Zr Alloy Research Articles

Mechanical property and cracking mechanism of Cr-coated Zr alloy under tensile and compressive loading

Cr coatings are considered as the most promising candidate materials for accident-tolerant fuel cladding coatings. In combination with optical microscopy, focus ion beam, energy dispersive spectrum and universal testing machine, the effect of Cr coating on hoop tensile and compressive mechanical properties of Zr alloy was studied and the underlying cracking failure mechanism of Cr coating was revealed. The results indicate that Cr coating slightly increases tensile/compressive yield strength and tensile strength compared with those of uncoated Zr alloy. This is attributed to high hardness/elastic modulus of Cr coating. Interrupted hoop tensile and compressive tests show that Cr coating cracking concentrates in the range of 0-30°. Further, crack initiation of the coating occurs either at the surface or at the interface between Cr coating and the matrix. Compared with the former, the latter is dominant cracking mode, irrespective of tensile and compressive loading. In lights of the advanced microstructural analysis, one possible reason, i.e., the existence of nano-scaled Al-enriched loose layer between the interface, in which nano-cracks and voids exist, is proposed to explain the interfacial cracking. The result indicates that the optimization of the interfaces can improve the resistance of coating failure. In addition, crystallographic study demonstrates that the crack propagation in the Cr coating is along the high-angle grain boundaries with the misorientation of 50°.

Microstructures and mechanical properties of a novel Al-5Mg-3Zn alloy with the combined additions Sc and Zr

The study investigated the impact of Sc and co-addition of Sc and Zr on the dispersoids, subsequent grain structures and aging precipitations, and the ultimate mechanical properties of Al-5Mg-3Zn-xSc-yZr (x + y = 0.2wt.%) alloys were studied. The results indicate that the co-addition of Sc and Zr produces the highest number density of dispersoids among the three alloys. The Al-5Mg-3Zn alloy mainly comprises fully recrystallized equiaxial grains (close to 100%) after solution treatment. In contrast, the recrystallization ratio of Al-5Mg-3Zn-0.1Sc-0.1Zr remarkably decreases to 9% owing to the presence of fine and dense Al3M dispersoids to impede the mobility of sub-grain boundaries. Adding the Sc element alone reduces the number density of the T-Mg32(Al, Zn)49 and enhances their size during the subsequent aging treatment, while the co-addition of Sc and Zr elements shows an opposite trend. The primary factor contributing to this result is that the microalloying of Sc and co-addition of Sc and Zr affects the diffusion of Mg and Zn solute atoms in Al-5Mg-3Zn alloys. Consequently, the peak-aged Al-5Mg-3Zn-0.1Sc-0.1Zr alloys exhibit a yield strength of 481MPa, an ultimate tensile strength of 547MPa, and an elongation of 12%, which is superior to the reported Al-5Mg-3Zn alloys. The good strength-ductility synergy can be attributed to the combination of a high number density of dispersions, grain refinement, and high-volume fraction nanoprecipitates.

Evolution of microstructure, texture, and mechanical performance of Mg-13Gd-2Er-0.3Zr alloy by double extrusion at different temperatures

Evolution of microstructure, texture, and mechanical performance of Mg-13Gd-2Er-0.3Zr alloy by double extrusion at different temperatures

A Nonconventional Method to Produce Zr Alloys to Study the Fe23Zr6 Intermetallic Compound in the Fe-Zr System

A Nonconventional Method to Produce Zr Alloys to Study the Fe23Zr6 Intermetallic Compound in the Fe-Zr System

Microstructure, electrical resistivity, and tensile properties of neutron-irradiated Cu–Cr–Nb–Zr

High strength, high conductivity copper alloys that can resist creep at high temperatures are one of the primary candidates for efficient heat exchangers in fusion reactors. Cu–Cr–Nb–Zr (CCNZ) alloys, which were designed to improve the strength and creep life of ITER Cu–Cr–Zr (CCZ) reference alloys, have been found to have comparable electrical conductivity and tensile properties to CCZ alloys. The measured creep rupture times for these improved alloys is about ten times higher than the ITER reference alloys at 90–125 MPa at 500 °C. However, the effects of neutron irradiation on these alloys, and the ensuing material properties, have not been studied; thus, their utility in a fusion reactor environment is not well understood. This study characterizes the room temperature mechanical and electrical properties of a neutron-irradiated CCNZ alloy and compares them to a neutron-irradiated ITER reference heat sink CCZ alloy. Tensile specimens were neutron irradiated in the High Flux Isotope Reactor (HFIR) to 5 dpa between 250 °C and 325 °C. Post-irradiation characterization included electrical resistivity measurements, hardness, and tensile tests. Microstructural evaluation used scanning electron microscopy, energy dispersive x-ray spectroscopy, and atom probe tomography to characterize the irradiation-produced changes in the microstructure and investigate the mechanistic processes leading to post-irradiation properties. Transmutation calculations were validated with composition measurements from atom probe data and used to calculate contributions to the increased electrical resistivity measured after irradiation. Comparisons with CCZ alloys in the same irradiation heat found that the post-irradiated CCNZ and CCZ alloys had comparable electrical resistivity. Although CCNZ alloys suffered more irradiation hardening than CCZ, the overall tensile behavior deviated very little from non-irradiated values in the temperature range studied.

