Zr-Nb Alloys Research Articles

Effect of annealing temperatures on microstructural stability and mechanical properties of Ti–Zr–Nb alloy

Due to its excellent deformability and high tensile strength, Ti–Zr–Nb alloy is promising in the field of aerospace and national defense. However, the relatively low stability of microstructure with temperature variation restricts its further application in navigation system. In this work, the microstructure evolution and mechanical properties of Ti–Zr–Nb alloy is investigated after an annealing treatment. When the annealing temperature increases, we observe the microstructure experiences recovery, recrystallization, reduction of dislocation density, refinement of α′-prime martensite phases and dissolution of ω-phases. These behaviors lead to the release of distortion energy, and thus the improvement of microstructural stability of Ti–Zr–Nb alloy. In the meantime, mechanical properties maintain after the enhancement of microstructural stability. Therefore, the propose annealing process can improve the microstructural stability and keep the good mechanical properties of Ti–Zr–Nb alloy in further aerospace application.

Formation of nanocrystalline γ-ZrH in Zr-Nb alloy: Crystal structure and twinning

In the present work, the lattice parameter and the twins of γ-ZrH hydride in Zr-2.5Nb-1Si were characterized using high resolution electron microscopy. The lattice parameters of γ-ZrH (P42/mmc, Zr2H2 unit cell) is determined to be a = 0.336 nm, c = 0.508 nm. Twinning γ-ZrH hydride ({011}<01̅1> type) is for the first time reported in zirconium alloys, whose orientation relationship with α-Zr is [100]γ-twins // [12̅10]α and (011)γ-twins // (0002)α. The formation process of γ-ZrH twins is also discussed based on a ‘grow-in’ mechanism during the transformation from α-Zr to γ-ZrH hydride.

Heat Resistance of Zr–1Nb Alloy Claddings in Water Vapor after Ion-Plasma Nitriding

Heat Resistance of Zr–1Nb Alloy Claddings in Water Vapor after Ion-Plasma Nitriding

Structure Effect on the Diffusion and Accumulation of Hydrogen in the Zr–1Nb Alloy

Structure Effect on the Diffusion and Accumulation of Hydrogen in the Zr–1Nb Alloy

Characterisation of AlCrCuFeMo x high entropy alloys for nuclear fuel cladding

High entropy alloys (HEAs) have great potential used for accident-tolerant fuel (ATF) due to their excellent properties. The ATF properties of AlCrCuFeMo x HEAs were systematically investigated. The AlCrCuFeMo x had the typical dendrite morphology and Cu and Al elements segregated in the interdendrite region. After 1200°C water vapour oxidation, compact and continuous α-Al2O3 oxide film formed on the surface and effectively protected the inner from further oxidation. When x = 1, the HEA had the best oxidation resistance (59 mg/dm2 weight gain after 1 h), two orders lower than that of the traditional Zr-1Nb alloy for nuclear fuel cladding. Under normal operation water condition, the performance of the present HEAs is not as good as Zr-1Nb due to the segregation of Cu and dispersed Al2O3 formed on the surface.

Mechanism and influence factors on energy-release capacity under the high-velocity impact fragmentation of Zr-Nb alloys

For investigating the mechanisms of microstructures and mechanical properties on energy-release capacity under high velocity impacting process of reactive structural materials (RSMs). Zr-Nb alloys with different Nb content were prepared via powder metallurgy. Both the α/β phase proportion and phase distribution vary with Nb content. The energy-release capacity under high-velocity impaction of Zr-Nb alloys shows an obvious difference. Micro-analyzing reveals that the smaller size of fragments after impaction is crucial for facilitating Zr reaction with oxygen, resulting in better energy-release capacity. However, the size of fragments after impaction is not only determined by the plasticity of alloys but also influenced by the microstructure. A continuous distribution of brittle α surrounding β is beneficial to controlling crack propagation path and forming fragments with small sizes. In the present work, the Zr-20 Nb alloy exhibits excellent energy-release capacity.

Molecular Dynamics Simulation of Nanoindentation of Nb-Zr Alloys with Different Zr Content

To understand the nanomechanical behaviors of the Nb-based alloys with Zr addition at room/high temperature, the molecular dynamics simulations of nanoindentation are conducted. In this work, the load-unload displacement curve, hardness, and dislocation characteristics of Nb-Zr alloys with varying Zr content ranging from 0 to 5 wt.% are studied. The simulation results are found to closely agree with the experimental one at 1 wt.%, therefore showing the reliability of the simulation. Moreover, considering distinct responses of alloys to different service temperature, the high-temperature nanoindentation are performed. The effects of Zr addition on the mechanical deformation under both temperatures are compared. The same phenomenon is found such that the optimum concentration range yielding the greatest hardness is 1–3 wt.%. The elastic modulus of NbZr alloy improves with elevated concentration at room temperature, while the hardness at higher temperature exhibits the opposite trend. This is attributed to the higher amplitude of atomic vibrations at high temperatures, which is more likely to deviate atoms from their equilibrium positions and weaken the pinning effect under external loading. Therefore, we believe that our studies on the nanomechanical mechanisms of materials at room/high temperature will provide an effective way for the alloying optimization design.

