Zirconium Specimens Research Articles

The micromechanics of fracture of zirconium hydrides

Zirconium alloys are susceptible to hydrogen embrittlement and hydride precipitation. The precipitation of hydrides is accompanied by a transformation strain, but the contribution of this strain to the fracture of hydrides is not well-understood. In this study, deformation mechanisms and the micromechanics of fracture of hydrides are investigated by conducting in-situ and interrupted ex-situ tensile experiments on hydrided zirconium specimens. Electron backscatter diffraction (EBSD) is used to measure the macro-EBSD maps that contain the grains located in the gauge section of the specimens’ surfaces. Further, high spatial resolution EBSD is used to determine orientation variations induced by the precipitation of hydrides and by the external mechanical load. The measured grain orientations are mapped into a crystal plasticity finite element (CPFE) model to examine the performance of eight different crack initiation criteria. It is shown that a multiscale approach is essential for studying the fracture of hydrides as the details of hydride morphology, orientation, local grain neighborhood, and hydride-hydride interactions are important in such analysis. It is shown that neglecting the effects of hydride-induced transformation strain leads to inaccuracies in predicting both the location and direction of microcracks within hydrides. Among the examined methods, the combination of resolved shear stress and resolved shear strain on slip systems, i.e., the highest shear energy density, consistently predicts the correct locations of hydride microcracks as well as their propagation direction. Further, it is shown that the significant deformation that takes place within hydrides is the main driving force for the fracture of hydrides.

Feeder Pipe Oxidation in the Presence of Steam During a Nuclear Reactor Accident

A Canada Deuterium Uranium (CANDU) reactor has hundreds of carbon steel feeder pipes that are connected at one end to the fuel channels at the reactor face and are connected at the other end to the reactor inlet and outlet headers above the reactor. The production of hydrogen gas from metal–water interaction at high temperatures is a major concern during a severe accident in a nuclear reactor. It is generally accepted that the main source of hydrogen gas during a severe accident is the chemical interaction of Zircaloy fuel cladding and the water coolant. However, it has recently been suggested that the amount of hydrogen produced by the oxidation of carbon steel located outside of a CANDU core could exceed that produced by zirconium oxidation. In this work, the linear and parabolic oxidation rate constants of CANDU feeder carbon steel, in the temperature range of 600–1,100°C, were measured to be W/t = 1.806 × 103 exp (− 126,337/RT) and W2/t = 1.879 × 105 exp (− 135,835/RT), respectively. For parabolic steam oxidation beginning at roughly 90 minutes after reaching steady-state heating temperatures, the latter equation should be used. These rates are about a factor of 5–10 greater than oxidation rates measured in 304L stainless steel and in zirconium specimens, meaning that the carbon steel oxidation can be significant in an accident.

Impact of Carbon Ion Implantation on the Crystal Structure, Surface Morphology, Vickers Hardness and Electrochemical Corrosion of Zirconium

Specimens of polycrystalline zirconium were irradiated with 1 MeV singly charged carbon ions using Pelletron accelerator. The ion doses used were in the range 1013 ions/cm2-1015 ions/cm2. The pristine specimen had preferred orientation for (002) and (004) crystallographic planes, which remained unaffected on irradiation with carbon ions. The crystallite size and lattice strain initially increased on irradiation with carbon ion dose 1013 ions/cm2 and later on decreased monotonically with further increase in ion dose till 1015 ions/cm2. Lattice strain increased linearly with the crystallite size. FESEM micrographs showed that carbon ion irradiation on the smooth surface of pristine zirconium specimens produced surface defects in the form of pits, cavities, agglomers and protruded structures of height ≈ 26 µm, which modified the surface properties, such as surface roughness, surface hardness and corrosion resistance. The surface roughness increased substantially on irradiation with carbon ions till 1014 ions/cm2 and later on decreased a little bit from the peak value. The surface hardness followed the classical Hall–Petch relation. The corrosion resistance is significantly improved on irradiation with carbon ions; greater the ion dose better is the corrosion resistance.

Contact resistance prediction of zirconium joints welded by small scale resistance spot welding using ANN and RSM models

The total electrical resistance between electrodes is a major factor in small scale resistance spot welding process uncertainty. The initial resistance between electrodes is depending on the current profile, electrode force and dome radius of hemispherical electrodes. A comparison between the experimental results of the expected resistance between electrodes and the predicted values of using ANN and RSM methods is the main goal of this study. E110 zirconium alloy with a thickness of 0.25 + 0.25 mm and 440 MPa tensile strength is used. An increase in dome radius of hemispherical electrodes reduces mean resistance values for zirconium alloy. The rate of preheating current rise has no appreciable effect on stabilization of resistance between electrodes in all cases. Stepwise current rise significantly reduces dispersion of resistance values for zirconium alloy. However, their dispersion significantly decreases after preheating in comparison with initial values. The empirical model predicted by the response surface methodology (RSM) is compared with the backpropagation algorithm model of artificial neural networks (ANN). On zirconium specimens, the absolute maximum error in RSM technique was 9.92% while 4.43%in ANN. Furthermore, in most cases the absolute maximum error in ANN is lower than RSM.

