MARTENSITIC ALLOYS IN SUPERCRITICAL WATER

DETERMINATION OF OXIDATION MECHANISMS OF FERRITICMARTENSITIC ALLOYS IN SUPERCRITICAL WATER

by

Pantip Ampornrat

A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Nuclear Engineering and Radiological Sciences) in The University of Michigan 2011

Doctoral Committee: Professor Lumin Wang, Co-Chair Professor Gary S. Was, Co-Chair Professor J. Wayne Jones Assistant Research Scientist Kai Sun

©

Pantip Ampornrat All Rights Reserved

2011

To my parents and grandparents

ii

ACKNOWLEDGEMENT

I would like to thank my advisor Dr. Gary S. Was and co-advisor Dr. Lumin Wang, for their guidance and support for entire time I worked on this thesis. I would also like to thank the members of my dissertation committee, Dr. Wayne Jones and Dr. Kai Sun for their helpful insight as I completed this thesis. I would also like to thank my colleagues and friends, Elaine West, Deepak Kumar, Gaurav Gupta, Micah Hackett, Josh McKinley, Anne Campbell, Michael McMurtrey, Cheng Xu, Gokce Gulsoy, Kale Stephenson, Tyler Moss, Janelle Wharry, Efrain Hernandez-Rivera, Jonathan Wierschke, Weixing Li, Guang Ran, Liang Chen, Stephen Raiman, Shyam Dwaraknath, William Lai, Jan Michalicka and Jeremy Bischoff for their support and fruitful discussion. I would also like to thank research staffs who assisted me in lab and gave me very helpful suggestions, Chi Bum Bahn, Sebastien Teysseyre, Yanbin Chen, Zhijie Jiao, Alex Flick, Haiping Sun, John Mansfield and NERS staffs, Peggy Gramer, Caroline Joaquin, Cherilyn Davis, Edward Birdsall and Pam Derry. I would also like to thank my friends outside working area, Phongphaeth Pengvanich, Niravun Pavenayotin, Yimprayoon’s family, Rhatarporn Kessom, Chetwana Rungwanitchakul, Anupap Somboonsavatdee, Naruemol Sigha-Dong, Chanokruthai Choenarom, Yuko Kobayashi, Ning Ying Jeab, Bo Fai Ying, Godaiko’s staffs, The old siam’s staffs and a lot of friends who have been being with me along this journey. iii

Lastly, I would like to express my deep appreciation to my parents, grandparents and my family members for their patience, understanding and support they have given to me the entire time. I would also like to thank the Thai Government and Thailand Institute of Nuclear Technology who supported me the full scholarship for Ph.D. study. This work was supported by US Department of Energy under I-NERI project contract number 3F-01041.

iv

TABLE OF CONTENTS

DEDICATION

ii

ACKNOWLEDMENTS

iii

LIST OF FIGURES

viii

LIST OF TABLES

xxi

LIST OF APPENDICES

xxiv

ABSTRACT

xxv

CHAPTER 1. INTRODUCTION

1

2. BACKGROUND

8

2.1 Supercritical Water 2.2 Ferritic-martensitic Alloys 2.2.1 Development and Composition Design 2.2.2 Phase Constitution 2.2.3 Microstructure of F-M Alloys 2.3 Oxidation of Ferritic-martensitic Alloys in SCW Environment 2.3.1 Overview of Oxidation of F-M alloys 2.3.1a Fundamental of Oxidation 2.3.1b Oxidation Rate 2.3.1c Oxide Structure 2.3.2 Effects of Alloy Composition and Microstructure 2.3.2a Chromium Content 2.3.2b Minor Alloying Elements 2.3.2c Alloy Microstructure 2.3.3 Environmental Effects on Oxidation of Ferritic-martensitic Alloys 2.3.3a Oxidation in Steam 2.3.3b Oxidation in Gas 2.3.3c Oxidation in SCW 2.4 Conclusion v