Coupled CA-FE Simulation for Dynamic Recrystallization of Mg-8Gd-4Sm-1Zn-0.5Zr Alloy During Hot Compression Deformation

Coupled CA-FE Simulation for Dynamic Recrystallization of Mg-8Gd-4Sm-1Zn-0.5Zr Alloy During Hot Compression Deformation

Numerical investigation on boiling crisis characteristic of a 7-rod HCF assembly in hexagonal lattice

Helical cruciform fuel (HCF) has the advantages of larger heat transfer area, enhanced coolant mixing and self-supporting, which contribute to increasing power density and safety margins. Compared with the square lattice configuration, the hexagonal arrangement of HCF assembly is more compact, which can help achieve a higher power density. In this paper, the flow characteristics and heat transfer behaviors of HCF in hexagonal lattice were predicted at high and low vapor quality during boiling crisis based on Eulerian two-fluid model. The influence of twist pitches and cross-sections of the fuel rod on heat transfer efficiency and fuel temperature was also studied. The cross-flow intensity changed periodically with a 30° cycle at low vapor quality, and did not fluctuate periodically at high vapor quality, which decreased with the increase of flow resistance. The highest heat flux of HCF rod was the at the blade root and the lowest was at the blade tip, and the maximum to average heat flux ratio was about 1.8. The peak vapor fraction and temperature occurred at leeside side of the fuel rods. The increase of the twist pitch reduced the critical heat flux (CHF), and the increase of blade length enhanced the non-uniformity of heat flux distribution. During boiling crisis, the maximum temperature of the fuel was lower than the phase transition temperature of U-50 wt%Zr alloy, which means the cladding meltdown caused by boiling crisis will occur before phase transition of the fuel.

Atom probe tomography of deuterium-charged optimised ZIRLO

AbstractThis study investigates the morphology and composition of hydrides in Optimized ZIRLO following electrochemical deuterium charging. Both ZrO and ZrDx phases were formed upon charging. The interfaces between these phases are investigated by using atom probe tomography aided by cryogenic sample transfer. The Ga and Sn have formed a “net”-like structure at the original atom probe specimen surface, which is assumed to be associated with the boundaries between individual hydride laths/needles, as it thought to have formed as these species were excluded from the hydrides. Calculation of the D/Zr ratio throughout the sample allows for identification of the ZrDx phases, revealing the specimen consists of a complex arrangement of different hydride phases. In some areas there is small excess of D in the hydride, i.e. ZrD2+y. This result is interpreted as deuterium which was “frozen” as it was passing through the hydride during electrochemical charging. The observed microstructural changes and interfacial phenomena contribute valuable insights that may prove useful for improving the performance and safety of Zr alloys.

Unveiling the interaction between corrosion products and oxygen reduction on the corrosion of Mg–4Nd–0.4Zr alloy under thin electrolyte layers

Although hydrogen evolution reaction (HER) is considered to be the main cathodic reaction of Mg corrosion, oxygen reduction reaction (ORR) has been recently confirmed to be a secondary cathodic reaction. The factors affecting ORR of magnesium (Mg) alloys are still unclear, especially in cases under thin electrolyte layers (TEL). In this work, the influence of the corrosion product films on the cathodic reactions of Mg alloys under TEL and in a bulk solution was investigated. ORR does not influence the hydrogen evolution rates in the corrosion of Mg alloys. Therefore, with the existence of oxygen, corrosion rates of Mg alloys measured by hydrogen evolution tests are not accurate under TEL. And weight loss test is a more accurate method to evaluate Mg corrosion rates under TEL. ORR was confirmed to participate in the corrosion of Mg–4Nd–0.4Zr, Mg–4Nd and Mg–0.4Zr alloys under TEL. In 100-μm TEL, the highest contribution of ORR in cathodic reactions for the corrosion of Mg–4Nd–0.4Zr, Mg–4Nd and Mg–0.4Zr alloys are 28.6%, 39.1%, and 35.8%, respectively. The more protective film on Mg–4Nd–0.4Zr alloy provides a stronger inhibition effect against the diffusion of oxygen, leading to decreased ORR contribution in cathodic reactions. In addition, it is suggested that the preparation of Mg alloys with protective corrosion product films can inhibit the corrosion induced by ORR in the atmosphere. This work emphasizes the effects of corrosion product films on ORR in Mg corrosion, especially under TEL.

