Ni Zr Alloys Research Articles

Kinetic Study of the Formation Process of Ni-Zr Alloys

Kinetic Study of the Formation Process of Ni-Zr Alloys

Thermo-mechanical behavior of hypoeutectic Ni-Y-Zr alloys

Microstructure refinement and optimized alloying can improve metallic alloy performance: stable nanocrystalline (NC) alloys with immiscible second phases, e.g., Cu-Ta, are stronger than unstable NC alloys and their coarse-grained (CG) counterparts, but higher melting point matrices are needed. Hypoeutectic, CG Ni-Y-Zr alloys were produced via arc-melting to explore their potential as high-performance materials. Microstructures were studied to determine phases present, local composition and length scales, while heat treatments allowed investigating microstructural stability. Alloys had a stable, hierarchical microstructure with ∼250 nm ultrafine eutectic, ∼10 µm dendritic arm spacing and ∼1 mm grain size. Hardness and uniaxial compression tests revealed that mechanical properties of Ni-0.5Y-1.8Zr (in wt%) were comparable to Inconel 617 despite the small alloying additions, due to its hierarchical microstructure. Uniaxial compression at 600 °C showed that ternary alloys outperformed Ni-Zr and Ni-Y binary alloys in flow stress and hardening rates, which indicates that the Ni17Y2 phase was an effective reinforcement for the eutectic, which supplemented the matrix hardening due to increased solubility of Zr. Results suggest that ternary Ni-Y-Zr alloys hold significant promise for high temperature applications.

Features of formation of the Al–Ni–Zr system alloy structure obtained by reducing oxide compounds by aluminothermy using SHS metallurgy

This work is focused on establishing the regularity of the effect of zirconium (2.21; 3.29; 3.69 and 6.92 wt.% Zr) on structure formation, the nature of distribution of elements and the microhardness of structural components in the Al–Ni–Zr system alloys obtained by aluminothermy using the SHS metallurgy. Regularities of the formation of structural components and their microhardness depending on the content of zirconium in Al–Ni alloys (50 wt.%) have been identified and scientifically substantiated. Structural components were identified by the methods of electromicroscopic studies and X-ray microanalysis of elements. The structure of the initial alloy consists of Al3Ni2 (β′-phase) and Al3Ni nickel aluminides. Zirconium doping of the alloy in the amount of 2.21 wt.% leads to crystallization of zirconium nickel aluminide Al2(Ni,Zr). With further increase in the content of zirconium (more than 2.21 wt.% Zr), complex alloyed intermetallic compounds crystallize – Zr, W, Si aluminides and Ni zirconides. A regularity was established in the decrease of the solubility of nickel in nickel aluminides Al3Ni2 and Al3Ni and their microhardness as the zirconium content increases in the Al–Ni–Zr alloys from 2.21 to 6.92 wt.%. In nickel aluminide with zirconium Al2(Ni,Zr), this contributes to a decrease in the solubility of Ni, Al and increase in the concentration of Si and Zr. Zirconium doping of the Al–Ni alloy in the amount over 2.21 wt.% contributes to an increase in hardness (HRA), despite a decrease in the microhardness of the metal base (Al3Ni2, Al3Ni and Al2(Ni,Zr)). The main reason for increasing the hardness of the Al–Ni–Zr alloys is the crystallization of complex-alloyed intermetallides – Zr, W, Si aluminides and nickel zirconide, which probably have an increased microhardness. Thus, zirconium doping of the Al–Ni alloy makes it possible to obtain a plastic metal base from nickel aluminides Al3Ni2, Al3Ni and Al2(Ni,Zr) and complex-alloyed intermetallides with high hardness.