Evolution of the Structural-Phase State of E110 Alloy Fuel Rod Claddings at High Temperatures and Stresses

The results of microstructural studies of the fragments of E110 alloy fuel rod cladding specimens based on sponge and electrolytic zirconium after the operation as a part of VVER-1000 fuel assemblies with the subsequent creep tests under axial loading are presented. It was shown that, during the creep tests, the studied specimens showed no changes in the chemical composition, average size, and bulk density of the second phases, including radiation-induced ones. It was found that, during the creep tests, dislocation loops were annealed, i.e., an increase occurred in their average size with a simultaneous decrease in bulk density. It was shown that the specimens of fuel rod claddings made of an alloy based on electrolytic zirconium demonstrated more significant creep resistance compared to the sponge-based zirconium alloy specimens, which is related to a higher density of globular β-Nb precipitates in the irradiated electrolytic zirconium specimens.

Evolution of the structural phase state of E110 fuel claddings under high temperatures and stress

The paper presents results of microstructural studies of E110 alloy specimens in fuel claddings based on sponge and electrolytic zirconium after operation in the fuel elements in VVER-1000. During the creep tests with axial loading no changes were observed in the studied specimens referring the chemical composition, average size and bulk density of the second phases, including radiation-induced ones. It was found that during creep tests, dislocation loops are annealed, i.e. an increase occurs in their average size with a simultaneous decrease in bulk density. It was shown that the specimens of fuel elements claddings from an alloy based on electrolytic zirconium demonstrate greater creep resistance compared with sponge based zirconium specimens, which is apparently linked with a higher density of globular β-Nb precipitates in the irradiated electrolytic zirconium specimens.

Dislocation structure in textured zirconium tensile-deformed along rolling and transverse directions determined by X-ray diffraction line profile analysis

Specimens of cold-rolled zirconium were tensile-deformed along the rolling (RD) and the transverse (TD) directions. The stress-strain curves revealed a strong texture dependence. High resolution X-ray line profile analysis was used to determine the prevailing active slip-systems in the specimens with different textures. The reflections in the X-ray diffraction patterns were separated into two groups. One group corresponds to the major and the other group to the random texture component, respectively. The dislocation densities, the subgrain size and the prevailing active slip-systems were evaluated by using the convolutional multiple whole profile (CMWP) procedure. These microstructure parameters were evaluated separately in the two groups of reflections corresponding to the two different texture components. Significant differences were found in both, the evolution of dislocation densities and the development of the fractions of <a> and <c+a> type slip systems in the RD and TD specimens during tensile deformation. The differences between the RD and TD stress-strain curves are discussed in terms of the differences of the microstructure evolution.

Quantitative and Qualitative Assessment of the Wear of Primary EnamelAgainst Three Types of Full Coronal Coverage

Aims: the objective of the study was to assess the wear of primary teeth against three types of crown coverage, both quantitavely and qualitatively. Methods: specimens of 30 extracted primary molars, were mounted against 10 specimens of zirconia crowns (group A), 10 specimens of preveneered stainless steel crowns (group B), and 10 extracted primary molars and 10 specimens of stainless steel crowns (group C) and were undergone in vitro wear testing using an abrasive machine. Measurement of the amount of weight loss was performed, in addition to a scanning electron microscopic examination of the worn enamel surfaces. Results: the greatest wear was recorded in zirconium specimens, and the lowest was in preveneered stainless steel crowns with a significant difference noted between the three groups (p<0.001).The micro-morphological wear characteristics revealed the most aggressive wear with complete loss of enamel structure in zirconium specimens. Conclusions: the zirconium crowns induced the most severe wear in primary molars, followed by stainless steel crowns, and the least wear was induced by preveneered stainless steel crowns.

A statistical analysis of the influence of microstructure and twin–twin junctions on twin nucleation and twin growth in Zr

The purpose of the present work is (1) to study the statistical relevance of twin–twin junctions and (2) to study statistically the influence of twin–twin junctions and microstructure on nucleation and growth of twins in h.c.p. materials. A new automated twin recognition technique has been developed and is used to extract statistics from EBSD scans of high purity clock-rolled zirconium specimens loaded along the through-thickness and one of the in-plane directions. The technique allows for recognition of tensile and compressive twin systems within each individual grain. The ten possible twin–twin junction types that may occur in Zr between first generation twins are introduced as well as their associated frequencies in cases of through-thickness and in-plane compression. The present study shows that twin–twin junctions between twins belonging to the most active twinning modes are statistically relevant. It is also shown that twin–twin junctions hinder twin growth. In agreement with previous studies, it is found that irrespective of the loading direction and twin mode, both grain size and crystallographic orientation largely influence the propensity of grains for twin activation. However, the study suggests large differences in nucleation and growth mechanisms for each twinning mode.

