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Hydrogen diffuses in zirconium alloys in response to gradients in hydrogen concentration, temperature, and stress. This essay discusses the results of several evaluations of the coefficient describing the effects of temperature gradients called the heat of transport. The values distinguish between when hydrogen is in solution, (25 ± 3) kJ/mol, and when stable hydrides are present, (116 ± 17) kJ/mol. [ABSTRACT FROM AUTHOR]

This study has established the radiation shielding efficacy of zircaloy-2 and zircaloy-4 over a wide spectrum of energy levels. Using the Monte Carlo method, the gamma and neutron transmission factors (TF and nTF) were calculated for various energy levels. Zircaloy-2 demonstrated the highest gamma-ray absorption capacity and the lowest neutron absorption capacity among the investigated alloys. The results indicate that zircaloy-2 and zircaloy-4 have nearly the same neutron transmission characteristics. Although many studies have examined the structure and physical characteristics of these materials, there has been a lack of Monte Carlo simulations to comprehensively investigate the correlation between gamma absorption, neutron absorption parameters, and mechanical qualities. This research aims to examine the ability of zirconium and its zircaloy-2 and zircaloy-4 alloys, which are critical materials used in the nuclear industry, to absorb gamma and neutron radiation over a broad spectrum of frequencies. According to the results, zircaloy-2 has the best ability to absorb secondary gamma rays and the highest level of resistance to them. Despite the minimal disparity in the nTF between the two alloys, simulation results have shown that zircaloy-2 has a higher level of neutron transmittance. These results have the potential to expedite the development of novel materials with enhanced attributes for various applications.

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Zirconium alloy with the composition of 90.1% Zr and alloying elements such as Mg, Al, and Si was investigated for its mechanical properties and corrosion resistance. The specimen was dissolved in a mixture of NaOH, Na2CO3, S, and SnO2 at 800°C for 10 min, followed by an HCl solution at room temperature for 100 cycles. The structural properties were characterized by X-ray diffraction and scanning electron microscopy, while the mechanical properties, such as tensile strength were investigated by a universal tensile machine. The microstructural observations indicated that the outside part of the crucible underwent pitting corrosion which resulted in corrosion in all directions inside that part of the crucible. The corrosion structure consisted of cracks that reached the base metal. The residual chemical from the fusion and dissolution process remained in the crack and formed NaCl, which accelerated the crack. The release rate of the zirconia oxide layer was calculated to be 8 μm per cycle. During the corrosion process at high temperatures, oxygen diffusion infiltrated the base metal and stretched the crystal lattice, causing strain hardening with the values of yield strength and ultimate tensile strength increased to 22.5% while the strain decreased by 50%. [ABSTRACT FROM AUTHOR]

Delayed hydride cracking (DHC) is a hydrogen embrittlement phenomenon that may potentially occur in Zircaloy-4 fuel claddings during dry storage conditions. An experimental procedure has been developed to measure the toughness of this material in the presence of DHC by allowing crack propagation through the thickness of a fuel cladding. Notched C-ring specimens, charged with 100 wppm of hydrogen, were used and pre-cracked by brittle fracture of a hydrided zone at the notch root at room temperature. The length of the pre-crack was measured on the fracture surface or cross-sections. Additionally, a finite element model was developed to determine the stress intensity factor as a function of the crack length for a given loading. Two types of tests were conducted independently to determine the fracture toughness with and without DHC, K I DHC and K I C , respectively: (i) constant load tests at 150 ∘ C, 200 ∘ C, and 250 ∘ C; (ii) monotonic tests at 25 ∘ C, 200 ∘ C, and 250 ∘ C. The results indicate the following: (1) there is no temperature influence on the DHC toughness of Zircaloy-4 between 150 and 250 ∘ C ( K I DHC ∈ 7.2 ; 9.2 MPa m ), (2) within this temperature range, the fracture toughness of Zircaloy-4 is halved by DHC ( K I C ∈ 16.9 ; 19.7 MPa m ), (3) the crack propagation rate decreases with decreasing temperature and (4) the time before crack propagation increases as the temperature and loading decrease. [ABSTRACT FROM AUTHOR]

The ability to economically offer distinct properties within a single component has gathered significant attention for bimetallic or cladded tubular components across various industries. A novel friction stir-based cladding method and its in-depth analyses to achieve internal cladding of Al inside the stainless steel (SS) tubes are presented. The process outcome with the variation in process parameters and its impact on heat generation and intermetallic compounds (IMCs) formation was analyzed. In this process, the joining between the base substrate and the cladded material is due to the heat generation that leads to interdiffusion and ultimately promotes the formation of IMCs. The mechanism of IMCs formation, its growth phenomenon, and its impact on joining efficacy were investigated. The cladded Al exhibited an approximately twofold increase in grain size compared to the base Al alloy, as revealed through electron back-scattered diffraction (EBSD) analysis. The coarser grains help to restrict the propagation of fracture during the flattening test. The cladded tube exhibits no sign of delamination after compression, which paves the way for the industrial adoption of the process. [Display omitted] • Friction stir backward extrusion based bimetallic tubular component fabrication. • Analysis of heat generation and its impact on the formation of IMCs. • Confirmation of Al-rich IMCs at the interface and its effects on bonding. • Uniform IMC layer thickness (3-4 µm) results in optimum bond strength at interface. • A twofold increase in the grain size of Al, resulting in resistance to delamination. [ABSTRACT FROM AUTHOR]