Oxidation of typical Zr-1 Nb alloy in high-temperature air under 700–900 °C

In order to promote the understanding of Zirconium alloy cladding failure under loss of coolant accidents (LOCA), air oxidation behavior of Zr-1 Nb-0.12 O (M5) alloy at 700–900 °C for 1–2 h was investigated. At different temperatures and times, m-ZrO2 was always the dominant phase of surface oxides, whereas oxide shapes, the integrity and roughness of oxide films differed noticeably. At 900 °C, M5 alloy exhibited accelerated kinetics and breakaway oxidation after approximately 80 min air exposure. The presence of ZrO and ZrO0.35 sub-oxides accounts for the high reaction activation energy (149.6 kJ/mol). During the kinetics acceleration, some intergranular cracks turned transgranular. The oxide/metal (O/M) interface became wavy, massive long transverse cracks and small radial cracks appeared in the oxide film, and pores distributed on the oxide layer and O/M interface. Air ingress through the oxide layer to initiate the matrix oxidation is jointly affected by air transport and ion diffusion.

Friction stir welding of Nb-1Zr alloy

• The Nb-1Zr Alloy joint was prepared by friction stir welding. • The Nb-1Zr alloy joint consists of SZ, TMAZ and BM. • The GDRX, DDRX, and CDRX are the operative mechanism for recrystallization during FSW of Nb-1Zr alloy. • SZ and TMAZ show higher hardness than BM in the Nb-1Zr alloy joints. Nb-1Zr alloy plates were successfully friction stir welded with the W-Re alloy tool for the first time. Geometric dynamic recrystallization (GDRX), discontinuous dynamic recrystallization (DDRX), and continuous dynamic recrystallization (CDRX) processes were observed on the welded joints. In addition, three different zones appeared in the joint: the base metal (BM), the stir zone (SZ), and the thermo-mechanically affected zone (TMAZ). No heat-affected zone (HAZ) is observed in the joint. With their refined grain size after welding, both welded zones (SZ and TMAZ) appeared to have considerably increased hardness compared to BM.

Diffusion bonding of Zr-2.5Nb zirconium alloy and 304L stainless steel with Nb/Ni hybrid interlayer

• Nb/Ni hybrid interlayer was applied to join 304L SS and Zr-2.5Nb Zr alloy. • The diffusion area has significantly stratified structure. • Ni 3 Nb IMCs occurred in the Nb/Ni interface with high hardness. Diffusion bonding of Zr-2.5Nb zirconium alloy and 304L stainless steel with Nb and Ni hybrid interlayer was performed at 850–1050 ℃ under 4 MPa for 30 min. From 304L side to Zr-2.5Nb side, the typical interfacial structure of the 304L/Ni/Nb/Zr-2.5Nb joints was. (Ni, Cr, Fe) solid solution/Ni/Ni 3 Nb IMCs/Nb/(Zr, Nb) solid solution. Of the five layers, the nano-hardness of Ni 3 Nb IMCs layer was the highest, reaching ∼9.22 GPa for the joint bonded at 1000 ℃. With the increase of bonding temperature, the shear strength of the joint increased first and then decreased, and the maximum strength of 84.4 MPa was obtained at 1000 ℃. For the joint bonded at 1000 ℃, the fracture location was between the residual Ni layer and Ni 3 Nb IMCs layer, and the fracture type was a mixture of brittle fracture and ductile fracture.