9 15 15 21 24 27 27 27 31 34 35 35 39 41 42 43 46 47 53

2.5 Objective, Significant of Study and Approaches 3. EXPERIMENT

53 94

3.1 Alloy Composition and Process Condition 3.2 Sample Preparation for Exposure Experiments 3.3 Supercritical Water Test Facilities 3.4 Exposure Experiments and Test Conditions 3.4.1 Sample Installation in Autoclave 3.4.2 Operation of SCW Systems 3.4.3 Water Chemistry 3.4.4 Experimental Conditions 3.5 Oxidation Rate Measurements 3.6 Sample Preparation for Characterizations 3.6.1 Cross-sectional SEM Sample Preparation 3.6.2 Cross-sectional TEM Sample Preparation by Focused Ion Beam 3.7 Microstructural Characterization 3.7.1 Scanning Electron Microscopy 3.7.2 X-ray Diffraction 3.7.3 Transmission Electron Microscopy 3.7.4 Energy Dispersive Spectroscopy 3.8 Error Analysis 4. EXPERIMENTAL RESULTS

94 96 98 103 103 103 105 106 107 108 109 109 114 114 115 117 120 124 151

4.1 Oxidation Rate 4.1.1 Time-dependence of Oxidation Rate 4.1.2 Temperature-dependence of Oxidation Rate 4.1.3 Dissolved Oxygen Effect 4.2 Surface Oxide 4.2.1 Surface Oxide Morphology 4.2.2 Surface Oxide Phase 4.2.3 XPS Analysis of Surface Oxide 4.3 Oxide Scale Structure and Composition 4.3.1 Outer Oxide 4.3.2 Inner Oxide 4.3.3 Transition Layer and Cr-enriched Oxide 4.3.4 Alloy Effect on Oxide Structure at 600°C 4.4 Microstructure of Alloy and Oxide 4.4.1 Alloy Microstructure 4.4.2 HCM12A Oxidized in 400°C Deaerated SCW 4.4.3 HCM12A Oxidized in 500°C Deaerated SCW 4.4.4 HCM12A Oxidized in 500°C SCW Containing 300 ppb DO 4.4.5 HCM12A Oxidized in 600°C Deaerated SCW 4.4.6 T91 Oxidized in 600°C Deaerated SCW 4.4.7 HT-9 Oxidized in 600°C Deaerated SCW vi

152 152 154 157 158 158 160 161 163 164 164 165 167 168 168 169 172 174 175 179 181

4.4.8 9Cr-ODS Oxidized in 600°C Deaerated SCW 5. DISCUSSION

183 293

5.1 Time and Temperature Dependence of the Weight Gain and Oxide Growth 294 5.1.1 Time Dependence of the Weight Gain and Oxide Growth 294 5.1.2 Temperature Dependence of the Weight Gain and Oxide Growth 297 5.1.3 Determination of Location of Original Alloy Substrate and Mass Balance Equation 304 5.1.4 Determination of Rate Limiting Process from Diffusion Coefficient 309 5.2 Formation of Oxide Structure 318 5.2.1 Determination of Oxygen Partial Pressure at Inner oxide-Outer oxideAlloy Interfaces 318 5.2.2 Formation of Outer Oxide 327 5.2.3 Formation of Inner Oxide 329 5.2.4 Formation of Transition Layer 337 5.3 Oxidation Mechanism 347 5.3.1 Defect Formation in Oxide 347 5.3.2 Summary of Oxidation Mechanisms 355 6. CONCLUSION

388

7. FUTURE WORK

392

vii

LIST OF FIGURES Figure 1.1

Schematic diagram of the Generation IV SCWR concept ......................................... 6