Regulating the microstructure and hydrogen storage properties of Ti23V40Mn37 + 10 wt% ZrNi alloys via ultrasonic treatment

To improve the activation performance and kinetic property of the Ti23V40Mn37 + 10 wt% ZrNi alloy, ultrasonic treatment was applied during its solidification. Besides, the effect of microstructure evolution on the hydrogen storage properties was investigated. Both as-cast and ultrasonically-treated (UST) Ti23V40Mn37 + 10 wt% ZrNi alloys were composed of BCC, C14 Laves and β-Zr phases. BCC phases appeared to be dendritic-shaped, of which the lattice parameter increased and the dendritic trunk was refined from 13.5 μm to 5.0 μm by ultrasonic processing. Hydrogen ab-/desorption rate accelerated and the maximum hydrogen desorption capacity was improved to 1.52 wt% at 303 K, owing to the increasing number of grain boundaries formed. The apparent dehydriding activation energy of the UST alloy decreased to 32.530 kJ/mol, while its dehydriding enthalpy (ΔH) enlarged to 40.22 kJ/mol H2 due to the lowered stability of the hydride.

Microstructural characteristics and self-accommodation of the martensite in equiatomic ZrPd and near-equiatomic NiZr alloys

Microstructural characteristics and self-accommodation of the martensite in equiatomic ZrPd and near-equiatomic NiZr alloys

New insights into the electrochemical and thermodynamic properties of AB-type ZrNi hydrogen storage alloys by native defects and H-doping: Computational experiments

In this study, we perform a computational experiment to inspect the impact of native Zr/Ni defects and H-doping atoms on the electrochemical and thermodynamic properties of the AB-type ZrNi alloys. The Korringa-Kohn-Rostoker (KKR) method integrated with the coherent potential approximation (CPA) was employed to execute the calculations. The results revealed that native Zr/Ni defects and hydrogen doping have a beneficial effect on the hydrogen storage properties of the studied compounds by decreasing the stability and decomposition temperature. In particular, we find that with an optimal concentration of native Zr/Ni defects and H-doping, the obtained values of the decomposition temperature are in accordance with the required values for the practical use of nickel-metal hydride (Ni-MH) batteries as a negative electrodes (253 to 318 K) as well as powering proton exchange membrane (PEM) fuel cells (289 to 393 K). Using the density of states (DOS), this decrease can be explained by the diminution of the number of Zr and Ni atoms that establish strong bonds with H atoms and by the shift of the total DOS toward the higher energies. The electrochemical capacity of Zr1-x-yNiH3+y and ZrNi1-x-yH3+y compounds increases to reach values of 550 and 540 mAh/g, respectively. These values are almost twice higher compared to the compounds currently used in the market based on the AB5-type alloy LaNi5 (300 mAh/g). These findings of enhanced electrochemical and thermodynamic properties could provide useful clues for the development of better ZrNi-based materials for Ni-MH batteries, PEM fuel cells and other related areas.

Evolution of local atomic structure accompanying devitrification of amorphous Ni-Zr alloy thin films

Thin film metallic glasses undergoing devitrification can form partially crystallized or fully crystallized materials with novel structural and magnetic properties. The development of desired and tunable properties of such systems drives the need to understand the mechanism of their thermal evolution at the atomic level. Co-sputtered amorphous Ni-Zr alloy thin films which were thermally annealed in steps of 200°C from room temperature up to 800°C, were observed to undergo an amorphous-to-crystalline transformation. Evolutions in local atomic structure, including oxide formation and depletion during this devitrification process, were determined using a combination of X-ray reflectivity (XRR), grazing incidence X-ray diffraction (GIXRD) and Extended X-ray Absorption Fine Structure (EXAFS) techniques. The most probable phase of the alloy was determined as Ni7Zr2; undergoing a polymorphous transformation. The slight oxide content in the films was also noted to decrease rapidly as annealing proceeded; leaving the crystallization pathway unhindered. modeling and analyses of XRR and GIXRD data showed that film thickness decreased with annealing while long range order increased. Pair distribution function peak widths were observed to decrease with annealing, indicating a control over structural disorder in the system as it transitioned from the amorphous to crystalline state. Partial atomic distribution in the environment of each constituent was examined at every stage of annealing through EXAFS measurements, which gave proper insight into atomic scale changes to the order present. Detailed analyses through these techniques gave coherent results, thus providing a true picture of the thermal evolution process of devitrification in this technologically useful material.

