proposed Paper 1
Table 1 Chemical compositions for zirconium alloys (wt%) ........................................................... 107
Table 2 Elastic properties [5] .......................................................................................................... 107
Table 3 Summary of grain boundary diffusion activation energy for zirconium alloys ................... 107
List of Tables: Proposed Paper 2
Table 1 Summary of zirconium alloys analysed ............................................................................. 135
List of Tables: Proposed Paper 3
Table 1 Material Properties for the zirconium alloy substrate and oxide film ................................. 160
List of Tables: Proposed Paper 4
Table 1 Showing the effect of surface profile on the calculations for oxide thickness (µm) ........... 180
Table 2 Surface/Interface Roughness Rq (µm) .............................................................................. 180
Table 3 Oxide Crack Area and Density .......................................................................................... 180
List of Tables: Proposed Paper 5
Table 1 Material Properties used in finite element analysis ........................................................... 204
Table 2 Lattice constants used to define the phase transformation ............................................... 204

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List of Figures: Thesis
Figure 1 Shares of electricity generation based on energy source for the second quarter of 2013 in
the UK (DECC 2013). ........................................................................................................................ 20
Figure 2 Net Energy Import Dependency for the UK (DECC 2013). ................................................ 20
Figure 3 Illustration of the hexagonal close packed lattice structure (Wang & Beyerlein 2012). ...... 26
Figure 4 Schematic illustration of the transition points in the oxidation kinetics of zirconium alloys.
.......................................................................................................................................................... 28
Figure 5 Carbon replica image showing the predominantly columnar monoclinic structure for oxide
formed on Zr after 24hr oxidation in air (Cox 2005). ......................................................................... 31
Figure 6 Elements of the Eshelby sequence applied to the oxidation of a rough surface (Evans et
al. 1983). ........................................................................................................................................... 56
Figure 7 Points A, B and C can be used to define the radius of curvature for point D (IntMath.com
2013). ................................................................................................................................................ 57
Figure 8 Zircaloy-4 oxidised at 360°C in primary water for (a) 3 days (b) 80 days (c) 100 days (d)
160 days of corrosion (Ly et al. 2011). .............................................................................................. 59
Figure 9 Thick cracked oxide formed above roughness peaks said to develop due to plastic
deformation of the MCrAlY Substrate (Busso et al. 2010). ............................................................... 60
Figure 10 Chart showing the dependence of the tetragonal to monoclinic phase transformation on
the change in strain energy, chemical energy and surface/interface energy (Kelly & Rose 2002). . 63
Figure 11 Illustration showing the volumetric expansion and shape change associated with the
tetragonal to martensitic phase transformation (Kelly & Rose 2002)................................................ 67
Figure 12 Schematic of X-Ray diffraction and the Bragg angle. ....................................................... 71
Figure 13 Illustration of the booster ring, storage ring and beam-lines typically associated with a
synchrotron x-ray facility. (A) electrons accelerated in inner booster ring, (B) electron released in
outer storage ring, (C) forcing electrons into a curved trajectory causes high energy X-ray emission.
.......................................................................................................................................................... 72
Figure 14 Illustration of the experimental setup in the EDDI materials science beam-line at the
BESSY II synchrotron facility in Berlin, Germany. ............................................................................ 73
Figure 15 Backscattered Scanning Electron Microscope image for the metal-oxide interface region
for artificially roughened Zircaloy-4 oxidised in steam at 400°C for 111days. .................................. 74
Figure 16 Data smoothing for the extracted metal-oxide interface of Zircaloy-4 oxidised for 74days
at 360°C in primary water.................................................................................................................. 75
Figure 17 Part representing a full coupon that could be removed from an autoclave. ..................... 77
Figure 18 2D Section of a coupon demonstrating how sections can be removed with the application
of appropriate boundary conditions and constraint equations to reduce the size of the model. ....... 77
Figure 19 Illustration of the top surface of the simulation partitioned in 21 layers that will be used to
define the oxidation process. ............................................................................................................ 78
Figure 20 Schematic for the axisymmetric simulation of a single undulation showing the definition of
the amplitude and the width. ............................................................................................................. 80
Figure 21 Schematic for the 3D quartered simulation of a single undulation. .................................. 80
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Figure 22 Model Illustration (A) and schematic showing boundary conditions (B). .......................... 82
Figure 23 Illustration of the (100) monoclinic twin plane for the V1, V2 and V3 variants. ................ 84
Figure 24 Some of the 2D first and second order finite elements available in Abaqus. ................... 85