2.1 Phase diagram for water [1]. ....................................................................................... 59 2.2 (a) Variation in the density of water with temperature showing the drop in density at critical region (350-400°C) [5]. (b) Plots of density vs. temperature for SCW as a function of pressure [6]. (Note that the large filled circles indicate values for HCl solution in the SCWO.) ............................................................................................. 60 2.3 Plots of viscosity vs. temperature for SCW as a function of pressure [6]. (Note that the large filled circles indicate values for HCl solution in the SCWO.) ................... 61 2.4 (a) Plots of static dielectric constant as a function of temperature [12]...................... 62 2.5 Ionic products as functions of temperature and pressure. [5] ..................................... 63 2.6 Thermo-physical properties of SCW at pressure 25 MPa [1]. .................................... 64 2.7 The water trimer consists of three water molecules. Each water monomer acts as a single hydrogen bond donor and accepter. [21] ........................................................ 65 2.8 Development of ferritic alloys for boilers. (a) Schematic diagram shows development of F-M alloys that are classified into four generations based on alloying elements and creep strength [22]. (b) History of improvement of creep strength of F-M alloys and austenitic alloys [24]. .......................................................................................... 66 2.9 Relation between allowable metal temperature at 49 MPa of allowable stress and relative material cost [22]. ......................................................................................... 67 2.10 General concept of alloy composition design for heat resistant alloy [22]............... 68 2.11 Alloy design for HCM12A [27]................................................................................ 69 2.12 Phase diagram of Fe-C-Cr alloys showing the effect of chromium on the constitution of Fe-Cr-C alloys containing 0.1% C [23, 32]; note that (CrFe)4C is a M23C6 carbide. ................................................................................................................................... 70

viii

2.13 The Schaeffler-Schneider diagram represent the correlation between the phases present to the chromium and nickel equivalent in 9-12%Cr alloys [23]. .................. 71 2.14 Optical micrograph shows a ferrite stringer in HCM12A microstructure. [34] ....... 72 2.15 Effect of tempering temperature on hardness of a 12Cr-0.14C alloy [23, 37] ......... 73 2.16 Schematic diagram of the microstructure of normalized and tempered F-M alloys. 74 2.17 Ellingham/Richardson diagram shows plot of free energy with temperature for various oxides [50]. ................................................................................................... 75 2.18 Phase diagram of Fe-O [47]. ..................................................................................... 76 2.19 Effect of Cr addition on the corrosion rate of alloy at 1000oC [47]. ........................ 77 2.20 Schematic representation of all possible component of oxide layers on Fe-Cr alloy [47]. ........................................................................................................................... 78 2.21 Schematic diagram of oxide structure formed on 9Cr-1Mo steel exposed in air at 400-600°C [59] .......................................................................................................... 79 2.22 Oxidation of 1Cr, 10Cr, 10Cr-6.52Co and 12Cr in Ar-50%H2O at 550-650°C reported by Zurek et al. (a) Oxidation rate, (b) Composition profiles of 10Cr-6.52Co exposed at 600°C, and (c) Composition profiles of 12%Cr exposed at 625°C. Both composition profiles show enrichment of Cr at the alloy/oxide interface. [62] ........ 80 2.23 Schematic illustration of oxidation rate as function of Cr content for commercial ferritic alloys in steam with the temperature range of 550-650C. Arrows indicate qualitative changes of critical Cr-content by additions of Si, Co, and Mn respectively. [63] ....................................................................................................... 81 2.24 Effects of steam pressure: Plots of oxidation rate constants of F-M alloys HCM2S, NF616 and HCM12A versus steam pressure tested at (a) 600°C and (b) 700°C. The Arrhenius plots of kp measured at (c) 10 MPa and (d) 2 MPa or lower show changes in activation energies trend. [75] ............................................................................... 82 2.25 Effect of water vapor and steam composition: Scales formed on Fe-10Cr alloy after exposure in (a) Ar-20%O2, (b) Ar-4%H2-7%H2O, and (c) Ar-7%H2O and at 900°C for 72 hours, and (d) weight gain. [76]...................................................................... 83 2.26 Depth profiles of P91 after oxidation in N2- 1 vol%16O2- 2 vol%H218O2 at 650°C. The profile after (a) 1 h, (b) 7 h, and 30 h show 16O in the inner layers, and 18O from water molecules distribute in the outer layers. [77] .................................................. 84 2.27 Temperature effect of oxidation in dry air: (a) Double logarithmic plot of weight gain and temperature of HT-9 tested in dry air at 600-950°C. (b) The partial