Cyclic Voltammetric Experiment-Simulation Comparisons of the Complex Zr4+ to Zr0 Reduction Mechanism at a Molybdenum Electrode in LiF-CaF2 Eutectic Molten Salt

Nuclear energy represents an important option for generating largely clean CO2-free electricity. Zirconium is a fission product in the nuclear reaction that needs to be extracted from irradiated fuels used in Gen-IV molten salt reactors. The present investigation addresses the electrochemical reduction of solution soluble Zr4+ (soln) to surface confined Zro (s−c) at a molybdenum electrode in a LiF—CaF2 eutectic molten salt at 840 °C using DC cyclic, square-wave and AC voltammetry. Cyclic voltammograms simulated by the reaction scheme: Zr4+ (soln) + 4e− → Zro (soln); Zro (soln) ↔ Zr*(s−c); Zr*(s−c) → Zr4+*(s−c) + 4e−; Zr4+*(s−c) → Zr4+ (soln); Zr*(s−c) + Zr4+ (soln) ↔ 2Zr2+ (soln); Zr2+ (soln) ↔ Zr2+*(s−c) and Zr2+*(s−c) → Zr4+*(s−c) + 2e− provided excellent agreement with experimental data over the scan rate range of 50 to 500 mV s−1. The interpretation of the simulation is that the reduction of Zr4+ (soln) to Zro (metal) takes place via a transiently soluble Zro (soln) in an overall 4-electron essentially reversible diffusion-controlled process having a reversible formal potential (Eo f) of −1.22 V (vs Pt). A minor oxidation process observed at −0.455 V (vs Pt) on the reversing the potential scan direction is simulated via the reaction step Zr(s−c) + Zr4+ (soln) ↔ 2Zr2+ (s−c) followed by Zr2+ (s−c) → Zr4+ (sol) + 2e−. The sharply rising initial component where reduction of Zr4+ (sol) commences, contains evidence of a nucleation-growth mechanism associated with the electrocrystallisation of zirconium metal. This initial rapid growth of current is not fully accommodated in the simulations, but all features found beyond the peak potential are supported by the theory. A comparison with theory based on a direct reduction of Zr4+ (soln) to the metallic state having unit activity is provided. It is proposed that an analogous mechanism applies at a Ni electrode, except that a Ni-Zr alloy formation occurs instead of Zr metal.

Amorphous Intergranular Film Effect on the Texture and Structural Evolution During Cold-Rolling of Nanocrystalline Ni–Zr Alloys

Amorphous Intergranular Film Effect on the Texture and Structural Evolution During Cold-Rolling of Nanocrystalline Ni–Zr Alloys

Thermodynamic mixing functions of the Fe–Ni–Zr liquid alloys

The mixing enthalpies of liquid Fe–Ni–Zr alloys were studied at 1873 K by means of a high-temperature isoperibolic calorimeter. The study was performed along the section xFe/xNi = 1/1 at xZr = 0–0.45. The limiting partial enthalpy of mixing of undercooled liquid zirconium in liquid Fe50Ni50 (at.%) alloy is (–139 ± 6) kJ⋅mol−1. The integral mixing enthalpy are negative over the investigated composition range. For the integral mixing enthalpy, an analytical expression was obtained by the least square fit of the experimental results and relevant literature data using the Redlich–Kister–Muggianu polynomial. The mixing thermodynamic functions of the Fe–Ni–Zr liquid alloys were modelled in the framework of the associate solution model.