LZ91 Mg-Li alloy plates with three types of initial texture were rolled by 70% reduction at both room temperature and 200 °C to explore the rolling texture formation of α-Mg phase. The results showed that the rolling texture is largely affected by the initial texture. All the samples exhibited two main texture components as RD-split double peaks texture and TD-split double peaks texture after large strain rolling. The intensity of the two texture components was strongly influenced by the initial orientation and rolling temperature. Extension twinning altered the large-split non-basal orientation to a near basal one at low rolling strain. The basal orientation induced by twinning is unstable, which finally transmitted to the RD-split texture. The strong TD-split texture formed due to slip-induced orientation transition from its initial orientation. The competition between prismatic 〈 a 〉 and basal slip determined the intensity and tilt angle of the TD-split texture. By increasing the rolling temperature, the TD-split texture component was enhanced in all three samples. Limitation of extension twinning behavior and the promotion of prismatic slip at elevated temperature are the main reasons for the difference in hot and cold rolling texture. [ABSTRACT FROM AUTHOR]

In pressurized water reactors, LiOH may be concentrated in some areas, leading to the accelerated corrosion of fuel claddings. Injecting boric acid into primary coolants can mitigate the accelerated corrosion effect of LiOH on Zircaloys, but the effects of boron content on the corrosion behavior of the Zr-Sn-Nb alloy are still unknown. This work focused on the corrosion and hydrogen absorption behavior at 360 °C/18.6 MPa in 100 mg/kg LiOH solutions with 0 mg/kg, 50 mg/kg, and 200 mg/kg boron contents for up to 510 days, aiming to study the effect of boron content on corrosion resistance in LiOH solutions. Corrosion kinetics, microstructures of oxide films, hydrogen absorption concentrations and hydride morphology were obtained after the test. The results show that injecting boron in LiOH solutions can significantly reduce the corrosion weight gain, hydrogen concentration, and hydrogen length of Zr-Sn-Nb alloys, that is, improving corrosion resistance effectively. During the oxidation of the Zr-Sn-Nb alloy, B3+ and Li+ incorporate in oxide films. The incorporation of Li+ may lead to the generation of oxygen vacancies, which can carry oxygen from the solutions to O/M interface, accelerating corrosion. The incorporation of B3+ in oxide films will slow down the oxidation of Zr-Sn-Nb alloys by reducing the oxygen vacancies caused by Li+ aggregation. [ABSTRACT FROM AUTHOR]

The present study demonstrates the development of novel Ti-xZr (x = 5, 10, 15 and 20 wt.%) via vacuum sealing-assisted sintering technique. The microstructure, phase composition, physical, mechanical, tribological properties, and electrochemical corrosion behavior were investigated for biomedical applications. The phase composition and microstructure show the presence of α phases in as-prepared alloys. The alloys exhibit elevated hardness levels (477.59 ± 30.22 HV to 539.05 ± 27.09 HV), surpassing commercially pure titanium (cpTi, 200.26 HV) and Ti-6Al-4V (340.51 HV). Tribological studies of Ti-15Zr displays superior antifriction and antiwear properties, with a friction coefficient of 0.22 and a wear rate of 1.23 × 10–7 mm3 per mm of sliding distance. All alloys exhibit commendable corrosion resistance in simulated body fluid, with the Ti-20Zr alloy displaying a minimum corrosion rate of 1.29 µm/year. In conclusion, the synthesized alloys demonstrate the substantial potential for biomedical applications, particularly in orthopedic and dental implants, due to enhanced mechanical characteristics, wear resistance, and corrosion resistance. [ABSTRACT FROM AUTHOR]

Surface modification techniques play an important role in adjusting the physicochemical properties of titanium and its alloys. To reduce the penetration of alloying element ions into the body, various types of oxide coatings are used to protect it from the corrosive environment. Another important issue related to the surface layer requirement is ensuring an appropriate set of mechanical properties. Accordingly, in this study, the mechanical and electrochemical properties of the silicon dioxide layers formed by the deposition of nano physical vapor deposition on the surface of titanium and titanium 13‐niobium 13‐zirconium alloy samples were investigated. To evaluate the mechanical properties of the layers produced by this method, hardness tests were carried out, as well as tests on the adhesion of these layers to the metal substrate. On the other hand, electrochemical properties were studied using potentiodynamic measurements to assess the resistance to pitting corrosion, followed by impedance measurements to interpret the processes and phenomena occurring at the silicon dioxide layer/electrolyte interface. The data obtained showed different mechanical and electrochemical properties of the silicon dioxide layers generated with varying process parameters. [ABSTRACT FROM AUTHOR]

Operated under extreme conditions, corrosion occurs between zirconium alloy cladding tubes and the coolant in the primary loop of pressurized water reactors (PWRs), contributing to a reduction in the effective metallic material thickness. Therefore, understanding the corrosion behavior of zirconium alloy is vital to both raising the burnup of PWR and the improvement of safety properties of these reactors. During the past decades, extensive investigation was conducted with various conditions, such as changing corrosion temperatures and alloying elements, but contradiction persists and universal conclusion remain elusive. In the present work, a variety of research results that focused on corrosion kinetics, microstructural evolution, and the influence of alloying elements were integrated and summarized, so that a valuable reference can be provided to further research. [ABSTRACT FROM AUTHOR]

