Possible origin and roles of nano-porosity in ZrO 2 scales for hydrogen pick-up in Zr alloys

Lindgren, Mikaela; Geers, Christine; Panas, Itai

doi:10.1016/j.jnucmat.2017.05.017

Cited by 14 publications

(8 citation statements)

References 17 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…All these factors depend on the oxidation temperature and time, composition and fugacity of a medium, and chemical and phase composition of an alloy [23]. The obtained results here correspond to the previous reports regarding the temperature dependence of the oxide layer growth [25,[61][62][63][64][65][66][67], the complex multilayer and multiphase structure [68][69][70][71], growth of the oxide layer in columnar grains [68,72], and the appearance of porosity [25,33,[73][74][75] and cracks [76][77][78][79]. Interestingly, it was also noted that a severe descaling of the oxide layer appeared in these investigations at a relatively high temperature.…”

Section: Characteristics Of Oxide Layerssupporting

confidence: 88%

Hydrogen Embrittlement and Oxide Layer Effect in the Cathodically Charged Zircaloy-2

et al. 2020

View full text Add to dashboard Cite

The present paper is aimed at determining the less investigated effects of hydrogen uptake on the microstructure and the mechanical behavior of the oxidized Zircaloy-2 alloy. The specimens were oxidized and charged with hydrogen. The different oxidation temperatures and cathodic current densities were applied. The scanning electron microscopy, X-ray electron diffraction spectroscopy, hydrogen absorption assessment, tensile, and nanoindentation tests were performed. At low oxidation temperatures, an appearance of numerous hydrides and cracks, and a slight change of mechanical properties were noticed. At high-temperature oxidation, the oxide layer prevented the hydrogen deterioration of the alloy. For nonoxidized samples, charged at different current density, nanoindentation tests showed that both hardness and Young’s modulus revealed the minims at specific current value and the stepwise decrease in hardness during hydrogen desorption. The obtained results are explained by the barrier effect of the oxide layer against hydrogen uptake, softening due to the interaction of hydrogen and dislocations nucleated by indentation test, and hardening caused by the decomposition of hydrides. The last phenomena may appear together and result in hydrogen embrittlement in forms of simultaneous hydrogen-enhanced localized plasticity and delayed hydride cracking.

show abstract

Section: Characteristics Of Oxide Layerssupporting

confidence: 88%

Hydrogen Embrittlement and Oxide Layer Effect in the Cathodically Charged Zircaloy-2

et al. 2020

View full text Add to dashboard Cite

show abstract

“…Here we should distinguish between the preferential diffusion paths for hydrogenic species offered by grain boundaries in the nano-crystalline oxide layers [8,9,18,19] and the porosity described here. The nano-pores nucleate preferentially, but not exclusively, on oxide grain boundaries, and are often seen to align along grain boundary planes to form the nano-pipes, Fig.…”

Section: Discussionmentioning

confidence: 99%

“…There has been a good deal of focus on the concept that H transport through the oxide occurs preferentially along grain boundaries. Extensive computational studies by Panas and coworkers [18,19 and references therein] have provided detailed insight into the role of oxygen vacancies and alloying elements at grain boundaries in the oxidation of zirconium. Recently, these authors have demonstrated evidence for the possible alignment of oxygen vacancies in tetragonal ZrO2, causing a "nano-pore mediated HPU-avalanche".…”

Section: Introductionmentioning

confidence: 99%

Hydrogen pickup during oxidation in aqueous environments: The role of nano-pores and nano-pipes in zirconium oxide films

Liu

Lozano-Pérez

et al. 2019

Acta Materialia

View full text Add to dashboard Cite

Oxidation of metals by water generates hydrogen which can enter the solid causing serious degradation of its mechanical properties and may also influence the corrosion rate. The present work focuses on hydrogen pickup during the corrosion of zirconium alloys in an aqueous environment. Transmission electron microscopy using Fresnel imaging on three different samples of oxidized Zr has been used to study the type, distribution, concentration and connectivity of nano-porosity as a function of depth through the oxide layer. Extensive interconnected nano-pipes are found in the non-protective outer part of the oxide, while in the protective barrier layer closer to the metal-oxide interface, continuous nano-pipes turn into individual nano-pores. Ab initio calculations show that molecular hydrogen is formed spontaneously by the reaction of water with oxygen vacancies in zirconium oxide. Molecular dynamics simulations reveal that these H2 molecules can diffuse rapidly through nano-pores and nano-pipes as small as 0.5 nm in the oxide layer. Calculations demonstrate that molecular hydrogen dissociates spontaneously on surfaces of suboxides found experimentally at the metal-oxide interface. Oxygen vacancies in ZrO enable the ingress and diffusion of H atoms with an energy barrier of approximately 65 kJ/mol. Further diffusion of hydrogen through oxygen-saturated α-Zr metal is fast, leading to the formation of thermodynamically stable zirconium hydrides. Thus, formation and diffusion of molecular hydrogen through nano-pores in the bulk oxide and ingress of H atoms via suboxides is a possible mechanism of hydrogen pickup in any metal or alloy covered by an oxide scale that contains nano-porosity.

show abstract

“…Yet, it should be born in mind that, inasmuch as both grains coarsening models display late subparabolic scale growth, in the absence of scale breakdown the parabolic lattice diffusion channel is expected to eventually prevail. Having said this, scavenging processes driven by residual (electro-)chemical potential gradients might disallow this limit to be reached (compare, for example, the cyclic barrier oxide breakdown prevalent for zirconia formers [30,31]).…”

Section: Discussionmentioning

confidence: 99%

Impact of Grain Boundary Density on Oxide Scaling Revisited

Geers

Panas

2018

Oxid Met

Self Cite

View full text Add to dashboard Cite

A straightforward conceptual tool for discriminating between different oxide scaling processes deviating from the parabolic standard model is formulated. Grain boundary diffusion-controlled oxide scaling is generalized to include lateral grains coarsening. Building on traditional Wagner theory, attenuation of rates of inwards growing oxides owing to the gradual loss of grain boundary density is revisited. Two viable cases are identified. One has the rate of grain boundary density loss to be independent of the rate of oxide growth, while the second case takes the two instantaneous rates to be equal. Simple parabolic-logarithmic and superparabolic-cubic expressions are arrived at for the two cases, respectively. Usefulness is demonstrated by applying the models to published experimental data from 1990 to date. Upon arrival at the superparabolic-cubic behaviour, a generic mathematical form analogous to a 'spring force' attenuating the scale growth was identified. 'Parabolic', 'cubic' and 'logarithmic' scaling emerges as limiting cases.

show abstract

Possible origin and roles of nano-porosity in ZrO 2 scales for hydrogen pick-up in Zr alloys

Cited by 14 publications

References 17 publications

Hydrogen Embrittlement and Oxide Layer Effect in the Cathodically Charged Zircaloy-2

Hydrogen Embrittlement and Oxide Layer Effect in the Cathodically Charged Zircaloy-2

Hydrogen pickup during oxidation in aqueous environments: The role of nano-pores and nano-pipes in zirconium oxide films

Impact of Grain Boundary Density on Oxide Scaling Revisited

Contact Info

Product

Resources

About