Investigation of anodic oxide coatings on zirconium after heat treatment

Abstract Herein, results of heat treatment of zirconium anodised under plasma electrolytic oxidation (PEO) conditions at 500–800 °C are presented. The obtained oxide films were investigated by means of SEM, XRD and Raman spectroscopy. The corrosion resistance of the zirconium specimens was evaluated in Ringer's solution. A bilayer oxide coatings generated in the course of PEO of zirconium were not observed after the heat treatment. The resulting oxide layers contained a new sublayer located at the metal/oxide interface is suggested to originate from the thermal oxidation of zirconium. The corrosion resistance of the anodised metal was improved after the heat treatment.

Analysis of the residual stress in zirconium subjected to surface severe plastic deformation

The residual stress of commercially pure zirconium specimens subjected to surface mechanical attrition treatment (SMAT) for different durations is measured with X-ray diffraction (XRD). XRD peak broadening analysis is conducted to obtain the distributions of the crystallite size, microstrain and dislocation density as functions of the depth from the processed surface. Finite element modeling is performed to reveal the characteristics of the residual stress distribution. Microstructure observation using optical and electron microscopy are also carried out in order to elucidate the residual stress development. The correlations between the microstructure features and the residual stress distribution in zirconium are examined. The results indicate that a more pronounced compressive residual stress field can be generated by the SMAT process compared to that obtained by conventional shot peening, and that the compressive residual stress distributions exhibit nonlinear variation with the distributions of the full width at the half maximum of the XRD profiles and the dislocation densities.

Influence of the structural state of zirconium on the sorption–desorption parameters of hydrogen

We study the interaction of hydrogen with zirconium in different structural states, i.e., from the nanocrystalline state to the coarse-crystalline state. The phase composition and structure of hydrides in hydrogenated zirconium specimens with different initial microstructures are determined. The kinetics of sorption of hydrogen by nanocrystalline zirconium at different temperatures and the desorption processes running in the course of continuous heating in vacuum are investigated. It is shown that the initial temperature of absorption, phase composition, and the amount of absorbed hydrogen strongly depend on the structural state of zirconium.

Breakup Time of Zirconium Shaped Charge Jet

AbstractThe Johnson‐Cook parameters for the zirconium material were determined based on the data obtained from the tensile testing of zirconium specimens at different strain‐rates and different temperatures. The velocity difference (VPL) between the particulated jet fragments was calculated for zirconium liners of different thicknesses using Johnson‐Cook constitutive equation. A breakup time formula for the zirconium shaped charge was proposed, which demonstrated better ductility performance than the copper shaped charge.

Influence of the preliminary radiation-oxidation treatment of zirconium on the radiation-heterogeneous processes in the Zr + H2O System

The oxidation processes are studied of untreated and radiation-oxidation preliminary treated (in an H2O2 solution at room temperature) zirconium specimens in contact with water by reflection-absorption infrared spectroscopy. A comparison is performed of their kinetic characteristics. Passivation of the metal surface is revealed as evidence of the surface oxide layer.

Indentation study of titanium, zirconium, and hafnium hydrides

AbstractMechanical properties of titanium, zirconium, and hafnium hydrides were evaluated by indentation tests in the present study. Single-phase bulk specimens of titanium, zirconium, and hafnium hydrides with a fluorite type structure were produced using a Sieverts' apparatus. The indentation hardness values of titanium and hafnium hydrides were lower than those of the pure metals and drastically decreased with increasing hydrogen content. The hardness of zirconium hydride was higher than that of pure zirconium and slightly depended on hydrogen content. The hardness of the hydrides decreased with increasing maximum indentation load, which has been referred to as indentation size effect. The dependences of hardness on the indentation depth for the hydrides were found to obey the Nix–Gao model. The indentation size effects for the hydrides were significantly smaller than those for the pure metals.