In this work, fuzzy model was developed that predicts response parameters and surface properties of an electrical discharge machined Zircaloy-2. Taguchi L18 mixed design was used to perform the experiments using different process parameters (polarity, pulse-on-time, pulse-off-time, tool electrode material, and peak current). Material removal rate (MRR) and tool wear rate (TWR) were chosen as machining response parameters, whereas number of particles (NoP) and the percentage particle area (PPA) for surface properties of EDMed surface. Digital image processing tool was used to evaluate the surface properties. Fuzzy-Sugeno (FS)-model was developed to predict MRR, TWR, NoP, and PPA. Model accuracy was found to be 94% for MRR and TWR, and 92% for NoP and PPA. Maximum MRR 1.53 × 10−3 mm3/min found when machining was performed using graphite tool with negative polarity. Fuzzy Sugeno-GRA method was successfully implemented to predict optimal response corresponding to high value of GRG. [ABSTRACT FROM AUTHOR]

The microstructure evolution associated with the cold forming sequence of an Fe-14Cr-1W-0.3Ti-0.3Y2O3 grade ferritic stainless steel strengthened by dispersion of nano oxides (ODS) was investigated. The material, initially hot extruded at 1100 °C and then shaped into cladding tube geometry via HPTR cold pilgering, shows a high microstructure stability that affects stress release heat treatment efficiency. Each step of the process was analyzed to better understand the microstructure stability of the material. Despite high levels of stored energy, heat treatments, up to 1350 °C, do not allow for recrystallization of the material. The Vickers hardness shows significant variations along the manufacturing steps. Thanks to a combination of EBSD and X-ray diffraction measurements, this study gives a new insight into the contribution of statistically stored dislocation (SSD) recovery on the hardness evolution during an ODS steel cold forming sequence. SSD density, close to 4.1015 m−2 after cold rolling, drops by only an order of magnitude during heat treatment, while geometrically necessary dislocation (GND) density, close to 1.1015 m−2, remains stable. Hardness decrease during heat treatments appears to be controlled only by the evolution of SSD. [ABSTRACT FROM AUTHOR]

A dense and continuous Cr coating with a thickness of approximately 140 μm was successfully deposited on the surface of a thin-walled Zr alloy cladding tube using high-speed laser cladding technology in this study. The microstructure, phase composition, microhardness, and resistance to high-temperature oxidation of the coating were investigated. The experimental results showed that the Cr coating exhibited high-strength metallurgical bond with the Zr alloy substrate, forming a narrow heat-affected zone with a thickness of 25 μm, and the coating consists of ZrCr2 and α-Zr phase. The average microhardness of the coating was 589 HV0.05, about 2.3 times that of the substrate. After oxidation at 1200 °C for 1200 s in air, with the formation of complete and dense protective Cr2O3 scale, the Cr-coated Zr alloy cladding tube showed better high-temperature oxidation resistance than uncoated tube. [ABSTRACT FROM AUTHOR]

Jetting in cylindrical cumulation is an elusive process. This paper investigates cumulative jetting during the compression of cylindrical shells by means of a hydrodynamic model and numerical simulation. A method for improving jetting in cylindrical cumulation that increases the radial velocity of shell convergence has been proposed and substantiated. The critical factor in the jet-formation zone—high temperature—is outlined. A method of normalizing the temperature in the jet-formation zone using a small diameter tube inside the main cladding made of refractory niobium has been proposed. Thus, suggestions were made to improve cumulative jetting in cylindrical cumulation. [ABSTRACT FROM AUTHOR]

• < a > loops nucleate below 0.05 dpa and the density reached saturation at 0.1 dpa in Zircaloy-2 under low-dose Ni3+ ion irradiation at 573 K. • Radiation-induced hardening occurs below 0.05 dpa due to the nucleation and growth of < a > loops. • The Orowan equation was used to calculate the contribution of < a > loops to the hardening effect, with an obstacle strength factor of 0.25. • The effect of applied stress on radiation-induced hardness was discussed. The microstructural evolution and hardening of Zircaloy-2 under low-dose irradiation (<1.0 dpa) with 3.2 MeV Ni3+ ions under applied stress at 573 K were investigated using transmission electron microscopy (TEM) examination and nano-indentation measurements in this study. The irradiation doses ranged from 0.05 to 1 dpa. The formation of < a > loops was observed at doses below 0.05 dpa, and the density was found to be saturated at about 0.1 dpa. The < a > loops then grew and intersected with adjacent loops to become entangled at doses above 0.4 dpa. Radiation-induced hardening was confirmed in Zircaloy-2 at the early stage of irradiation below 0.1 dpa, and the hardening effect was attributed to the nucleation and growth of < a > loops. The Orowan equation was used to estimate the contribution of dislocation loops to the hardening, and the estimated values were in good agreement with the experimental results, with the obstacle strength factor of < a > loops as 0.25. Furthermore, the effect of applied stress of 1 dpa irradiated tensile samples on radiation-induced hardening was also discussed. This study provides dislocation loop formation and hardening behavior of Zircaloy-2 under low-dose irradiation at 573 K with stress conditions. [ABSTRACT FROM AUTHOR]

In the present study, the dense Cr and Cr0.92Si0.08 coatings have been deposited on Zircaloy-4 substrates by the magnetron sputtering technique. The high-temperature oxidation resistance of coatings is evaluated in 1200 °C steam for 1–4 h. The Cr0.92Si0.08 coating shows better oxidation resistance than the Cr coating. The in-situ formed Zr2Si diffusion barrier inhibits the mutual diffusion of Cr and Zr. And the formation of a Cr2O3/SiO2 double-layer scale effectively improves the oxidation resistance of a single Cr2O3 layer. The formation of the in-situ diffusion barrier, Cr2O3/SiO2 scales and oxidation protection mechanisms of the Cr0.92Si0.08 coating have been discussed in detail. [ABSTRACT FROM AUTHOR]

