Preferential precipitation of hydrides in textured zircaloy-4 sheets

Kumar, Nitin; Szpunar, Jerzy A.; Zhang, He

doi:10.1016/j.jnucmat.2010.06.005

Cited by 76 publications

(24 citation statements)

References 28 publications

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“…Inverse pole figure (IPF) maps of the as-received fine grain and 'blocky alpha' large grain samples before hydrogen charging are given in Figure 1 In the fine grain material, most of the hydrides are found at grain boundaries. Macroscopically, the interconnected hydride stringers align perpendicular to ND, in agreement with the observations in the literature [22,29]. In the large grain sample, three types of hydrides are observed which can be described in terms of their different nucleation sites:…”

Section: General Hydride Distributionsupporting

confidence: 90%

“…It was reported that δ phase Zr hydrides tend to form preferentially at grain boundaries under slow cooling rates [17][18][19][20]. In Zircaloy-4, it has been found that the crystallographic orientation relationship (OR) between hexagonal close packed (HCP) α-Zr matrix and FCC δ-hydride is {0001} ||{111} ; < 112 ̅ 0 > || < 110 > [19,[21][22][23], and the habit planes of the macroscopic hydride packets are the {101 ̅ 7} planes, which are close to the basal plane (~14.7°), of the surrounding α-Zr matrix [24,25]. The precipitation of δ-hydride in α-Zr results in a dilatational volumetric strain of 17.2% locally [26], and this misfit is accommodated by dislocations observed within both the hydride and the matrix [27,28].…”

Section: Introductionmentioning

confidence: 99%

“…In textured Zircaloy it was observed that the hydride stringers align perpendicular to the sheet or tube normal direction (ND) [22,29]. In thin wall cladding tubes, the radial hydrides are extremely detrimental to the ductility of fuel claddings as compared to circumferential hydrides, the texture of the cladding materials is controlled through processing such that hydrides form circumferentially during operation [30,31].…”

Section: Introductionmentioning

confidence: 99%

“…However, the reason why hydrides orient along specific texture components of Zircaloy is still not well understood. Kumar et al [22] claimed that in textured Zircaloy-4 the intergranular hydrides form more easily in those grains with their basal planes oriented close to the grain boundaries, but no direct experimental evidence was provided. Theoretical calculations by Qin et al [32] found that both grain boundary structure and energy may influence the propensity for hydride nucleation, and intergranular hydrides tend to nucleate at high energy grain boundaries with one of the grains having its basal plane nearly parallel to the grain boundary.…”

Section: Introductionmentioning

confidence: 99%

“…Research efforts on hydride precipitation in Zr alloys so far are all carried out on as-received commercial Zircaloy cladding materials consist of relatively fine grains (around or less than 10 μm). Microstructural characterisation of δ phase hydrides in Zircaloy-4 using electron backscatter diffraction (EBSD) has significantly promoted the knowledge of the hydride distribution and hydride-matrix OR [21,22,27]. However, the focus of these works are mostly on the nature of the individual hydride packets instead of the interconnected hydride stringers which are of more significant industrial importance.…”

Section: Introductionmentioning

confidence: 99%

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Microstructure and Formation Mechanisms of δ-Hydrides in Variable Grain Size Zircaloy-4 Studied by Electron Backscatter Diffraction

Wang¹,

Giuliani²,

Britton³

2019

Microsc Microanal

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Microstructure and crystallography of δ phase hydrides in as-received fine grain and 'blocky alpha' large grain Zircaloy-4 (average grain size ~11 µm and >200 µm, respectively) were examined using electron backscatter diffraction. Results suggest that the matrix-hydride orientation relationship is {0001} ||{111} ; < 112 ̅ 0 > || < 110 > for all the cases studied. The habit plane of intragranular hydrides and some intergranular hydrides has been found to be {101 ̅ 7} of the surrounding matrix. The morphology of intergranular hydrides can vary depending upon the angle between the grain boundary and the hydride habit plane. The misfit strain between α-Zr and δ-hydride is accommodated by high density of dislocations and twin structures in the hydrides, and a mechanism of twin formation in the hydrides has been proposed. The growth of hydrides across grain boundaries is achieved through an autocatalytic manner similar to the growth pattern of intragranular hydrides. Easy collective shear along < 11 ̅ 00 > makes it possible for hydride nucleation at any grain boundaries, while the process seems to favour grain boundaries with low (<40°) and high (>80°) c-axis misorientation angles. Moreover, the angle between the grain boundary and the adjacent basal planes does not influence the propensity for hydride nucleation.