Achieving high strength-ductility synergy in Mg-Gd-Zn-Zr alloy by controlling extrusion processes parameters

The high rare earth content in current magnesium alloys poses environmental and economic challenges. To address this issue, this study designs a Mg-7.5Gd-6Zn-0.5Zr alloy (GZ76, wt.%) with low rare earth content, high strength, and excellent ductility. The morphology of the as-cast GZ76 alloy is characterized by a dendritic structure consisting of an α-Mg matrix and interdendritic zones comprising W+I phases, interspersed with fragmentary Zn-Zr phases. Furthermore, the extrusion process is employed to meticulously control the microstructure and enhance the mechanical properties of the alloy. This research focuses on investigating the effects of extrusion parameters on magnesium alloys to optimize their extrusion processing conditions. Through systematic manipulation of the extrusion ratio and extrusion speed, a comprehensive analysis is conducted to examine their impacts on grain refinement, texture evolution, distribution of second phase, and mechanical properties of extruded magnesium alloys. The results indicate that due to the insufficient recrystallization process, the microstructure of the as-extruded GZ76 alloys exhibits a bimodal structure, encompassing both fine recrystallized grains and coarse unrecrystallized grains. At larger extrusion ratio, a faster extrusion speed leads to superior mechanical properties of the alloy. Conversely, at smaller extrusion ratio, a slower extrusion speed is more favorable for achieving higher strength. These findings provide valuable insights into optimizing the extrusion parameters for enhancing the performance of magnesium alloys in engineering applications.

HTXRD based lattice thermal expansion and specific heat capacity modelling of C15-Fe2Zr Laves phase

Crystallographic phase pure C15-Fe2Zr was obtained through arc melting technique. X-ray Diffraction (XRD), scanning electron microscope (FESEM) along with energy-dispersive X-ray analysis (EDS) and differential scanning calorimetry (DSC)were employed to study the single phase in Fe-33.3at.% Zr alloy. Rietveld refinement of the high-temperature XRD patterns (from 298K-873 K) revealed the average linear and volumetric coefficients of thermal expansion of the alloys as αai= 0.3643 × 10−5 K−1 and αVi = 1.0916 × 10−5 K−1, respectively. The experimental heat capacity and enthalpy increment of the C15-Fe2Zr phase from 310K to 890K was modelled employing Quasi-harmonic Debye Grüneisen theoretical modelling by identifying the vibrational, electronic, anharmonic and magnetic contributions. Curie temperature(~625K) was determined from the magnetic contribution of the heat capacity.

Anisotropic stress corrosion cracking susceptibility of Mg-8Gd-3Y-0.5Zr alloy

This study investigates the stress corrosion cracking (SCC) behavior of a Mg-8Gd-3Y-0.5Zr alloy in a 3.5 wt.% NaCl solution using slow strain rate tensile (SSRT) testing. The results reveal that SCC susceptibility increases as the strain rate decreases, with hydrogen embrittlement (HE) becoming more dominant at lower strain rates, leading to brittle fracture. Anodic dissolution (AD) plays a more significant role at higher strain rates, resulting in mixed fracture modes. Additionally, the mechanical properties and SCC resistance are strongly influenced by the sample orientation. TD-oriented samples show higher SCC susceptibility than RD-oriented ones due to the alignment of Gd- and Y-rich precipitates and grain boundaries, which act as initiation sites for SCC. These precipitates form micro-galvanic couples with the Mg matrix, accelerating localized corrosion and HE. The findings provide insights into the SCC mechanisms of VW83 alloy and highlight the importance of optimizing microstructure and processing conditions to improve its corrosion resistance.