Zirconium alloys are critical material components of systems subjected to harsh environments such as high temperatures, irradiation, and corrosion. When exposed to water in high temperature environments, these alloys can thermo-mechanically degrade by forming hydrides that have a crystalline structure that is different from that of zirconium. Cracks can nucleate near these hydrides; hence, these hydrides are a direct link to fracture failure and overall large inelastic strain deformation modes. To fundamentally understand and predict these microstructural failure modes, we interrogated a finite-element database that was deterministically tailored and generated for large strain-dislocation-density crystalline plasticity and fracture modes. A database of 210 simulations was created to randomly sample from a group of microstructural fingerprints that encompass hydride volume fraction, hydride orientation, grain orientation, hydride length, and hydride spacing for a hydride that is physically representative of an aggregate of a hydride population. Machine learning approaches were then used to understand, identify, and characterize the dominant microstructural mechanisms and characteristics. We first used fat-tailed Cauchy distributions to determine the extreme events. A multilayer perceptron was used to learn the mechanistic characteristics of the material response to predefined strain levels and accurately determine the critical fracture stress response and the accumulated shear slips in critical regions. The predictions indicate that hydride volume fraction, a population-level parameter, had a significant effect on localized parameters, such as fracture stress distribution regions, and on the accumulated immobile dislocation densities both within the face centered cubic hydrides and the hexagonal cubic packed h.c.p. matrix. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The current research focuses on laser melting and successive analysis of laboratory-scale uranium dioxide nuclear fuel samples in direct contact with Zircaloy-4 cladding. The goal was to characterize the melted and refrozen interfaces, in particular, observing local changes of the melting point and interdiffusion of fuel and cladding materials under inert gas (Ar), in the presence of hydrogen (Ar + 6% H2) or in air. Results obtained by laser heating UO2 pellets clad in a Zircaloy ring were interpreted in light of reference tests performed on pellets in which UO2 and zirconium were blended in a series of given compositions. The sample composition was analyzed by scanning electron microscopy to verify the occurrence of diffusion and segregation phenomena during the laser-heating cycles. Laser-melting experiments were performed on pellets of uranium dioxide clad in Zircaloy-4 rings to simulate the configuration of a light water reactor fuel rod. Under inert gas, the material interdiffusion resulted in consistent melting point depression (of up to 200 K below the melting point of pure UO2) at the interface between the fuel and the cladding. Experiments carried out in the presence of H2 displayed a more limited effect on the melting temperature, but they resulted in a remarkable embrittlement of the whole structure, with large fragmentation of the Zircaloy cladding. This was probably due to the formation of brittle and highly volatile Zr hydrides. The observed melting point decrease was even more pronounced (up to over 400 K) under air in uranium-rich samples, due to the change in the stoichiometry of UO2 in UO2+x. [ABSTRACT FROM AUTHOR]

A new cladding process is proposed and implemented on a bimetallic tube of copper and aluminum. Obtaining a good mechanical bond between the tube’s layers using simple setup components with low required process force and without using heating are the most distinguishing feature of this study. The objective of this paper is to study the effect of using three different spherical tipped punch diameters (21 mm, 21.6 mm, and 22 mm) on the cladding process. A spherical punch with a slightly enlarged spherical tip was pressed into the clad tube. To study the dynamical analysis of the developed process, an FE model was developed using ANSYS workbench®. The bonding of an AL6082T6 Aluminum tube (as the clad tube) to a pure copper tube (as the base tube) was studied. FE analysis results showed that increasing ball tipped punch diameter leads to an increase in the required process force, the deformation magnitude, the equivalent plastic strain, the maximum principal stress, and the maximum principal elastic strain values. The required process force was measured experimentally and by FE simulation for the three different ball tipped punch diameters. The average values of the FE process forces were found to be 21 KN, 39 KN and 48 KN respectively for the mentioned diameters, while experimentally the average forces values were found to be 13.3 KN, 33 KN and 39 KN for the mentioned diameters, respectively. A 10 KN force was required to dismantle the bimetallic tube layers using shear punch test. [ABSTRACT FROM AUTHOR]

• The mechanisms and influencing factors for the initiation of hot cracks (solidification crack, liquation crack, and ductility-dip crack) as well as cold cracks in the cladding layer of nickel-based high-temperature alloys formed by laser-based directed energy deposition are reviewed and discussed. • The propagation mechanisms of cracks after initiation during the forming process are reviewed and analyzed from the point of view of oxygen-induced crack propagation and the interactions between defects. • The main methods for inhibiting crack initiation and propagation are summarized. • Suggestions for future research are given on the mechanisms, influencing factors, and inhibition methods of crack initiation and propagation. Laser-based directed energy deposition (L-DED) has a broad application prospect in the preparation of complex structural parts, the repair of critical parts, and other aspects of Ni-based high-temperature alloys. However, the rapid solidification rate of the melt pool during the L-DED forming process, as well as the forming process characteristic of track-by-track overlapping of the cladding tracks and layer-by-layer stacking of the cladding layers, make it easy for defects, such as cracks, to appear in the multi-layer cladding layer of Ni-based alloys. Crack initiation brings hidden danger to the multi-layer cladding layer in subsequent service, and the propagation of the crack after initiation determines the final mechanical properties of the cladding layer. This paper reviews and discusses the initiation mechanisms of hot and cold cracks during the L-DED forming process, reviews and analyzes the propagation mechanisms after crack initiation in combination with the process characteristic of L-DED, and summarizes the influencing factors of crack initiation and propagation. Based on this, the main methods to inhibit crack initiation and propagation are further reviewed. The work in this paper aims to provide reference and guidance for realizing effective inhibition of crack initiation and propagation during L-DED forming of Ni-based high-temperature alloys. [ABSTRACT FROM AUTHOR]