Fe-X-B-Cu (X = Nb, NiZr) Alloys Produced by Mechanical Alloying: Influence of Milling Device

In this work, we analyze the influence of the milling device in the microstructural evolution of two Fe-X-B-Cu (X = Nb, NiZr) alloys produced by mechanical alloying (MA). The two milling devices are a planetary mil (P7) and a shaker mill (SPEX 8000). Microstructural analysis by X-ray diffraction detects the formation of a Fe rich solid solution. In the Fe-Nb-B-Cu alloy produced in the shaker mill also appears a Nb(B) minor phase, whereas in the Fe-NiZr-B-Cu alloy produced in the planetary mill, a minor disordered phase is formed. The comparative study regarding the energy transferred per unit of time in both devices determines that the shaker mill is more energetic. This fact explains that in the Fe-Nb-B-Cu alloy, Nb has not been introduced in the main Fe rich phase, whereas in the Fe-NiZr-B-Cu alloy milled in the shaker mill was formed the highly disordered phase. With regard to thermal analysis, the values of the apparent activation energies of the main crystallization process (above 200 kJ/mol) correspond to the crystalline growth of the nanocrystalline Fe rich phase.

Statistical learning for evaluation of crystal growth in low-melting alloy droplets with application to quasicrystal-forming Ti–Zr–Ni alloys

The evaluation of the crystal growth in undercooled alloy melts is essential for investigations of their solidification behavior. Low-melting alloy systems usually exhibit little self-illumination and cinematography is not often feasible. A time-temperature data based statistical learning approach is presented to evaluate the crystal growth in an undercooled droplet, where a spatial geometry-informed, errors-in-variables probabilistic model is developed based on the prediction of the dendrite growth paths. The preferable growth mechanism and growth velocities can be evaluated from statistical model selection and parameter estimation. Based only on the pyrometry data of two Ti–Zr–Ni alloys, a bulk growth mechanism is justified and the growth velocities in both the stable C14 phase and metastable icosahedral phase are able to be measured and statistically interpreted.

Effect of trace Ni addition on microstructure, mechanical and corrosion properties of the extruded Mg–Gd–Y–Zr–Ni alloys for dissoluble fracturing tools

Magnesium alloys, a novel functional material for the fabrication of fracturing tools, are being paid more and more attentions recently due to their relatively high mechanical properties and fast dissolubility ability after fracturing. In this study, the novel extruded Mg–10Gd–3Y–0.3Zr–xNi alloys will be reported and their microstructure, mechanical and corrosion behaviors will be also studied. The results show that Ni contents influence phase precipitation behaviors. With adding 0.2 wt% Ni, a large amount of Zr 7 Ni 10 phases will be precipitated insides α-Mg matrix, directly leading to degradation of strength and large corrosion rate. With further increasing Ni contents, the precipitation phases can be changed from Mg 5 RE to 18R-LPSO structure, resulting in higher mechanical properties and faster corrosion rate. Moreover, adding Ni element also change the texture orientation by influencing the precipitation behavior of the alloys. The alloys invented in this paper have attained the highest compressive and tensile properties among all the reported dissoluble magnesium alloys. This work is beneficial in understanding the role of Ni in the magnesium alloys and provides more materials alternatives for the fabrication of dissoluble fracturing tools.

Understanding the effects of hygrothermal aging on thermo-chemical behaviour of Zr-Ni based pyrotechnic delay composition

This study is aimed at understanding the aging effects related to heat and moisture on the pyrotechnic delay samples composed of zirconium-nickel (Zr-Ni) alloy as fuel and oxidants such as potassium perchlorate (KClO4) and barium chromate (BaCrO4). Naturally aged samples, thermally aged samples, and hygrothermally aged samples were considered in the thermal analysis using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), chemical analysis using x-ray photoelectron spectroscopy (XPS), and surface analysis using scanning electron microscope (SEM). High-speed photography was used to determine the ignition delay time and to observe the combustion behaviour of these samples. The numerical modelling on the reaction progress was performed, and the result indicated that heat accelerated the decomposition of KClO4 only, thereby promoting fast degradation of the performance of Zr component. Moisture, on the other hand, affected the decomposition of all KClOx (0 ≤ x ≤ 4) and degradation of the performance of both Zr and Ni components. Thus, moisture effect as opposed to heat was more prominent in the increased ignition delay time and subsequent ignition failure, which also induced surface cracks and overall oxidation of the metallic fuel, namely Zr-Ni alloy.