Microstructure and mechanical performance of cold spray Cr coatings

Cold spray deposition has emerged as a promising method for applying protective coatings in the nuclear industry, particularly for enhancing the accident tolerance of fuel assemblies. In this process, helium gas is often used to propel solid powder particles towards the target substrate, however, nitrogen gas is also considered due to its significantly lower cost. In this study, we investigate the influence of nitrogen and helium gas as propellants on the properties and microstructure of pure chromium (Cr) coatings on zirconium (Zr) alloy cladding tubes. Employing Scanning Electron Microscopy (SEM) and electron and x-ray diffraction techniques (EBSD, XRD), we explore the structural characteristics of the coatings. Additionally, in-situ SEM tensile testing at room temperature, coupled with Digital Image Correlation (DIC), is utilized to assess the coating cracking behaviour. Our findings reveal distinct differences in coating morphology and residual stress between nitrogen and helium propelled Cr coatings. The nitrogen-propelled coating exhibits a more porous structure with smoother coating/substrate interfaces and lower compressive residual stress compared to the helium-propelled one. This results in earlier strain-induced crack initiation and higher crack density at lower strains (0.5–2%). However, at higher strains (2–5%), both coatings demonstrate identical crack saturation densities (saturated number of cracks per unit length), accompanied by similar crack toughening mechanisms and evidence of shear strain bands at intercrack regions, indicative of plasticity onset.

The oxidation-dissolution behavior of Cr-coated Zr alloy in high temperature water

The corrosion and dissolution behavior of Cr-coated Zr alloy were investigated in high temperature water under varying dissolved oxygen (DO) and temperatures. Results demonstrate that the oxidation and dissolution rates of Cr coatings increase significantly with higher DO levels and temperature, while the Zr substrate remains unaffected by DO concentration. At DO levels below 10 ppb, Cr coatings exhibit high stability, but at 300 ppb DO, rapid corrosion/dissolution and spallation occur. The electrochemical potential (ECP) shifts in response to temperature and DO, driving the dissolution mechanism through three distinct region: steady-state, field-assisted dissolution (FAD), and complete dissolution. During the FAD period, a porous nanocrystalline Cr2O3 layer with residual Cr forms, characterized by non-uniform dissolution due to preferential oxidation at grain boundaries and microstructural defects. The soluble HCrO4− ions form at the base of the porous layer, followed by partial recrystallization at the surface, leading to the development of a thin Cr2O3 crystalline layer.

Multiscale-informed irradiation growth model of Zr-Sn-Nb alloys

A systematic multiscale-informed model is developed to predict the irradiation growth behavior of Zr-Sn-Nb alloys, which considers the anisotropy and temperature dependence of both plasticity and irradiation, as well as the alloying effect of Zr alloys. This model consists of a cluster dynamics submodel to consider the kinetics of irradiation defect, an alloying effect submodel informed by atomic simulations and experiments, a microstructure transition submodel derived from discrete dislocation dynamics, and a continuous irradiation growth submodel based on crystal plasticity. It effectively captures the irradiation-induced coevolution of multiple microstructures, including point defects, mobile clusters, dislocation lines and irradiation loops on the prismatic and basal plane, as well as Nb-induced precipitates. It is suitable for high-dose irradiation conditions as it reasonably considers the transition from high-density irradiation loops to tangled dislocation network. The predicted irradiation growth strain, as well as the density and size of irradiation loops, are in good agreement with almost all the available experiments for pure Zr, Zr-Sn, Zr- Nb, and Zr-Sn-Nb alloys at different irradiation doses in the temperature range of 473 - 673 K. This work is hoped to provide a powerful tool for developing irradiation resistance cladding materials.

Microstructure evolution and high temperature air oxidation behaviour of thick Cr coatings at 1200°C

The thick Cr coated Zr-4 alloys were prepared by magnetron sputtering deposition and their microstructure evolution and high-temperature air oxidation behaviour were investigated. Oxidation tests showed that the thick Cr coatings can improve the high-temperature air oxidation resistance of Zr-4 alloy even if the α-Zr(O) layer was formed at some regions. The mechanism of high-temperature air oxidation was also discussed in detail, and these experimental results could provide data for establishing a reliable prediction model of this degradation.

Influence of re-melting rate on the dry sliding wear characteristics of LPBFed Cu–Cr–Zr alloy

For the past few decades, Copper alloys have made significant contributions to a variety of industrial applications due to their efficient electrical and thermal conductivity. However, moving mechanical assemblies continues to raise concerns about wear-related mechanical breakdowns on a worldwide scale. Hence, this research focuses on examining the wear parameters such as load, sliding velocity and distance based on the re-melting strategy of the (Laser Powder Bed Fusion) LPBF process. The sliding tests were carried out over a wide range load (15, 25, 35 and 45 N), sliding velocity (1, 1.5, 2 and 2.5 m/s) and sliding distance (1500, 2500, 3500 and 4500 m) with a pin-on-disc configuration. The LPBFed Cu–Cr–Zr alloy coupon was printed with four different re-melting ranges (5, 15, 30 and 45%) and it was explored to minimise the occurrence of un-melted particles and inter-particle gaps. The wear results show that the wear parameters have a positive correlation with the Wear Rate (WR) and co-efficient of friction (COF) and also witnessed that the WR and COF decrease with increasing the re-melting rate. The nano-hardness analysis was compared on the un-melted and spattered particles and the re-melted surface. The results show that the spattered particles possess 35.8% more nano-hardness than the other surface on the Cu alloy coupon printed with a 45% re-melting range. The FE-SEM images of the worn-out surface reveal that un-melted and spattered particles have a major contribution in reducing the wear resistance of the printed Cu alloy coupons.