Designing hetero-structured ultra-strong and ductile Zr-2.5Nb alloys: Utilizing the grain size-dependent martensite transformation during quenching

• A heterogeneous structured Zr-2.5Nb alloys were fabricated successfully utilizing the grain size-dependent martensite transformation. • The present Zr-2.5Nb alloys manifest the highest yield strength (∼710 MPa), together with a high ultimate tensile strength (∼844 MPa) and good ductility (∼17.1%). • A model based on the grain-size-dependent critical resolved shear stress for dislocation slip and twinning has been proposed to explain the α' martensite substructures transition at a critical grain size d c = 3.3 μm. To further improve the service performance of Zr-2.5Nb alloy worked as pressure tubes in pressurized heavy water reactors, more investigation about the microstructure and thermomechanical processing route of Zr-2.5Nb alloy need to be conducted. In this work, a hetero-structured Zr-2.5Nb alloy was prepared by applying a novel technique. Microstructure analysis reveals that the alloy exhibits a grain size-dependent martensite substructure transition during post-rolling quenching. The hetero-structure consists of equiaxed primary α grains and the lamellae groups containing both parallel α' dislocation martensite and α' twin martensite. Compared with the previously reported Zr-Nb alloys, the present Zr-2.5Nb alloys manifest the highest yield strength (∼710 MPa), together with a high ultimate tensile strength (∼844 MPa) and good ductility (∼17.1%). The enhanced mechanical properties are found to arise from the properly controlled fraction/size of the two types of martensite, which not only significantly strengthens the alloy but also contributes to a stronger strain hardening. A model based on the grain-size-dependent critical resolved shear stress for dislocation slip and twinning has been proposed to explain the α' martensite substructures transition at a critical grain size d c = 3.3 μm. Below this size, the critical resolved shear stress (CRSS) for twinning is higher than that for the <c + a> slip. Thus, the α' dislocation martensite is more favorable to form. Otherwise, the α' twin martensite would exhibit a high activity. The present work indicates that making use of the grain size-dependent martensite transformation to tailor the hetero-structure in Zr alloys is an effective strategy to overcome the strength–ductility trade-off in the material.

Radial hydride fraction with various rod internal pressures and hydrogen contents for Zr-Nb alloy cladding tube

Hydride reorientation experiments for unirradiated Zr-Nb alloy cladding tubes under multi-axial stress states induced by internal pressurization were performed with peak cladding temperature set to 400 °C. Applied internal pressure was held constant during cooling down stage. PROPHET was used to analyze Radial Hydride Fraction (RHF) of tested cladding tubes. The attained RHF behavior for a wide range of rod internal pressure (7.5-18.5 MPa) and hydrogen content (0-1100 wppm) were investigated. Empirical models for RHF with respect to rod internal pressure and hydride contents were developed. Ring compression tests (RCTs) were conducted to investigate toughness (strain energy density) change with radial hydride formation. In order to take the multi-axial stress effect into account, rod internal pressure-based regulation is necessary. Hydride reorientation threshold rod internal pressure is ∼9.32 MPa. The rod internal pressure corresponding to hoop stress of 90 MPa is 11.5 MPa, indicating that hydride reorientation in multi-axially stressed Zircaloy cladding tube occurs at hoop stresses below 90 MPa. The presented thermodynamic model for threshold rod internal pressure gives improved agreement with experimentally measured threshold with input the directly measured orientation relationship between δ-hydride and α-Zr.

Studying the Hot Deformation Behavior of Zr-1Nb Alloy Using Processing Map and Kinetic Analysis

Studying the Hot Deformation Behavior of Zr-1Nb Alloy Using Processing Map and Kinetic Analysis

Change in the Crystallographic Texture of the Martensitic Phase in Superelastic Ti–Zr–Nb Alloys with Increasing Tensile Strain

Change in the Crystallographic Texture of the Martensitic Phase in Superelastic Ti–Zr–Nb Alloys with Increasing Tensile Strain

Isothermal experiments on steam oxidation of magnetron-sputtered chromium-coated zirconium alloy cladding at 1200 ℃

The isothermal steam oxidation behavior of chromium-coated zirconium alloy cladding at 1200 ℃ is studied. The cladding substrate is Zr-1 Nb alloy with outer diameter of 9.5 mm and thickness of 0.57 mm. The Cr coating is prepared by magnetron sputtering method with thickness of about 11 µm. The oxidation durations are 300 s~14,400 s. After oxidation, blisters are formed on the surface due to the compressive stress in coating, and the coating surfaces are porous or exhibit a morphology with ravines and granular crystals. A four-layer structure (Cr2O3, Cr, Zr(Cr,Fe)2 and Zr from outside to inside) is formed in the early stage of oxidation. However, Zr4+ can migrate into Cr coating through grain boundaries and reacts with Cr2O3. The redox reaction between Zr and Cr2O3 leads to the coating failure, resulting in the oxidation of Zr alloy substrate. Due to selective oxidation, a certain thickness of Cr coating is retained during the thickening of outer ZrO2. The emergence of outer ZrO2 layer is significantly delayed by Cr coating, and Cr coating is able to reduce the growth rate of outer ZrO2 layer. Therefore, Cr coating has a protective effect in 1,200 ℃ steam environment and can improve the oxidation resistance of Zr alloy cladding.