Figure 25 Demonstrate hour-glassing in a 2D element containing four nodes and only one
integration point. ............................................................................................................................... 85
List of Figures: Proposed Paper 1
Figure 1 Oxidation kinetics (a) and hydrogen concentrations (b) for samples of Zircaloy-4 tested in
360°C simulated primary water, with the shaded green area identifying transition in the corrosion
kinetics [5]. In addition to the experimental data, the model oxidation kinetics and predicted
hydrogen pick-up are also included. ............................................................................................... 108
Figure 2 Illustration of the in-situ S-XRD experimental setup ......................................................... 108
Figure 3 Thermal profiles from the heating stage and thermocouple, and the predicted thermal
profile based on oxidation tests for Test A (top) and Test B (bottom) ............................................ 109
Figure 4 Zircaloy-4 air furnace oxidation results based on the thermal profiles for Test A (top) and
Test B (bottom) ............................................................................................................................... 109
Figure 5 ZIRLOTM air furnace oxidation results based on the thermal profiles for Test A (top) and
Test B (bottom) ............................................................................................................................... 110
Figure 6 Illustration of the Abaqus model used with layers to define oxidation of samples ........... 110
Figure 7 Zircaloy-4 oxidised at 360°C in-autoclave, showing tetragonal phase fraction (top) and
monoclinic, tetragonal, and averaged in-plane oxide biaxial compressive stresses as well as
predicted stresses (bottom), with the shaded green area identifying transition in the corrosion
kinetics [5] ....................................................................................................................................... 111
Figure 8 Example diffraction patterns for a sample of Zirclaoy-4 oxidised in-situ up-to 710°C (Test
A) .................................................................................................................................................... 111
Figure 9 Integrated intensity of monoclinic and tetragonal peaks recorded for oxides formed on
Zircaloy-4 and ZIRLOTM up to 710°C (Test A, top) and 650°C (Test B, bottom) ............................ 112
Figure 10 Zircaloy-4 oxidised up to 710°C (Test A), showing tetragonal phase fraction (top) and
measured monoclinic, tetragonal, averaged, and predicted in-plane oxide bi-axial compressive
stresses ........................................................................................................................................... 112
Figure 11 Zircaloy-4 oxidised up to 650°C (Test B), showing tetragonal phase fraction (top) and
measured monoclinic, tetragonal, averaged, and predicted in-plane oxide bi-axial compressive
stresses ........................................................................................................................................... 113
Figure 12 ZIRLOTM oxidised up to 710°C (Test A), showing tetragonal phase fraction (top) and
measured monoclinic, tetragonal, averaged, and predicted in-plane oxide bi-axial compressive
stresses (bottom) ............................................................................................................................ 113
Figure 13 ZIRLOTM oxidised up to 650°C (Test B), showing tetragonal phase fraction (top) and
measured monoclinic, tetragonal, averaged, and predicted in-plane oxide bi-axial compressive
stresses (bottom) ............................................................................................................................ 114
Figure 14 Diffraction pattern for an oxidised ZIRLOTM sample demonstrating a weak β-Zr peak in
the near surface metal substrate (B) which is not present at room temperature (A)...................... 114
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Figure 15 Stress profiles through the oxide thickness predicted by the finite element analysis ..... 115
Figure 16 Shifting average through oxide stress distribution comparing SXRD and FEA based on
input Set 1 ....................................................................................................................................... 115
Figure 17 Metal substrate creep strain predicted by finite element analysis for Zircaloy-4 oxidised at
360°C in-autoclave .......................................................................................................................... 116
List of Figures: Proposed Paper 2
Figure 1 Zircaloy-4, ZIRLOTM and A-0.0Sn oxidation kinetics in 360°C primary water, with the light
green bars representing the intervals of time in which transition appears to have occurred. ......... 136
Figure 2 Image analysis used for metal-oxide interface definition. ................................................. 136
Figure 3 Definition of the first order undulations by fitting a fourth order polynomial. .................... 137
Figure 4 Data smoothing of the second order undulations using a spline method to remove
pixellation. ....................................................................................................................................... 137
Figure 5 SEM cross section images (16000x mag.) of Zircaloy-4 samples after 54 days, 160 days
and 200 days oxidation respectively. .............................................................................................. 138
Figure 6 SEM cross section images (16000x mag.) of ZIRLOTM samples after 80 days, 140 days,
and 160 days oxidation. .................................................................................................................. 139
Figure 7 SEM cross section images (16000x mag.) of A-0.0Sn 80 days, 140 days and 160 days
oxidation. ......................................................................................................................................... 140
Figure 8 FFT output comparing an idealised interface and that taken for Zircaloy-4 after 74days.