New insights into physical origins of dynamic strain aging in Ti-2Al-2.5Zr alloy and influence on LCF and HCF behaviors

The multi-step strain aging tests were meticulously designed in this work to reveal the physical mechanisms of static strain aging (SSA) and dynamic strain aging (DSA) behaviors in Ti-2Al-2.5Zr alloy for the first time. It was revealed that the shuffling mechanism of interstitial oxygen atoms combined with the pinning effect of locally-generated cross-slip on the movement of screw dislocations were responsible for the occurrence of strain aging. Furthermore, the effects of DSA on the low-cycle fatigue (LCF) and high-cycle fatigue (HCF) properties were elucidated in Ti-2Al-2.5Zr alloy. Results showed that the sensitivity of DSA to cyclic loading was attributed to the generation of numerous residual edge dislocation segments through local cross-slip, facilitating the formation of dislocation veins which inhibited the formation of persistent slip bands (PSBs) and led to the significantly cyclic hardening. Finally, it was emphasized that the phenomenon of DSA should be carefully considered for the structural integrity assessment of Ti-2Al-2.5Zr alloy and several suggestions were provided.

Mechanical and high-temperature steam oxidation properties of Cr coatings deposited via high-power impulse magnetron sputtering

Applying protective coatings to Zr alloy cladding surfaces is one of the better methods to design fuel tolerant materials. In this study, the surface of a Zr-4 alloy was coated with Cr using high-power impulse magnetron sputtering. Furthermore, the mechanisms by which bias voltages affect the mechanical characteristics, resistance to high-temperature steam oxidation, and coating structure were elucidated. The coating exhibits a strong (200) weave structure with coarse grains at a bias voltage of -100 V. With increasing bias, the energy of deposited particles increases, grains continue to grow, (200) preferential growth orientation disappears, and the coating exhibits a (110) crystal orientation. The growth structure of the coating first shows a tendency to be dense and then loose. For the Cr coating with a (200) crystal orientation, a dense oxide layer is preferentially formed after oxidation, which can effectively block the internal diffusion of O. With increasing oxidation time, coarse Cr grains can effectively block the external diffusion of Zr. Furthermore, the Cr coating exhibiting a (110) crystal orientation was severely oxidized after oxidation, resulting in the formation of cracks at the film base; this accelerated the outward diffusion of Zr.

Role of Mo and Zr Additions in Enhancing the Behavior of New Ti–Mo Alloys for Implant Materials

AbstractThe utilization of Ti–Mo alloys in biomedical applications has gained attention for use in biomedical applications owing to their non-toxicity, reasonable cost, and favorable properties. In the present study, Ti–12Mo–6Zr and Ti–15Mo–6Zr alloys were prepared using elemental blend and mechanical alloying techniques. The effect of alloying elements Mo and Zr of Ti–Mo alloy, as well as the effect of fabrication techniques of Ti–Mo–Zr trinary alloys, were investigated. Thermodynamic calculations supported by CALPHAD analysis revealed that the addition of Zr increases lattice distortion, which contributes to enhancing the strength. Conversely, adding Mo decreases the enthalpy, facilitating improved mixing and solid solution formation. The as-sintered samples were characterized by X-ray diffraction, optical microscope, and scanning electron microscopy, and their microhardness, compressive, and corrosion behavior were investigated. Among all the investigated alloys, Ti–15Mo–6Zr alloy prepared by the mechanical alloying technique, milled for six hours at 300 rpm, compacted at 600 MPa, and sintered at 1250 ℃, shows good comprehensive mechanical properties with a preferable compressive strength (− 1710 MPa) and hardness (396 HV5), as well as the lowest wear rate (0.69%) and corrosion rate (0.557 × 10–3 mm/year). This can be related to the solid solution strengthening and relative density, together with dispersion and precipitation strengthening of the α phase. Remarkably, the combination of high mechanical and corrosion properties can be achieved by tailoring the content of the α phase, controlling the density, and providing new fabricating techniques for β Ti alloys. Graphical Abstract