White Beam Microdiffraction Experiments for the Determination of the Local Plastic Behaviour of Polycrystals

The overall plastic behavior of polycrystalline materials strongly depends on the microstructure and on the local rheology of individual grains. The characterization of the strain and stress heterogeneities within the specimen, which result from the intergranular mechanical interactions, is of particular interest since they largely control the microstructure evolutions such as texture development, work-hardening, damage, recrystallization, etc. The influence of microstructure on the effective behavior can be addressed by physical-based predictive models (homogenization schemes) based either on full-field or on mean-field approaches. But these models require the knowledge of the grain behavior, which in turn must be determined on the real specimen under investigation. The microextensometry technique allows the determination of the surface total (i.e. plastic + elastic) strain field with a micrometric spatial resolution. On the other hand, the white beam X-ray microdiffraction technique developed recently at the Advanced Light Source enables the determination of the elastic strain with the same spatial resolution. For polycrystalline materials with grain size of about 10 micrometers, a complete intragranular mechanical characterization can thus be performed by coupling these two techniques. The very first results obtained on plastically deformed copper and zirconium specimens are presented.

Effect of copper ions implantation on corrosion behavior of zirconium in 1 M H 2SO 4

In order to study the effect of copper ion implantation on the aqueous corrosion behavior, specimens of zirconium were implanted with copper ions with fluences ranging from 1 × 10 16 to 1 × 10 17 ions/cm 2, using a metal vapor vacuum arc source (MEVVA) operated at an extraction voltage of 40 kV. The valence states and depth distributions of elements in the surface layer of the samples were analyzed by X-ray photoelectron spectroscopy (XPS) and auger electron spectroscopy (AES), respectively. Transmission electron microscopy (TEM) was used to examine the micro-structure of the copper-implanted samples. The potentiodynamic polarization technique was employed to evaluate the aqueous corrosion resistance of the implanted zirconium samples in a 1 M H 2SO 4 solution. It was found that a significant improvement was achieved in the aqueous corrosion resistance of zirconium implanted with copper ions. While the corrosion resistance of implanted samples declined with increasing the fluence. Finally, the mechanism of the corrosion behavior of copper-implanted zirconium was discussed.

Surface analysis and corrosion behavior of zirconium samples implanted with yttrium and lanthanum

Zirconium specimens were implanted with yttrium and lanthanum ions with a fluence ranging from 1×10 16 to 1×10 17 ions/cm 2 at approx. 130 °C, using a metal vapor vacuum arc source at an extraction voltage of 40 kV. The surfaces of the implanted samples were then analysed. The valence states of elements in implanted surface layer were analysed by X-ray photoelectron spectroscopy (XPS), which showed that yttrium existed in the form of Y 2O 3, and lanthanum existed in the form of La 2O 3. Depth distributions of elements in the implanted surface of samples were obtained by Auger electron spectroscopy (AES), which showed that the oxide film of zirconium substrate became thicker with increasing implantation fluence, the thicknesses of the oxide films reached the maximum approximately to the fluence of 1×10 17 ions/cm 2. Rutherford back-scattering indicates that a profile of La appears in Zr around the depth of 30 nm, which also indicates that a serious sputtering occurred during the (La+Y) 1×10 17 ions/cm 2 implantation. The potentiodynamic polarization technique was employed to evaluate the aqueous corrosion resistance of the implanted-zirconium samples in 0.6 M H 2SO 4. It was found that a significant improvement was achieved in the aqueous corrosion resistance of zirconium compared with that of as-received zirconium when the fluence is smaller than 5×10 16 (Y+La)/cm 2. The mechanism of the corrosion behavior of the implanted-zirconium samples was discussed.

Corrosion behavior in 1 N H 2SO 4 of zirconium ion implanted with nickel

In order to study the effect of nickel ion implantation on the aqueous corrosion behavior, specimens of zirconium were implanted by nickel ions with doses ranging from 1×10 16 to 5×10 17 ions/cm 2, using a MEVVA source at an extraction voltage of 40 kV. The valence states and depth distribution of elements in the surface layer of the samples were analyzed by X-ray photoelectron spectroscopy (XPS) and auger electron spectroscopy (AES), respectively. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to examine the micro-morphology and microstructure of the nickel-implanted samples. Potentiodynamic polarization measurements were employed to evaluate the aqueous corrosion resistance of the zirconium in a 1 N H 2SO 4 solution. In the first sweep polarization, the passive current densities at dose of 1×10 16 and 5×10 16 ions/cm 2 are lower than that of as received zirconium. While in the third sweep polarization, the passive current densities of all the implanted samples are higher than that of as received zirconium. Finally, the mechanism of the corrosion behavior of the nickel-implanted zirconium is discussed.

Deformation of zirconium irradiated by 4.4 MeV protons at 347 K

Proton irradiation tests have been performed on two cold-worked zirconium specimens using 4.4 MeV protons with controlled displacement damage rates between 1.4 and 6.9 × 10 −7 dpa s −1. The specimens had different Fe contents, nominally pure (NP): 64–70 ppm by weight, and ultra-high purity (UP): 3–5 ppm by weight. A stress of 50 MPa was applied during the tests, and the test temperature was 347 K.