Calculation of Oxygen Diffusion Coefficients in Oxide Films Formed on Low-Temperature Annealed Zr Alloys and Their Related Corrosion Behavior

Zhang, Lina; Chen, Liang Yu; Zhao, Cuihua; Liu, Yujing; Zhang, Lai-Chang

doi:10.3390/met9080850

Cited by 22 publications

(4 citation statements)

References 70 publications

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“…The thickness of the coating can substantially influence the corrosion properties of the sample to some extent. In general, a specific coating with larger thickness can exhibit lower corrosion rate due to the longer diffusion path for corrosive medium [53,54]. As mentioned earlier, the as-sprayed 50-75C coating has a larger thickness than the as-sprayed 75-100C after deposition, which is also a result of different-sized powder used.…”

Section: Electrochemical Resultsmentioning

confidence: 94%

Particle Size-Dependent Microstructure, Hardness and Electrochemical Corrosion Behavior of Atmospheric Plasma Sprayed NiCrBSi Coatings

Sang

Chen

Zhao

et al. 2019

Metals

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Particle size is a critical consideration for many powder coating-related industries since it significantly influences the properties of the produced materials. However, the effect of particle size on the characteristics of plasma sprayed NiCrBSi coatings is not well understood. This work investigates the microstructures, hardness and electrochemical corrosion behavior of plasma sprayed NiCrBSi coatings synthesized using different-sized powders. All coatings mainly consist of Ni, N 3 B, CrB, Cr 7 C 3 and Cr 3 C 2 phases. The coatings produced by small particles (50-75 µm) exhibit lower porosity (2.0 ± 0.8%). Such coatings show a higher fraction (15.5 vol.%) of the amorphous phase and lower hardness (700 HV 0.5 ) than the counterparts (8.7 vol.% and 760 HV 0.5 , respectively) produced by large particles (75-100 µm) with higher porosity (3.0 ± 1.6%). Meanwhile, the coatings produced from smaller particles possess a larger number of non-bonded boundaries, leading to the easier penetration of corrosive medium, as well as a higher corrosion current density (0.254 ± 0.062 µA/cm 2 ) and a lower charge transfer resistance (0.37 ± 0.07 MΩ cm 2 ). These distinctions are attributed to particle size-induced different melting degrees and stackings of in-flight particles during deposition. studied the effects of particle size and structure on the preferential Ce evaporation for La 2 Ce 2 O 7 particles during plasma spraying and indicated that the evaporation loss of Ce is significantly influenced by particle size, thereby affecting the properties of the as-sprayed La 2 Ce 2 O 7 coatings. Sun et al. [16] used different-sized WC powders to sinter three sets of WC-8Co cemented carbides and found that the transgranular fractures of the prepared cemented carbides are more evident with increasing WC particle size. From all this one can conclude that powder appearance potentially influences the properties and therefore the end applications of the produced products.NiCrBSi alloy coatings are also commonly prepared by metallic powder-related techniques including spraying [17,18] and laser cladding [19,20], with the aim to produce barriers to protect substrates from wear and/or corrosion. Amongst these techniques, atmospheric plasma spraying (APS) is frequently used due to its high synthesis speed and few limitations on equipment [21]. APS adopts a plasma gun as a heat source to melt the feedstock powder sprayed from the nozzle and impinges these powder particles on the substrates in a layer by layer method [22]. As a result, this processing method results in a typical lamellar microstructure in APS-prepared NiCrBSi coatings associated with a large number of pores and non-bonded boundaries (including lamellar boundaries and particle boundaries). Pores generally decrease the cohesion of the as-sprayed NiCrBSi coatings, thereby reducing their hardness and wear resistance [22]. In the meantime, non-bonded boundaries in as-sprayed NiCrBSi coatings provide diffusion paths for the ingress of corrosive species in a corrosive environment [22]. ...