This work evaluates the stress relaxation behavior of textured Zircaloy-4 cladding to understand how mechanical anisotropy influences pellet-cladding interactions. Uniaxial and biaxial stress relaxation tests are performed using full-tube axial tension and internal pressurization, respectively, aiming to achieve 0.25 %, 1 %, and 2 % equivalent strains in the cladding samples at a temperature of 300 °C. Internal pressure relaxation test results display enhanced stress relaxation compared to axial testing results, particularly for samples loaded beyond yield. Results of electron backscatter diffraction indicate increased deformation microstructure during loading and increased strain homogenization and recovery during relaxation for samples loaded via internal pressurization. Analysis indicates that the increased production and activity of basal 〈 a 〉 dislocations play a significant role in the enhanced relaxation measured in samples subjected to internal pressurization. [ABSTRACT FROM AUTHOR]

[Display omitted] • The structural evolution of the oxide layer on Zr-4 fuel cladding is characterized. • The high-temperature and high-pressure environment induces the transition in ZrO 2. • Prolonged oxidation leads to the formation of cracks in the oxide layer. • The nucleation, growth and agglomeration behaviors of Fe 3 O 4 and NiFe 2 O 4 are revealed. The essential safeguard provided by cladding tube in pressurized water reactor for nuclear fuel assembly leads to an investigation into the fouling behavior of Zircaloy-4 fuel cladding. This was carried out through a combination of experiments and simulations, employing a purpose-designed autoclave to simulate the flow fouling deposition under high-temperature high-pressure condition. The microstructures of the fouled samples were characterized, and the water chemistry of the corroded solution was analyzed. Furthermore, molecular dynamics simulations offered valuable insights into the binding mechanism, capturing the deposition behavior on the oxide surface and the agglomeration of molecules from a nanoscale perspective. [ABSTRACT FROM AUTHOR]

A comprehensive study of ZrCr 2 Laves phases is important for both fundamental research and technological applications. The ZrCr 2 compound is a typical precipitate observed in Zr-based alloys including the newly developed Cr-coated Zr cladding known as Accident Tolerant Fuel cladding. The brittle behavior of the Laves phases and the low melting point at the interface zone between the precipitates and the Zr matrix are considered as governing the thermomechanical behaviors of these newly developed nuclear fuel claddings for normal operating conditions but more dramatically in case of Loss Of Coolant Accident (LOCA) conditions. The aim of the present study is to investigate the various ZrCr 2 Laves polymorphs and their thermodynamic features particularly where conflicts exist in the literature. Based on diffraction experiments of annealed samples, it has been established that the transformation from the C14 high-temperature form to the C15 low-temperature form is of displacive nature without the C36 polymorph forming as an intermediate phase. The stable and metastable domains of C14 and C15 and their thermodynamic properties have been determined. The specific heat of both C14 and C15 types was measured over a wide range of temperatures from 2 to 1063 K by coupling relaxation calorimetry and DSC. The experimental data were fitted using a modified Einstein model. The room temperature entropies of the C14 and C15 phases were evaluated. The enthalpy of formation was measured for the first time using drop solution calorimetry in liquid Al at 1173 K in a Tian–Calvet calorimeter. The experimental value is in good agreement with Density Functional Theory (DFT) calculations. Finally, all these new results are discussed regarding the abundant literature on the ZrCr 2 Laves phases. • The stability of the ZrCr 2 Laves phase polymorphs is studied using various experimental techniques and DFT calculations. • The study does not confirm that the C36 polymorph is a stable intermediate phase in the system. • The thermodynamic properties of C14 and C15 polymorphs are measured using complementary calorimetric techniques. • The enthalpies of formation calculated by DFT agree well with the measured values. [ABSTRACT FROM AUTHOR]