Influence of substrate bias voltage on structure and properties of DC magnetron sputtered Ni–Zr alloy thin films

Abstract

Structure refinement, mechanical properties and feasibility of deformation of hypereutectic Al–Fe–Zr and Al–Ni–Zr alloys subjected to ultrasonic melt processing

Hypereutectic Al–Fe and Al–Ni alloys offer a potentially attractive combination of properties, e.g. high-temperature strength and stability, high elastic modulus and low coefficient of thermal expansion. This potential, however, cannot be reached unless the structure of these alloys is refined so that their processing becomes possible. In this study, we for the first time apply ultrasonic melt processing for refining the structure of hypereutectic Al-4% Fe and Al-8% Ni alloys with 0.3 wt% Zr addition. Both primary Al3Fe and Al3Ni particles as well as aluminum/eutectic grains are significantly refined. It is suggested that cavitation-induced fragmentation of primary Al3Zr crystals plays a significant role in the nucleation of intermetallics as well as aluminum. Furthermore, the hardness and tensile properties of the alloys substantially increase after ultrasonic treatment due to the refined structure, which also contributes to the considerably enhanced ductility of the alloys. As a result, the fracture mode changes from brittle fracture to ductile fracture. The increase in ductility makes the alloys suitable for hot deformation, which is demonstrated by lab-scale hot rolling. In addition, precipitation hardening of the alloys can be achieved by high-temperature annealing at 450 °C due to retained Zr in the Al solid solution upon solidification. The results are supported by the analysis of the composition of a supersaturated solid solution of Zr in Al and scanning and transmission electron microscopy that confirms the precipitation of coherent Al3Zr nanoparticles. It is demonstrated that a combination of ultrasonic melt processing and alloying with Zr makes it feasible to develop new class of hypereutectic casting and wrought alloys based on the Al–Fe and Al–Ni systems.

Effect of Sn and Al additions on the microstructure and mechanical properties of amorphous Ti–Cu–Zr–Ni alloys**Project supported by the National Natural Science Foundation of China (Grant Nos. 51671161, U1806219, U1660108, and 51327901) and the Research Project of the Natural Science Foundation of Shanxi Province, China (Grant Nos. 2017JM5116 and 2020JZ-08).

Amorphous Ti–Cu–Zr–Ni alloys with minor addition of Sn and Al were prepared by melt spinning technique. The effects of Sn and Al additions on the microstructures and mechanical properties of glassy ribbons were investigated. The amorphous state of ribbons was confirmed by x-ray diffraction and transmission electron microscopy, where those ribbons with Sn addition exhibited a fully amorphous state. The characteristic temperature indicates that Ti45Cu35Zr10Ni5Sn5 alloy has a stronger glass-forming ability, as proven by differential scanning calorimetry. Ti45Cu35Zr10Ni5Al5 alloy showed a better hardness of 9.23 GPa and elastic modulus of 127.15 GPa and good wear resistance. Ti45Cu35Zr10Ni5Sn5 alloy displayed a pop-in event related to discrete plasticity according to nanoindentation. When the temperature is below 560 K, Ti45Cu35Zr10Ni5Sn5 alloy mainly exhibits elasticity. When the temperature rises between 717 K and 743 K, it shows a significant increase in elasticity but decrease in viscoelasticity after the ribbon experiences the main relaxation at 717 K. When the temperature is above 743 K, the ribbon shows viscoplasticity.