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Section: Electrochemical Resultsmentioning

confidence: 94%

Particle Size-Dependent Microstructure, Hardness and Electrochemical Corrosion Behavior of Atmospheric Plasma Sprayed NiCrBSi Coatings

Sang

Chen

Zhao

et al. 2019

Metals

Self Cite

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“…The data of both corrosion potential and corrosion current density fall in the outcomes in the literature, indicating the reliability of the potentiodynamic polarization test in this work. As seen from Figure 3, when the applied anodic potential exceeds a certain value, the passivation current density keeps almost constant as the applied anodic potential increases (Qin et al, 2017;Zhang et al, 2019a;Zhang et al, 2019b). The passivation current density is nearly constant from the potential of 0 V SCE to 1.2 V SCE .…”

Section: Potentiodynamic Polarization Testmentioning

confidence: 85%

Characteristics of Passive Films Formed on As-Cast Ti–6Al-4V in Hank’s Solution Before and After Transpassivation

et al. 2021

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In this work, the characteristics of passive films formed on as-cast Ti-6Al-4V before and after transpassivation by electrochemical methods will be studied. A simulated body fluid of Hank’s solution was used as the electrolyte in this work. According to the potentiodynamic polarization test, the passivation range, transpassive range, and repassivation range of as-cast Ti-6Al-4V were obtained. Afterward, the potentiostatic polarization was employed to passivate the Ti-6Al-4V in both passivation and repassivation ranges. Electrochemical impedance spectroscopy (EIS) was used to analyze the characteristics of formed passive films. Different electrochemical behavior of as-cast Ti–6Al-4V is found in passivation and repassivation ranges. The passivation current density of the sample in the repassivation range is significantly larger than that in the passivation range. Meanwhile, the growth rate of passive film in the repassivation range is also greater than that in the passivation range. Although the sample shows a higher charge transfer impedance in the repassivation range, metastable pitting corrosion is also observed, indicating the formation of the unstable passive film. Such results advance the understanding of as-cast Ti-6Al-4V polarized under different potentials for potential biomedical applications.

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“…We determined the O concentration profile as shown in figure 14 when the temperature is 300 • C after a period of 30 years. The initial oxygen concentration at the oxide interface is approximately 27.4% atm [37], which is the terminal solubility level for O in α-Zr. As the distance from the interface increases, O concentration drops and reaches the average bulk concentration value of 0.6% atm (see figure 14).…”

Section: Implications Of the Diffusivity On Hydride Precipitationmentioning

confidence: 99%

Denuded zones in zirconium pressure vessels: oxygen’s role examined via multi-scale diffusion model

Liyanage

Miller

Rajapakse

2020

Modelling Simul. Mater. Sci. Eng.

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Zirconium alloys are extensively used as cladding material in nuclear reactors. They are vulnerable to hydrogen degradation under the harsh service conditions of the reactors. Optical micrographs taken in some pressure tubes shows the presence of hydride denuded zones closer to the surface, where the hydrides formed in this region are smaller in size compared to the bulk. We investigated the effect of oxygen on diffusivity of hydrogen in α Zr, to check the hypothesis that oxygen slows the diffusion of hydrogen and thereby encourages the occurrence of hydride denuded zones. We used a multi-scale model to simulate H diffusion in Zr with different O concentrations to identify the effect that O has on H diffusivity. From the study we found that oxygen indeed decreases the diffusivity of hydrogen in α Zr for moderate oxygen concentrations. We investigated the diffusion processes of individual H atoms, which showed that the reduction in diffusivity is caused by a decrease in the hopping rates and the formation of hydrogen traps by the combination of several interstitial sites. Though the diffusivity of H seems to be reduced by O, looking at the O concentration profiles found in Zircaloy pressure tubes, we see that the slowing down is insufficient to cause a significant enough change to the size of hydride precipitates. This causes us to reject the hypothesis as the main reason for the formation of denuded zones in Zircaloy pressure tubes.

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Calculation of Oxygen Diffusion Coefficients in Oxide Films Formed on Low-Temperature Annealed Zr Alloys and Their Related Corrosion Behavior

Cited by 22 publications

References 70 publications

Particle Size-Dependent Microstructure, Hardness and Electrochemical Corrosion Behavior of Atmospheric Plasma Sprayed NiCrBSi Coatings

Particle Size-Dependent Microstructure, Hardness and Electrochemical Corrosion Behavior of Atmospheric Plasma Sprayed NiCrBSi Coatings

Characteristics of Passive Films Formed on As-Cast Ti–6Al-4V in Hank’s Solution Before and After Transpassivation

Denuded zones in zirconium pressure vessels: oxygen’s role examined via multi-scale diffusion model

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