• The thermal–mechanical coupled constitutive models and stress update algorithm of U-50Zr are proposed to carry out the multi-physics coupled modeling. • The thermomechanical coupled performance of 3 × 3 HCF rods are analyzed under both long-time irradiation and accident conditions. • The mechanical self-supporting effect between adjacent HCF rods is investigated to evaluate the stress and plastic deformation of zircaloy claddings. • The porosity effects of HCF rods induced by fission products are studied based on the thermal–mechanical responses under different burnups. Helical cruciform fuel (HCF) has strong potential for power uprate in nuclear reactors, due to enhanced turbulent mixing and heat transfer capacity. Accounting for the self-supporting effect between adjacent HCF rods, the thermal–mechanical coupled responses are unclear especially under high burnup condition. In this work, the thermomechanical coupled constitutive model and stress update algorithm of U-50Zr are proposed, and the multi-physics coupled simulations on 3 × 3 U-50Zr HCF rods are carried out under normal, RIA and LOCA conditions. Results show that the maximum temperature is less than 620 K and no sensitive to burnups and porosity. The low temperature indicates large thermal safety margins in case of accidents happening. As the burnup reaches to 6.43 % FIMA, the peak stress would increase to 262 MPa at the blade cladding region. Generally, the long cycle lifetime and robust fuel performance make U-50Zr HCF a good candidate for application under extreme scenarios. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effect of Fe addition and ion irradiation on hardening behavior in Zr alloys is experimentally investigated. • The formation of dislocation loops and amorphization of precipitation particles are facilitated through ion irradiation. • The quantitative contribution of underlying hardening mechanisms in irradiated Zr alloys is theoretically analyzed. • Theoretical results match well with different sets of unirradiated and ion-irradiated experimental data. Exploring the effect of Fe addition and ion irradiation on surface hardness in Zr alloys not only elucidates the strengthening mechanisms of individual alloying elements but also facilitates the assessment of mechanical properties under varying damage levels. In this work, the microstructural variations and surface hardness of Zr and Zr-Fe alloys were examined through Ne+ and Au3+ irradiation experiments. Electron backscatter diffraction (EBSD) characterization suggested the potential of Fe addition in Zr-Fe alloys for grain refinement. Transmission Electron Microscopy (TEM) observations indicated the formation of dislocation loops in irradiated materials, accompanied by a transformation of Zr 3 Fe particles from a crystalline to an amorphous state. Furthermore, nano-indentation tests were employed to measure the depth-dependent hardness, revealing an augmentation in hardness with increasing Fe content and highlighting noticeable irradiation hardening in Zr alloys. A mechanical model was then developed to theoretically investigate the contribution of diverse hardening mechanisms in ion-irradiated Zr alloys, particularly addressing the impact of non-uniformly distributed defects. Theoretical analysis denoted that the irradiation-induced defects hardening at varying depths follows distinct laws, whereas the precipitation hardening in Zr-Fe alloys was attributed to high-density strengthening particles induced by Fe addition. Moreover, it was determined that the surface hardness is governed by geometrically necessary dislocations (GNDs) and irradiation-induced defects at shallow depths, whereas precipitates and statistically stored dislocations (SSDs) dominate at relatively larger depths. [ABSTRACT FROM AUTHOR]

The slip strength of individual slip systems at different strain rates will control the mechanical response and strongly influence the anisotropy of plastic deformation. In this work, the slip activity and strain rate sensitivity of the basal, prismatic, and pyramidal slip systems are explored by testing at variable strain rates (from 10−4 s−1 to 125 s−1) using single crystal micropillar compression tests. These systematic experiments enable the direct fitting of the strain rate sensitivities of the different slips using a simple analytical model and this model reveals that deformation in polycrystals will be accommodated using different slip systems depending on the strain rate of deformation in addition to the stress state (i.e. Schmid's law). It was found that the engineering yield stress increases with strain rate, and this varied by slip systems. Activation of the prismatic slip system results in a high density of parallel, clearly discrete slip planes, while the activation of the pyramidal slip leads to the plastic collapse of the pillar, leading to a 'mushroom' morphology of the deformed pillar. This characterization and model provide insight that helps inform metal forming and understanding of the mechanical performance of these engineering alloys in the extremes of service conditions. [Display omitted] [ABSTRACT FROM AUTHOR]

• Cr-Nb coating prepared on Zr alloys. • Nb coating can restrain the inward diffusion of cr. • Complete miscibility between Nb and Zr lead to the fast consumption of the Nb coating. • Early-stage microstructure evolution of the sample was analyzed. Although the Cr-coated Zr alloys are considered as the most promising accident tolerant fuel cladding materials in recent years, the Cr-Zr interdiffusion problem is a major obstacle for the widely used of the Cr coating. In this study, Cr-Nb coated Zr alloy samples were prepared by magnetron sputtering. The Nb layer was designed as a barrier layer to retard the Cr-Zr interdiffusion. By using a fast-in and fast-out equipment, short time annealing was conducted in argon environment to study the coating evolution in high temperature environment. Results show that the Nb coating can retard the inward diffusion of Cr because of the low diffusion coefficient of Cr in the Nb layer. However, the complete miscibility between Nb and Zr lead to the fast consumption of the Nb coating. After 10 min annealing at 1200 °C, the 2.5 μm Nb coating disappeared, and a Cr-Zr-Nb mixed phase formed between the residual Cr coating and Zr substrate. The early-stage microstructure evolution of the sample was analyzed, and the barrier effect of the Nb coating was summarized. [ABSTRACT FROM AUTHOR]

• Flawless chromium based coatings improve zirconium alloy corrosion behaviour in lithium containing environment. • Optimised manufacturing process of thin coatings is the most critical part in ensuring the positive effect on corrosion rate of the substrate material. • Electrochemical Impedance Spectroscopy is a viable method for in-situ corrosion monitoring of accident tolerant fuel cladding materials in lithium containing environment. • Electrochemical Impedance Spectroscopy can be used for detection of local damage in thin layer based ATFs. Recent research indicates that one of the leading candidates for Accident Tolerant Fuels (ATF) are chromium-based coatings deposited on the commercially used zirconium alloys. The chromium-based coatings seem to improve the corrosion kinetics of underlying zirconium in both primary water and steam, where zirconium fails to meet the safety requirements. It is well known that the corrosion kinetics of zirconium can be negatively influenced by high concentrations of lithium ions. To evaluate the effect of chromium-based coatings on corrosion behavior of zirconium alloys in water containing elevated concentrations of lithium, Cr and CrN/Cr multilayer coated Zr1Nb alloy was tested in high temperature water containing 70 ppm Li+. Using Electrochemical Impedance Spectroscopy (EIS), Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray Spectroscopy (EDX), we have found that the chromium coating could have a positive effect on the underlying material as it behaves as a good diffusion barrier for oxygen and Li+ions. On the other hand, CrN/Cr coating, due to not sufficient structural integrity of the multilayer, showed non-protective behavior to the Zr1Nb alloy. Our results suggest that certain chromium coatings can significantly enhance corrosion resistance in lithium containing water environments. [ABSTRACT FROM AUTHOR]

