Fundamental understanding of Nb effect on corrosion mechanisms of Zr-Nb alloys in and out of reactor Zefeng ng Yu Yu 1 , Michael Moorehead 2 , Leo Borrel 2 , Mukesh Bachhav 3 , Lingfeng He 3 , Jing Hu 4 and Adrien en Couet 1,2 1 University of Wisconsin, Madison – Material Science and Engineering Department 2 University of Wisconsin, Madison – Engineering Physics Department 3 Idaho National Laboratory – Materials and Fuels Complex 4 Argonne National Laboratory – Intermediate Voltage Electron Microscopy-T andem Facility UW Environmental Degradation of Nuclear Materials Laboratory 19 th International Symposium on Zirconium in the Nuclear Industry
R ESEARCH EARCH B ACKGRO AND M OTIV ROUN UND AN IVATIO TION • Irradiation effect on microstructure of ZrNb alloy: • In-reactor irradiation induces “βNb” platelets [2] . • Proton irradiation also induces the precipitation of those platelets [3] . • Hy Hypo pothe thesis sis: Irradi radiat atio ion reduc educes es Nb Nb conc concent entrat atio ion in in α -Zr Zr matri atrix by by pr precipit cipitat atin ing Nb Nb-rich rich ir irra radi diat atio ion-in indu duced ced pl plat atel elet ets resulting esulting in in low lower er corrosi osion on kinet etics ics neutron irradiated M5 1 dpa proton irradiated M5 14 dpa [2] Doriot, S, et al. ASTM Special Technical Publication , vol. 1543, 2015, pp. 759–799. [3] Verlet, Romain. Influence of Irradiation and Radiolysis on the Corrosion Rate and Mechanisms of Zirconium Alloys , 2015. UW Environme onment ntal Degr gradat dation on of Nuclea ear Mater erial als s Laborato oratory 2 19 th International Symposium on Zirconium in the Nuclear Industry
1. Nb distribution and electronic structure in the oxide U NIRRA TED Z R -1.0N 0N B M ODEL A LL RRADIA DIATE LLOY ZrNb Microchemistry Effect on Corrosion Kinetics: Understand how Nb distribution affect corrosion kinetics of Zr alloys. • Samples: • 720 ͦC Zr-1.0Nb: αZr + βZr (Fe = 750 ppm) • 580 ͦC Zr-1.0Nb: αZr + βNb + Laves phases (Fe = 600 ppm) Expe pected ted microst ostruct ructur ures es: 720 ͦC 580 ͦC 720 ͦC 580 ͦC UW Environme onment ntal Degr gradat dation on of Nuclea ear Mater erial als s Laborato oratory 3 19 th International Symposium on Zirconium in the Nuclear Industry
1. Nb distribution and electronic structure in the oxide C ORR SION K INETICS OF Z R -1.0N 0N B RROSIO ETICS OF 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…) UW Environmental Degradation of Nuclear Materials Laboratory 4 19 th International Symposium on Zirconium in the Nuclear Industry
1. Nb distributio ribution n and electronic tronic struc ructu ture e in the ox oxid ide U NIRRA TED Z R -1.0N 0N B C HA RRADIA DIATE HARA RACT CTERI RIZA ZATION ION • 720 ͦC Zr-1.0Nb: • 580 ͦC Zr-1.0Nb: αZr + βZr (highlighted in yellow) aZr + βNb (highlighted in red ) βZr BF HAADF β Nb remai ains ns in 45 days 7 days Nb in βZr After corrosion Thickness: oxide, , limit ited ed Nb Thickness: dissolves in oxide 360 °C, 18 MPa 1.8 μm 0.86 μm dissolut lutio ion [5] M. Moorehead, Z. Yu, L. Borrel, Z. Couet, J. Hu, Z. Cai, Comprehensive Investigation of the UW Environme onment ntal Degr gradat dation on of Nuclea ear Mater erial als s Laborato oratory 5 Role of Nb on the Oxidation Kinetics of Zr-Nb Alloys, Corrosion Science (2019). 19 th International Symposium on Zirconium in the Nuclear Industry
1. Nb distribution and electronic structure in the oxide U NIRRA TED Z R -1.0N 0N B C HA RRADIA DIATE HARA RACT CTERI RIZA ZATION ION • Microchemistry of βZr at oxide and metal interface : metal oxide • Nb Nb is is seen to to leech out fr from the β -Zr Zr precipit itat ate upo pon oxid idation tion. • Doping ping the oxide de with additional ditional Nb Nb in in soli lid solut ution ion • WHAT IS IS THE Nb Nb OXID IDATIO TION ST STATE? E? [5] M. Moorehead, Z. Yu, L. Borrel, Z. Couet, J. Hu, Z. Cai, Comprehensive Investigation of the UW Environmental Degradation of Nuclear Materials Laboratory 6 19 th International Symposium on Zirconium in the Nuclear Industry Role of Nb on the Oxidation Kinetics of Zr-Nb Alloys, Corrosion Science (2019).
