The influence of alloying elements on the corrosion of Zr alloys

Bell, B.D.C.; Murphy, Samuel T.; Burr, Patrick A.; Comstock, R. J.; Partezana, Jonna M.; Grimes, Robin W.; Wenman, M.R.

doi:10.1016/j.corsci.2015.12.022

Cited by 46 publications

(24 citation statements)

References 38 publications

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“…The The elevated temperature of 1500 K was used for the tetragonal phase simulations to account for the lack of stress stabilisation in the simulations, which is present in the oxide layer. In this we follow an approach used previously [45,11,22,46], however concern remains that the intrinsic defect concentration predicted in these high temperature diagrams may be exces- . At high temperature, the isolated defect behaviour (Figure 5b) shows that Cluster Energy (eV) Spin The presence of the unpaired electrons in the {Nb Zr :…”

Section: Resultsmentioning

confidence: 99%

The effect of Nb on the corrosion and hydrogen pick-up of Zr alloys

et al. 2017

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Zr-Nb alloys are known to perform better in corrosion and hydrogen pick-up than other Zr alloys but the mechanism by which this happens is not well understood. Atomistic simulations using density functional theory of both tetragonal and monoclinic ZrO2 were performed, with intrinsic defects and Nb dopants. The overall defect populations with respect to oxygen partial pressure were calculated and presented in the form of Brouwer diagrams. Nb is found to favour 5 + in monoclinic ZrO2 at all partial pressures, but can exist in oxidation states ranging from 5 + to 3 + in the tetragonal phase. Nb5+ is charge balanced by Zr vacancies in both phases, suggesting that contrary to previous assumptions, Nb does not act as an n-type dopant in the oxide layer. Clusters containing oxygen vacancies were considered, Nb2+ was shown to exist in the tetragonal phase with a binding energy of 2.4 eV. This supports the proposed mechanism whereby low oxidation state Nb ions (2 + or 3+) charge balance the build-up of positive space-charge in the oxide layer, increasing oxygen vacancy and electron mobility, leading to near-parabolic corrosion kinetics and a reduced hydrogen pick-up. Previous experimental work has shown that tetragonal ZrO2 transforms to the monoclinic phase during transition, and that during transition a sharp drop in the instantaneous hydrogen pick-up fraction occurs. The oxidation of lower charge state Nb defects to Nb5+ during this phase change, and the consequent temporary n-doping of the oxide layer, is proposed as an explanation for the drop in hydrogen pick-up during transition

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Section: Resultsmentioning

confidence: 99%

The effect of Nb on the corrosion and hydrogen pick-up of Zr alloys

et al. 2017

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“…This change in oxidation state of the Sn cations, and the associated drop in the oxygen vacancy concentration, destabilised the tetragonal phase and led to its transformation to the monoclinic phase and this in turn could have initiated cracking in the oxide associated with the transition because of the 4% volume increase from the tetragonal to monoclinic phases. The issue with this initial theory is it did not explain why the corrosion rate does not increase with increased oxygen vacancy concentration -something that was observed by Bell et al when Zr is doped with Sc 3+ ions [10].…”

Section: Introductionmentioning

confidence: 95%

“…In this paper a set of defects are modelled in tetragonal ZrO 2 using the same technique employed by Bell et al [8,10,11]. These defects are bound DFT simulations were performed using the CASTEP 8.0 software [12], with ultra-soft pseudo potentials and a cut-off energy of 550 eV.…”

Section: Introductionmentioning

confidence: 99%

The effect of Sn–VO defect clustering on Zr alloy corrosion

et al. 2018

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Density functional theory simulations were used to study Sn defect clusters in the oxide layer of Zr-alloys. Clustering was shown to play a key role in the accommodation of Sn in ZrO 2 , with the {Sn Zr :V O } × bound defect cluster dominant at all oxygen partial pressures below 10-20 atm, above which Sn Zr × is preferred. {Sn Zr :V O } × is predicted to increase the tetragonal phase fraction in the oxide layer, due to the elevated oxygen vacancy concentration. As corrosion progresses, the transition to Sn Zr × , and resultant destabilisation of the tetragonal phase, is proposed as a possible explanation for the early first transition observed in Sn-containing Zr-Nb alloys.

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“…In the past decades, Zircaloy has been widely applied as fuel cladding material due to its low thermal neutron absorption cross‐section, excellent mechanical properties, and good corrosion resistance under normal pressure water reactor (PWR) operating condition (360 °C, 18.6 MPa cooling water) . However, these satisfactory performances of Zircaloy are challenged when a loss of coolant accident (LOCA) occurs.…”

Section: Introductionmentioning

confidence: 99%

Steam oxidation resistance of plasma sprayed chromium‐containing coatings at 1200 °C

Zhao

Niu

Xue

et al. 2018

Materials & Corrosion

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In order to improve the high‐temperature steam oxidation resistance of Zircaloy fuel claddings, chromium‐containing coatings (Cr3C2‐NiCr and NiCr) were deposited on a Zr‐4 substrate by air plasma spray. The steam oxidation resistance of the two coatings was evaluated at 1200 °C under atmospheric pressure. The weight changes, phase compositions, and microstructures of the coatings before and after the oxidation test of 1 h were characterized. Results revealed that the Cr3C2‐NiCr coating effectively protected Zr‐4 from oxidation. A protective Cr2O3 scale with a thickness of about 7 µm was formed on the surface of the Cr3C2‐NiCr coating after 1 h duration and the formed oxide layer was about 100 times thinner than that formed on the uncoated sample. A none protective oxide scale was formed on the surface of the NiCr coated Zr‐4 samples. Severe inter‐diffusion between the NiCr coating and the Zr‐4 substrate was observed. The oxidation mechanisms of the two types of chromium‐containing coatings were analyzed and compared in detail.

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The influence of alloying elements on the corrosion of Zr alloys

Cited by 46 publications

References 38 publications

The effect of Nb on the corrosion and hydrogen pick-up of Zr alloys

The effect of Nb on the corrosion and hydrogen pick-up of Zr alloys

The effect of Sn–VO defect clustering on Zr alloy corrosion

Steam oxidation resistance of plasma sprayed chromium‐containing coatings at 1200 °C

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