Chromium (Cr) has been recognized as a promising diffusion barrier candidate to mitigate the Fuel Cladding Chemical Interaction (FCCI) failure in metallic fuels for sodium-cooled fast reactor. This paper, for the first time, conducted an in-depth post-irradiation examination of the microstructure and composition evolution, and micromechanics of the Cr diffusion barrier in U-10Zr fuel/HT9 cladding irradiated in the Advanced Test Reactor (ATR) to 8.7% burnup at an averaged Peak Inner Cladding Temperature of 540–550 °C. Transmission Electron Microscope (TEM) characterization confirmed the preferential intergranular diffusion of Zr and U in the Cr diffusion barrier, suggesting that grain boundaries served as fast path for the diffusion of Zr and U into the Cr diffusion barrier. The interaction zone is dominated by nano crystalline α- ZrCr 2 Laves phase. Despite the interaction, there is no microcracks being observed in the preserved Cr diffusion barrier and HT9 cladding, serving as a good barrier to mitigate FCCI under the studied in-reactor irradiation conditions. High density cavities in uniform distribution are observed inside Cr grains, nano particles contains Cr, Mn, and O are confirmed by Electron Energy Loss Spectroscopy (EELS) analysis. However, it is unclear whether the cavities will become an issue to the barrier integrity at higher burnup. In-situ Scanning Electron Microscopy (SEM) micro-tensile testing uncovered mechanical softening in the HT9 cladding nearing the Cr diffusion barrier, possibly due to the coarsening of lath structure and carbides precipitates. [ABSTRACT FROM AUTHOR]

It is significantly important to improve the corrosion resistance of Zr-Sn-Nb alloys in dissolved oxygen (DO) high temperature water by compositional modification. Here, the effect of Cu addition on the corrosion behaviors of Zr-0.5Sn-0.2Nb-0.4Fe-0.2Cr alloy was studied by using an autoclave circulating water loop at 360 °C/20 MPa up to 250 days. The oxide microstructures were characterized by a combination of SEM, TEM, STEM-EELS and PED. The results showed that compared with 0Cu alloy and 0.07Cu alloy, 0.13Cu alloy shows better corrosion resistance and its final weight gain after 250 days exposure is even lower than that of commercial Zr-4 alloy. The oxides for 0.07Cu and 0.13Cu alloys show more ordered crystals, thinner oxide and less lateral cracks, and the columnar grains show a stronger {10–3} texture, compared to Cu-free counterpart. The t-Zr 2 Cu SPPs have oxidized in the oxygen-rich layer below the O/M interface. The Cu ions tend to diffuse towards the grain boundary of dense columnar grains and maybe strengthen the grain boundaries, avoiding the defect generation under intrinsic stress in the oxide. [ABSTRACT FROM AUTHOR]

The hydrogen terminal solubilities for dissolution (TSSD) and precipitation (TSSP) in non-irradiated sponge-based E110opt alloy and electrolytic zirconium E635 alloy are presented. TSS measurements for these alloys were made for the first time. Samples were examined using the methods of differential scanning calorimetry (DSC) and hot vacuum extraction spectrometry. Terminal solid solubilities (TSSD and TSSP) in E110opt and E635 alloys are shown to be coincident with each other within the experimental uncertainty interval. This means that there is no distinguishable difference between TSS in sponge-based and electrolytic zirconium alloys. Resulting TSSD values for E110opt and E635 alloys were compared with those for zirconium alloys Zircaloy-2, Zircaloy-4, Zr-1%Nb, M5, Zirlo and shown to be identical within the errors. Approximation dependencies of TSSD and TSSP solvi in E110opt and E635 alloys were derived. These dependencies will be used in nuclear fuel performance codes to calculate behavior of the zirconium reactor core components in different regimes of operation. [ABSTRACT FROM AUTHOR]

Accident-tolerant fuel concepts have been developed recently in diverse research programs. Recent research has shown clear advantages of Cr-coated Zr cladding over bare cladding tubes regarding oxidation behavior under the design basis loss-of-coolant accident condition. However, limited data are available about the hydriding behavior of the Cr coating. For that purpose, Cr-coated Zricaloy-4 tubes were tested to investigate the effects of hydriding, oxidation, and postquench ductility behavior on coated Zr cladding. A high-power impulse magnetron sputtering (HiPIMS) process was used to produce a high-density coating on the Zircaloy-4 tube surface. Coated and uncoated Zircaloy-4 tube specimens underwent one-sided hydriding in a tube furnace filled with pure hydrogen gas at 425 °C. The tubing specimen ends were sealed with Swagelok plugs before the hydriding runs. For uncoated specimens, H analysis of the hydrided specimens indicated that the H content increased as the test time and initial pressure increased. However, almost no change was observed for the coated specimens that were hydrided under the same test conditions. After one-sided hydriding, the hydrided coated and uncoated specimens were exposed to steam at high temperatures for two-sided oxidation studies to simulate accident conditions. The coated specimens showed a slower oxidation: oxygen pickup was 50% lower than the uncoated specimens tested under the same conditions. Ring compression testing was performed to evaluate the embrittlement behavior of the Cr-coated specimens after hydriding and oxidation. The results indicated that the HiPIMS coating provides excellent protection from hydriding and oxidation at high temperatures. [ABSTRACT FROM AUTHOR]