........................................................................................................................................................ 141
Figure 9 Changes in the Root Mean Squared of the interface height. ........................................... 141
Figure 10 Change in interface roughness based on the profile slope (Rdq) during oxidation. ....... 142
Figure 11 Histogram (Range=6) for the radius of curvature of a metal-oxide interface on Zircaloy-4
after 74days oxidation. Median and Mean based on the full distribution. ....................................... 142
Figure 12 Median radius of curvature during oxidation. .................................................................. 143
Figure 13 Comparison of the stored elastic energies in oxides formed on ZIRLOTM, A-0.6Sn, and
A-0.0Sn for different oxide exposure times in 360°C simulated primary water [33]. ...................... 143
List of Figures: Proposed Paper 3
Figure 1 Schematic for the axisymmetric simulation of a single undulation showing the definition of
the amplitude and the width. ........................................................................................................... 161
Figure 2 Schematic for the 3D quartered simulation of a single undulation from two angles.
Symmetry boundary conditions are applied to faces A and B. Linear constraint equations are
applied to faces C and D. ................................................................................................................ 161
Figure 3 Change in the undulation amplitude for different initial undulation amplitudes as a result of
deformation for the 3D quartered simulation using anisotropic material properties. ...................... 162
Figure 4 Comparison of the maximum principal stress in the oxide layer for different undulation
amplitudes taken for linear elastic simulations................................................................................ 162
Figure 5 Comparison of the maximum principal stress in the oxide layer for different undulation
amplitudes taken for elastic-plastic simulations. ............................................................................. 163
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Figure 6 Stress distributions showing the maximum principal stresses for elements within the oxide
layer taken from a fully elastic 3D simulation. The arrows illustrate the triaxial tensile stress state
above the peak. .............................................................................................................................. 163
Figure 7 Distribution of plastic strain in the 3 or Z direction for the metal substrate for an elastic–
plastic 3D simulation. ...................................................................................................................... 164
Figure 8 Stress distributions showing the maximum principal stresses for elements within the oxide
layer for an elastic-plastic 3D simulation. The arrows illustrate the in-plane biaxial compressive
stress and out-of-plane tensile stress. ............................................................................................ 164
Figure 9 Maximum principal stress in the oxide layer for elastic-plastic simulations with different
undulation amplitudes and yield strengths in the metal substrate. The green shaded area
represents known fracture strengths for manufactured zirconia [27–29]. ...................................... 165
Figure 10 Maximum principal stress in the oxide layer for an elastic model with an undulation
amplitude of 0.1µm, assessing the impact of the different components of the anisotropic strain
tensor. ............................................................................................................................................. 165
Figure 11 Through oxide stress distributions from the undulation peak at the metal-oxide interface
to the oxide surface. Comparing S11=S22 (in-plane stress) with S33 (out-of-plane stress), for
different levels of in-plane expansion. ............................................................................................ 166
Figure 12 Maximum principal stress in the oxide layer for different undulation amplitudes using an
elastic model and an isotropic oxidation expansion strain tensor. The green shaded area
represents known fracture strengths for manufactured zirconia [27–29]. ...................................... 166
Figure 13 Distribution of plastic strain in the 3 or Z direction in the metal substrate for different
undulation amplitudes using an elastic model and an isotropic oxidation expansion strain tensor.
........................................................................................................................................................ 167
Figure 14 Maximum principal stress in the oxide layer for different undulation amplitudes and
substrate yield strengths using an elastic-plastic model and an isotropic oxidation expansion strain
tensor .............................................................................................................................................. 167
List of Figures: Proposed Paper 4
Figure 1 SEM Image for Zircaloy-4 artificially roughened with P80 grit paper and oxidised in 400°C
steam .............................................................................................................................................. 181
Figure 2 Example of how fitting a spline can smooth the data and remove the effect of pixellation
........................................................................................................................................................ 181
Figure 3 Definition of the form present within the spline profile ...................................................... 182
Figure 4 Definition of the roughness present within the primary profile ......................................... 182
Figure 5 the oxidation kinetics for Zircaloy-4 with different surface preparation oxidised in 400°C
steam .............................................................................................................................................. 183
Figure 6 SEM backscattered cross-section images of metal-oxide region for samples of Zircaloy-4
after the stress relief anneal taken at 2000x magnification ............................................................ 184
Figure 7 SEM backscattered cross-section images of metal-oxide region for samples of Zircaloy-4
after 111days oxidation in 400°C steam taken at 2000x magnification .......................................... 185
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