1. Nb distribution and electronic structure in the oxide XANES S ETU P A T TH E S YN C H ROTRO N APS Monochromatic X-Ray Beam Nb K α X-Ray X-Ray Detector XANES Sample Fitting Raw Data Data Fit 1.4 NbO Powder, 2+ Nb Alloy, Metallic Incident X-Ray Energy 1.2 Nb Powder, Metallic Normalized Counts 1 • Monochromatic incident X-ray beam is 0.8 increased in energy 0.6 • Shape of the Nb K α X-ray emission curve can be fit to known standards 0.4 using Athena 0.2 • Metallic/Oxidized fractions can then be determined 0 18950 19000 19050 19100 Incident X-Ray Energy (eV) UW Environme onment ntal Degr gradat dation on of Nuclea ear Mater erial als s Laborato oratory 19 th International Symposium on Zirconium in the Nuclear Industry
1. Nb distribution and electronic structure in the oxide XANES ANES D ATA A NAL ALYSIS SIS • Nb experiences delayed layed oxi xida dation tion in comparison to the Zr matrix. Oxidation Profile Zr-1.0Nb (720C) 1.2% M/O O/W Amount of Nb oxidized (wt%) 1.0% 0.8% 2 um 0.6% 0.4% 0.2% 0.0% -4 -2 0 2 4 Distance from interface UW Environme onment ntal Degr gradat dation on of Nuclea ear Mater erial als s Laborato oratory 8 19 th International Symposium on Zirconium in the Nuclear Industry
1. Nb distribution and electronic structure in the oxide XANES R ESU LTS Zr-1.0Nb (720°C) • 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? UW Environme onment ntal Degr gradat dation on of Nuclea ear Mater erial als s Laborato oratory 9 19 th International Symposium on Zirconium in the Nuclear Industry
1. Nb distribution and electronic structure in the oxide M O D ELIN G O F N B EFFEC T O N C O RRO SIO N • Rationalization using the Coupled Current Charge Compensation model: 𝜖𝐾 𝑡 𝑦,𝑢 𝜖𝐷 𝑡 𝑦,𝑢 .. and 𝑓 − : • 1D conservation law for V O + = 0 𝜖𝑦 𝜖𝑢 • 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. diffusing species − 𝑓𝜂 𝑡 𝑎 𝑡 𝑓𝑏𝐹 𝑙 − 𝑎 𝑡 𝑓𝑏𝐹 𝑙 𝑙−1 e 𝑙 e 𝑙 𝐶 𝑈 𝑙 𝐶 𝑈 𝑙 𝐶 𝑈 𝑎 𝑡 𝑓𝐾 𝑡 = 0, 𝐾 𝑡 = 2𝑏𝜉 𝑡 e 𝐷 𝑡 − 𝐷 𝑡 2 um 𝑡 • Local space charge at monolayer 𝑙 (hydrogen not modeled, see poster session): All Aliovalent species ions 𝑙 − 𝐷 e − 𝑙 + 𝑙 = 2𝐷 V O 𝑙 𝜍 𝑙 = 𝑎 𝑡 𝐷 𝑡 𝑎 𝑗 𝐷 𝑗 .. 𝑡 𝑗 UW Environme onment ntal Degr gradat dation on of Nuclea ear Mater erial als s Laborato oratory 10 19 th International Symposium on Zirconium in the Nuclear Industry
1. Nb distributio ribution n and electronic tronic struc ructu ture e in the ox oxid ide M O D ELIN G O F N B EFFEC T O N C O RRO SIO N • Space charge 𝝇 𝒚 → local field, 𝐹 𝑙 : l ele electric ic fie 𝑙 𝐹 𝑙 = 𝐹 0 + 8𝜌𝑏𝑓 𝑚 𝑚 Γ 𝑙 2𝐷 V O − 𝐷 e − .. 𝜁𝜁 0 𝑚=1 𝑙 σ 𝑛=0 𝑚 5 4 − 𝑛 𝐷 Nb 4−m ′ with Γ 𝑙 = 1 − 𝑚 𝑚 2𝐷 V O − 𝐷 e − .. 𝑚=1 • Γ 𝑙 is defined as the space charge compensation factor evaluated at the 𝑙 th 2 um layer. 𝑚 , then loca 𝑚 5 𝑚 • If Γ 𝑙 = 0 ⟺ σ 𝑛=0 4 − 𝑛 𝐷 Nb 4−m ′ = 2𝐷 V O − 𝐷 e − cal l .. el electroneutrali lity is achieved thanks to the solute Nb in the oxide • If Γ 𝑙 = 0 ⟹ para raboli lic kinetics • Solved using a robust Newton-Raphson method. UW Environme onment ntal Degr gradat dation on of Nuclea ear Mater erial als s Laborato oratory 11 19 th International Symposium on Zirconium in the Nuclear Industry
1. Nb distribution and electronic structure in the oxide M ODE OF N B EFF ON C ORROS DELING LING OF FFECT ECT ON ROSIO ION • C4 model result: As expected, the ZrNb alloy corrosion 2 um kinetics decreases (and becomes sub- parabolic) IF LESS Nb IS IN SOLID SOLUTION to compensate the space charge UW Environmental Degradation of Nuclear Materials Laboratory 12 19 th International Symposium on Zirconium in the Nuclear Industry
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