Compositional evolution of zirconium and niobium in the process of high-temperature nitridation of Zr–Nb alloys

The mechanism of formation of zirconium nitride-based ceramics in the single-stage high-temperature nitridation of Zr–Nb alloys with different niobium contents (0.1–10 at%) in a wide temperature range was determined using an oxidative constructing approach. In the process of nitridation, the segregation of a metallic niobium phase occurred with the subsequent formation of NbN. This should be taken into account when producing new high-temperature materials with unique functional properties

Influence of manufacturing processes on β-phase precipitates and corrosion properties of Zr-1Nb alloys

Zr-1Nb alloys manufactured by the alternate sequences between hot working and β-quenching were investigated in addition to an industry-fabricated Zr-1Nb material. Second phase particles, particularly composition and crystallography structure of β-phase precipitates, were characterized by electron microscopy. Pure steam corrosion test was performed to evaluate corrosion properties of the three Zr-1Nb alloys. Cross-sectional morphology and structure of the oxide films formed on the corroded alloys were analysed by scanning electron microscope and Raman spectroscopy. The results demonstrate strong effect of processing sequence on the β precipitates and corrosion properties. With the processing sequence of hot working and β-quenching, fine β-Nb particles are formed fully via precipitation from the Nb-supersaturated α-Zr grains, benefiting corrosion resistance. With the reverse sequence, the β phase and corrosion behavior are found dependent on hot working temperature in the phase regime of (α-Zr + β-Zr). Correlation between manufacturing processes and corrosion behavior is discussed in the light of second phase particles and oxides characterization.

Post-LOCA ductility assessment of Zr-Nb Alloy from 1100°C to 1300°C to explore variable peak cladding temperature and equivalent cladding reacted safety criteria

This study experimentally examines the variable PCT-ECR embrittlement criteria by conducting post-LOCA ductility assessments in the temperature range of 1100∼1300°C. Post-LOCA ductility assessments demonstrate the viability of variable PCT-ECR criteria, allowing either higher PCT for less oxidized specimens, or higher ECR limit for lower PCT specimens. The variable PCT-ECR criteria can be useful for high burnup fuel regulation. For potential burnup uprates that may lead to the violation of the current CP-ECR limit (18%) due to excessive steady-state oxidation, it may be possible to circumvent the regulation limit by allowing PCT less than the current limit (1204°C). This represents a new, yet more rational, safety envelop that may liberate nuclear reactor from sweeping conservatism associated with LOCA safety assessments. For the specimens oxidized at temperatures greater than 1200°C, ductile-brittle transitions take place even with substantially thicker prior-β layer (375 µm) and lower oxygen concentration compared to 1200°C specimens. As such, premature ductile to brittle transition occurs from the view point of oxygen uptake for steam annealing temperature above 1200°C. Premature embrittlement of 1250°C and 1300°C that cannot be explained in terms of the thickness of prior-β phase is relevant to promoted grain growth at elevated temperatures. Unlike lower temperature (≤1200°C), steam annealing temperature of 1250°C and 1300°C made grains continuously grow beyond the average grain size of 50 µm. The enhanced grain growth is considered to degrade cladding ductility as commonly observed in other HCP materials, in addition to solid-solution hardening of oxygen.

Identification of Relaxation Maxima of Internal Friction in Zr–Nb Alloy after Nitriding, Oxidation in Air, and In Situ Carburization

Identification of Relaxation Maxima of Internal Friction in Zr–Nb Alloy after Nitriding, Oxidation in Air, and In Situ Carburization

Effects of Ti content on the microstructure, mechanical properties and corrosion behavior of TixZrNb alloys

The study reports the effects of Ti content on microstructures, mechanical properties and corrosion behavior of the TixZrNb alloys. The BCC phase TixZrNb (x = 1, 1.5 and 2 mol) alloys have a typical dendritic morphology. With the increase of Ti content, the dendrite arms grow up, and the area of the inter-dendritic zone decreases. Furthermore, the segregation of Zr elements forms the βZr phase. Ti1ZrNb alloy has the highest yield strength of 516 MPa and hardness of 254 HV, and the Ti1.5ZrNb alloy shows the best elastic deformation performance (n = 0.46). The potentiodynamic polarization curve and electrochemical impedance spectroscopy show that Ti1.5ZrNb alloy has better electrochemical corrosion behavior than other alloys in 3.5 wt.% NaCl solution at 25 °C. The cyclic polarisation curve shows that Ti2ZrNb alloy is more prone to pitting corrosion in 3.5 wt.% NaCl solution.