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Section: General Hydride Distributionsupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Microstructure and Formation Mechanisms of δ-Hydrides in Variable Grain Size Zircaloy-4 Studied by Electron Backscatter Diffraction

Wang¹,

Giuliani²,

Britton³

2019

Microsc Microanal

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Molecular Dynamics Study of Zirconium and Zirconium Hydride

Siripurapu¹,

Szpunar²,

Szpunar³

2013

Pricm

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Molecular dynamics (MD) simulations were used in order to investigate structure and mechanical properties of zirconium and zirconium hydride. Calculation of temperature dependent failure of zirconium, diffusion of hydrogen in zirconium, properties of interfaces in zirconium and zirconium hydride and effect of hydrogen on crack nucleation and propagation were in good agreement with available experimental data. These are the first computer simulations where large-scale atomic/molecular massively parallel simulator (LAMMPS) code was used with the Embedded Atom Method (EAM) and Modified Embedded Atom Method (MEAM) to study structure and mechanical properties of zirconium hydrogen system (Zr-H) and zirconium hydride (ZrH2).Verification of methods was done in order to establish the best potential for zirconium and zirconium hydride. EAM and MEAM potentials successfully predicted lattice parameters, mechanical properties and variation of lattice parameters with temperature for α-Zr. MEAM potential was used to predict correctly the face centered structure for ZrH2 and also its mechanical properties.Temperature dependent stress-strain curves were calculated in order to predict yielding point for α-Zr. Results indicate early yielding and failure with increase of temperature in zirconium on application of tensile and compressive strains. Anisotropic stress variation with temperature in α-Zr was calculated.Hydrogen ingress through diffusion of hydrogen in zirconium is a mechanism responsible for formation of hydrides. Temperature-dependent hydrogen diffusion and activation energy for diffusion was calculated and the agreement with experiments was satisfactory. Anisotropy of diffusion of hydrogen is observed for Zr crystal. Hydrogen diffusion was also modeled under tensile and compressive strain and a possible formation of hydrides in the direction perpendicular to applied strain was observed.The effect of strain on orientation of hydride was investigated. Hydride {111} oriented crystal Bonds surrounding atoms and stress concentration analysis were performed using OVITO and VMD software respectively. Weaker bonds and higher stress concentrations are observed in the presence of hydrogen in zirconium. The presented results clearly demonstrate that MD simulation can be used to predict structure and processes that are important for understanding failure in Zr based nuclear materials.iv PREFACE Sections of this thesis have been submitted as a multi-authored paper in refereed conference papers. The research, data analyses and manuscript preparation were carried out by me and the co-authors contributed in editing the manuscripts for submission to refereed conference papers.

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Imaging and hydrogen analysis by SIMS in zirconium alloy cladding: a dual ion beam approach

Mine

Portier

Martin

2014

Surface & Interface Analysis

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Zirconium-based alloys are used as fuel cladding material in nuclear power plants. During the reactor operation, the material is oxidized by the water (reactor coolant), and hydrogen gas is formed. The released hydrogen gas, which partly diffuses into the zirconium alloy, forms hydrides when the hydrogen solubility limit is exceeded. This may result in blistering and cracking of the claddinga phenomenon commonly known as hydrogen embrittlement. Both corrosion and H-uptake phenomena are limiting factors, which can reduce the time of life of cladding under irradiation in a power plant. This study concerns a preliminary investigation of hydrogen by SIMS in a hydrogenated but not-irradiated Zircaloy-4 sample in order to develop a better understanding of hydrogen ingression in high burn up irradiated cladding tubes. Although hydrogen can be easily detected using the SIMS technique, any contamination source of hydrogen must be well identified and minimized during the SIMS measurements. In this work, we have analyzed a hydrogenated (135 wppm in bulk) Zircaloy-4 cladding specimen. In the first step, the sample's surface has been presputtered with cesium ions. Thereafter, H À ions yield images have been acquired analyzing the sample with a gallium primary ion beam. Using this dual beam approach, the hydride precipitates present in the sample have been clearly identified and analyzed.

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Preferential precipitation of hydrides in textured zircaloy-4 sheets

Cited by 76 publications

References 28 publications

Microstructure and Formation Mechanisms of δ-Hydrides in Variable Grain Size Zircaloy-4 Studied by Electron Backscatter Diffraction

Microstructure and Formation Mechanisms of δ-Hydrides in Variable Grain Size Zircaloy-4 Studied by Electron Backscatter Diffraction

Molecular Dynamics Study of Zirconium and Zirconium Hydride

Imaging and hydrogen analysis by SIMS in zirconium alloy cladding: a dual ion beam approach

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