The High Fluence Irradiation Facility at the University of Tokyo, which had provided a platform for dual-beam irradiation in Japan, was severely damaged by the 2011 earthquake. This paper reports a modification at this facility, i.e., installing a low-energy ion implanter instead of repairing the previous Van de Graaff accelerator. The platform of the dual-beam irradiation and/or s gas-ion beam irradiation was reconstructed, and the newly installed ion implanter was a stable, uniform, and high-density light element ion beam. The radiation-induced amorphization (RIA) behavior in Zr(Fe,Cr) 2 Laves phase was investigated in 180 keV-He+ beam irradiation to assess the performance of this ion implanter, and the irradiation temperature and dose-dependent RIA behavior were confirmed. Implying that this modification ensures the capability in terms of gas-ion beam irradiation and dual-beam irradiation in this facility, which will promote the research progress on radiation effects in nuclear material. [ABSTRACT FROM AUTHOR]

Zircaloy-2 is used in nuclear and biomedical industries therefore required high accuracy and precision, and achieved by application of electrical discharge machine (EDM). In this study, a new horizon of tool design is investigated for improvement in the performance of EDM. To measure the effect of tool design, Zircaloy-2 is machined with EDM using progressive Cu tool and measured the response parameters (MRR, TWR, radial overcut (Roc), radial undercut (Ruc), taper angle (Φ), and surface roughness). The progressive tool with varying design parameters of rake angle (0°, 45°, and 60°), flat land (2 mm), trunk diameters (10, 8, and 6 mm), and relief angle (0°, 45°, and 60°) are used to perform rough and finish machining in single EDM operation. MRR and SR are increased with increase in rake angle due to reduction in oxide and carbide deposition on the machined surface. Best combination for maximum MRR (1.131 × 10−3 mm3/min), minimum SR (4.313 µm), and minimum taper angle (2.17°) is obtained when machining is performed using T7. Multiresponse optimization (R-method) gives highest rank to progressive tool T7. Tool design improved TWR and significant reduction in radial overcut over conventional tool. [ABSTRACT FROM AUTHOR]

Cr-coated Zr alloys are widely considered the most promising accident-tolerant fuel (ATF) cladding materials for engineering applications in the near term. In this work, Cr coatings were prepared on the surfaces of 1400 mm long N36 cladding tubes using an industrial multiple arc source system. Orthogonal analyses were conducted to demonstrate the significance level of various process parameters influencing the characteristics of coatings (surface roughness, defects, crystal orientation, grain structure, etc.). The results show that the arc current mainly affects the coating deposition rate and the droplet particles on the surface or inside the coatings; however, the crystal preferred orientation and grain structure are more significantly influenced by the gas pressure and negative bias voltage, respectively. Then, the underlying mechanisms are carefully discussed. At last, a set of systemic methods to control the quality and microstructures of Cr coatings are summarized. [ABSTRACT FROM AUTHOR]

In this paper, the cladding of pure aluminum and a low-carbon steel alloy was performed through friction stir processing with minimal intermetallic compound formation. A 3 mm thick aluminum plate was clamped on top of a steel plate. A thick, pure copper plate was used as a backing plate. The tool pin length was adjusted to be the same as the upper plate's thickness (3 mm) and longer than 3.2 mm. The effect of the tool pin length and the rotation speed (500–1500 rpm) on the cladding's quality, microstructure, and the mechanical properties of the steel/aluminum interface were investigated using optical and scanning electron microscopy, a hardness test, and a peel test. The results showed that the bonding of pure aluminum and a low-carbon steel alloy can be successfully performed at a more than 500 rpm rotation speed. At a tool pin length of 3 mm and a rotation speed of 1000 rpm, sound and free-intermetallic compound–cladding interfaces were formed, while some Fel2Al5 intermetallics were formed when the rotation speed was increased to 1500 rpm. The pure copper backing plate has an essential role in eliminating or reducing the formation of intermetallic compounds in the cladding interface. When the tool pin length was increased to 3.2 mm, more steel fragments were found on the aluminum side. Moreover, with a higher rotation speed and longer tool pin length, more Fe2Al5 intermetallics were formed at the interface. Increasing the rotation speed and the pin tool length contributed to the enhancement of interface bonding. Meanwhile, the maximum tensile shear load was obtained at a rotation speed of 1500 rpm and a tool pin length of 3.2 mm. In addition, the hardness values of the interface were higher than the aluminum base metal for all the investigated samples. Decreasing the rotation speed and increasing the tool pin length can significantly increase hardness measurements. The average hardness increases from 42 HV of the pure aluminum to 143 HV at a rotation speed and a tool pin length of 1500 rpm and 3.2, respectively. [ABSTRACT FROM AUTHOR]

In the pressurized water reactor nuclear power plant, 316L SS chips were captured by the support grid and continued to affect the Zr-4 cladding tube, causing the fuel rods to wear and perforate. In this work, a 60° acute angle cone of 316L SS was used to simulate the cyclic impact of debris on a Zr-4 alloy tube with different initial impact velocities and impact angles. Results showed that increasing the initial impact velocity will generate a wear debris accumulation layer with a wear-reducing effect, but also promote the extension and expansion of fatigue cracks, resulting in the delamination of Zr-4 alloy tubes. The inclination of the impact angle increases the energy loss. The energy loss rate of the 45° impact is as high as 69.68%, of which 78% is generated by the impact-sliding stage. The normal force is mainly responsible for the wear removal and plastic deformation of Zr-4 alloy tubes. Tangential forces cause severe cutting in Zr-4 alloys and pushes the resulting wear debris away from the contact surfaces. [ABSTRACT FROM AUTHOR]