Low temperature age hardening in U–13at.% Nb: An assessment of chemical redistribution mechanisms

Clarke, Amy J.; Field, Robert D.; Hackenberg, Robert E.; Thoma, D. J.; Brown, Donald W.; Teter, David; Miller, M.K.; Russell, K.F.; Edmonds, David; Beverini, G.

doi:10.1016/j.jnucmat.2009.06.025

Cited by 39 publications

(25 citation statements)

References 35 publications

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“…Instead, it tends to transform into different intermediate states depending on its heat treatment condition. Aging at ∼ 300 0 C and lower results in significant age-hardening accompanied by subtle microstructural changes (e.g., [1][2][3][4]). Under these conditions, the system remains distant from thermodynamic equilibrium even after long-term (∼ 5 years) aging and the specific transformation mechanisms remain unresolved.…”

Section: Introductionmentioning

confidence: 99%

Revisiting thermodynamics and kinetic diffusivities of uranium–niobium with Bayesian uncertainty analysis

Duong¹,

Hackenberg²,

Landa³

et al. 2016

Calphad

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In this work, thermodynamic and kinetic diffusivities of uranium-niobium (U-Nb) are reassessed by means of the CALPHAD (CALculation of PHAse Diagram) methodology. In order to improve the consistency and reliability of the assessments, first-principles calculations are coupled with CALPHAD. In particular, heats of formation of γ-U-Nb are estimated and verified using various density-functional theory (DFT) approaches. These thermochemistry data are then used as constraints to guide the thermodynamic optimization process in such a way that the mutualconsistency between first-principles calculations and CALPHAD assessment is satisfactory. In addition, long-term aging experiments are conducted in order to generate new phase equilibria data at the γ 2 /α + γ 2 boundary. These data are meant to verify the thermodynamic model. Assessment results are generally in good agreement with experiments and previous calculations, without showing the artifacts that were observed in previous modeling. The mutual-consistent thermodynamic description is then used to evaluate atomic mobility and diffusivity of γ-U-Nb. Finally, Bayesian analysis is conducted to evaluate the uncertainty of the thermodynamic model and its impact on the system's phase stability.

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Section: Introductionmentioning

confidence: 99%

Revisiting thermodynamics and kinetic diffusivities of uranium–niobium with Bayesian uncertainty analysis

Duong¹,

Hackenberg²,

Landa³

et al. 2016

Calphad

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show abstract

“…The combination of high spatial resolution and elemental sensitivity make APT one of the only techniques suitable to identify localized or layered hydride should it form during uranium oxidation. To date, there has been no APT investigation of the surface microstructure of uranium during the early stages of water vapour corrosion, although there have been some investigations of uranium binary alloys in the late 1980s 21 22 and limited investigations into uranium-niobium alloys using modern instruments 23 . This study aims to utilize the advances in APT instrumentation and preparation techniques over the past decade to investigate the oxide-metal interface of uranium exposed to moist air under ambient conditions and clarify the mechanism of water-driven uranium corrosion by unambiguously determining, or refuting, the presence and location of hydride within the corrosion product formed.…”

mentioning

confidence: 99%

Atomic-scale Studies of Uranium Oxidation and Corrosion by Water Vapour

Martin

Coe

Bagot

et al. 2016

Sci Rep

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Understanding the corrosion of uranium is important for its safe, long-term storage. Uranium metal corrodes rapidly in air, but the exact mechanism remains subject to debate. Atom Probe Tomography was used to investigate the surface microstructure of metallic depleted uranium specimens following polishing and exposure to moist air. A complex, corrugated metal-oxide interface was observed, with approximately 60 at.% oxygen content within the oxide. Interestingly, a very thin (~5 nm) interfacial layer of uranium hydride was observed at the oxide-metal interface. Exposure to deuterated water vapour produced an equivalent deuteride signal at the metal-oxide interface, confirming the hydride as originating via the water vapour oxidation mechanism. Hydroxide ions were detected uniformly throughout the oxide, yet showed reduced prominence at the metal interface. These results support a proposed mechanism for the oxidation of uranium in water vapour environments where the transport of hydroxyl species and the formation of hydride are key to understanding the observed behaviour.

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“…Aging at temperature greater than roughly 575 K results in significant hardening with corresponding loss of ductility and loss of corrosion resistance [8]. The hardening is due to non-lamellar precipitation at early time followed by cellular decomposition of the  toward the equilibrium phases of niobiumpoor  and niobium-rich  phase [8,9,[21][22][23][24][25] at long times. However, significant hardening is also observed after aging at temperatures as low as 475 K [23,26], but experimental determination of the mechanism of this low temperature hardening has remained elusive [23,26].…”

Section: Introductionmentioning

confidence: 99%

“…The hardening is due to non-lamellar precipitation at early time followed by cellular decomposition of the  toward the equilibrium phases of niobiumpoor  and niobium-rich  phase [8,9,[21][22][23][24][25] at long times. However, significant hardening is also observed after aging at temperatures as low as 475 K [23,26], but experimental determination of the mechanism of this low temperature hardening has remained elusive [23,26]. Using transmission electron microscopy (TEM), Hsiung interprets the microstructural evolution (at nominally 6 wt%Nb) as being consistent with spinodal decomposition after aging at 473 K for as little as 16 hours.…”

Section: Introductionmentioning

confidence: 99%

The effect of low-temperature aging on the microstructure and deformation of uranium- 6 wt% niobium: An in-situ neutron diffraction study

Brown

Bourke

Clarke

et al. 2016

Journal of Nuclear Materials

Self Cite

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The mechanical properties of uranium-niobium alloys evolve with aging at relatively low temperatures due to subtle microstructural changes. In-situ neutron diffraction measurements during aging of a monoclinic U-6Nb alloy at temperatures to 573 K were performed to monitor these changes. Further, in-situ neutron diffraction studies during deformation of U-6Nb in the as-quenched state and after aging for two and eight hours at 473 K were completed to assess the influence of microstructural evolution on mechanical properties. With heating, large anisotropic changes in lattice parameter were observed followed by relaxation with time at the aging temperature. The lattice parameters return to nearly their initial values with cooling. The active plastic deformation mechanisms including, in order of occurrence, shape-memory de-twinning, mechanical twinning, and slip-mediated deformation do not change with prior aging. However, the resistance to motion of the as-quenched martensitic twin boundaries increases following aging, resulting in the observed increase in initial yield strength.

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Low temperature age hardening in U–13at.% Nb: An assessment of chemical redistribution mechanisms

Cited by 39 publications

References 35 publications

Revisiting thermodynamics and kinetic diffusivities of uranium–niobium with Bayesian uncertainty analysis

Revisiting thermodynamics and kinetic diffusivities of uranium–niobium with Bayesian uncertainty analysis

Atomic-scale Studies of Uranium Oxidation and Corrosion by Water Vapour

The effect of low-temperature aging on the microstructure and deformation of uranium- 6 wt% niobium: An in-situ neutron diffraction study

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