ix

dissolution of grain structure in the internal selective oxidation zone. Grain boundaries are outline with Cr-rich/Fe oxide. [74] ................................................... 85 2.28 Potential-pH diagram for iron in supercritical aqueous solution at 400°C and P = 50 MPa. The diagram shows the approximate regions in potential-pH space for the operation of SCWO reactors and SCW thermal power plants. [6] ........................... 86 2.29 Oxidation rates of three alloy classes as represented by 625 (Ni-based alloy), D9 (austenitic alloy), and HCM12A (F-M alloy). The samples were tested in 500°C deaerated SCW (25 ppb O2) for 1026 hours. [88] ..................................................... 87 3.1 Scanning electron microscope image for the microstructure of T91. ..................... 134 3.2 Optical micrograph of HCM12A [5]. ...................................................................... 135 3.3 Scanning electron microscope image for HT-9. ...................................................... 136 3.4 SEM images of microstructure of 9Cr-ODS [6]. .................................................... 137 3.5 Geometry of corrosion coupon before polishing. .................................................... 138 3.6 (a) Positions of width and legth measurement of corrosion coupon. ...................... 139 3.7 Schematic diagram of the multi-sample SCW system. High pressure parts of the system are showed in highlighted. ......................................................................... 140 3.8 The multi-sample SCW system in high temperature corrosion laboratory, ............ 141 3.9 Test vessel of the multi-sample SCW system and corrosion coupons suspended inside the test vessel. .............................................................................................. 142 3.10 Plots of temperature and pressure control during an experiment at 500°C deaerated SCW for 10 hours. ................................................................................................. 143 3.11 Conductivity and DO of experiments in deaerated SCW at (a) 400°C (151 hours), (b) 500°C (182 hours), (c) 600°C (191 hours). ..................................................... 144 3.12 Conductivity and DO of experiments in 500°C SCW containing 300 ppb for 182 hours....................................................................................................................... 145 3.13 A schematic diagram of interactions of ion beam with the target material. ........... 146 3.14 Mechanical polishing steps for cross section TEM preparation; (a) a small sample was cut from the exposed corrosion coupon, (b) sample was cut into 1x2x1 mm, (c) oxide surface was protected by gluing it with M-bond™ to silicon, (d) side view of the sample glued with silicon, (e) polished top (side A) and bottom (side B) sides, (f) polished front (side C) and back (side D) sides, (g) glued on Mo TEM grid with M-bong™, (f) finished sample............................................................................... 147 x

3.15 Cross section TEM sample preparation in FIB; (a) and (b) Side and top view of sample after mechanical polishing show mechanical damages, ............................ 148 3.16 Geometries of (a) the 3° glancing angle XRD compare to (b) the standard theta2theta XRD. ........................................................................................................... 149 4.1 Plots of the time-dependence of weight gain of T91, HCM12A, HT-9, and 9Cr-ODS exposed in deaerated SCW at 400 and 500°C. (Note that the unit of oxidation rate constant from fitting equation is mg/dm2/h.) 200 4.2 Plots of the time-dependence of oxide thickness of (a) T91, (b) HCM12A and (c) HT9 exposed in deaerated SCW at 500°C. (Note that the unit of oxidation rate constant from fitting equation is µm/h.) ................................................................................ 202 4.3 Temperature-dependence of weight gain and total oxide thickness of T91, HCM12A, HT-9, and 9Cr-ODS exposed in deaerated SCW at 400, 500 and 600°C. The weight gain was normalized to 182 hours. .......................................................................... 203 4.4 Temperature-dependence of oxide layer thickness of T91, HCM12A, HT-9, 9Cr-ODS exposed in deaerated SCW at 400, 500 and 600°C. The oxide thickness was normalized to 182 hours. ......................................................................................... 204 4.5 Dissolved oxygen effect on the weight gain and total oxide thickness of T91, HCM12A, and HT-9 in 500°C SCW containing