Zr segregation in Ni–Zr alloy: implication on deformation mechanism during shear loading and bending creep

Grain boundary (GB) migration and grain growth in nanocrystalline metals are major obstructions to exploit these materials to their fullest potential, thus limiting their utility as advanced structural materials. Here, we investigate the effect of Zr segregation to a Ni GB on migration and subsequent strengthening during shear deformation and high-temperature bending creep. Specifically, using molecular dynamics simulation, we simulate deformation of a Ni bicrystal specimen having a symmetric ∑5 grain boundary with and without segregated Zr. It is found that GB segregation up to 0.4 at.% pins the CSL boundary resulting in increased shear strength. Similar behavior is also observed in the case of bending creep deformation where the creep resistance increases only up to 0.4 at.%. This study indicates that larger amounts of GB segregation cause destabilization of the local atomic structure and consequently affect the GB stiffness. Moreover, we investigate the effect of Zr segregation on the interaction between the GB and a dislocation. We find that the preexisting dislocation is absorbed in the GB region for both clean and segregated specimens; however, the absorption path of the dislocation is different due to the change in GB stiffness caused by the Zr segregation.

Effect of direct-current operation on the electrochemical performance and structural evolution of Ni-YSZ electrodes

The effect of electrolysis operations on Ni-YSZ fuel electrode stability was studied at different current densities and fuel mixtures during 1000 h life tests. For a typical electrolysis mixture of 50% H2/50% H2O and 0.6 A cm−2 current density, cell ohmic resistance values were reasonably stable and no structural changes occurred. However, for more reducing conditions (97% H2/3% H2O), increasing the current density above 0.4 A cm−2 increased the ohmic resistance accompanied by significant electrolyte degradation including fracture and void formation at grain boundaries. Numerical analysis was carried out to determine the effective oxygen partial pressure across the electrolyte. The results show that the oxygen partial pressure values at high current density and low steam content may be low enough to reduce zirconia to form a Ni-Zr alloy product, initiating the observed electrolyte structural degradation.

Rapid solidification kinetics and mechanical property characteristics of Ni–Zr eutectic alloys processed under electromagnetic levitation state

The rapid solidification mechanism of Ni–Zr alloys was investigated by electromagnetic levitation (EML) technique assisted with high speed videography. A systematic analysis of the competitive growth mode between the primary phase and eutectic structure was conducted for three types of alloys (hypoeutectic Ni-5 at.%Zr, eutectic Ni-8.8 at.%Zr and hypereutectic Ni-13 at.%Zr alloys), whose maximum undercoolings reached up to 260, 192 and 270 K, respectively. With the increase of undercooling, the primary (Ni) phase of hypoeutectic Ni-5 at.% Zr alloy transferred from well-defined dendrites to dendrite fragments. Zr atom was difficult to diffuse into the Ni lattice because the radius of Zr atom was larger than Ni atom. For eutectic Ni-8.8 at.% Zr alloy, the competitive nucleation and growth between primary (Ni) phase and eutectics could happen when the undercooling exceeded 18 K. The refined dendrites of primary (Ni) phase and various eutectic morphologies were observed at the undercooling of 192 K. For the hypereutectic Ni-13 at.% Zr alloy, the growth morphology transition of the primary Ni5Zr intermetallic compound from faceted to non-faceted crystals occurred if the liquid alloy achieved a high undercooling. Furthermore, the atomic scale structure of the primary phase was explored by the transmission electron microscopy (TEM), which revealed that the solid solubility and the lattice constant were consistent at various undercoolings. Moreover, the compressive performance of these three type alloys were determined for EML solidified samples. Due to the effects of undercooling and composition on microstructures, Ni-5 at.%Zr and Ni-8.8 at.%Zr alloys exhibited plastic deformation at the large strain condition, while Ni-13 at.%Zr alloy showed brittle fracture feature. The compressive strength and yield strength displayed a non-linear relationship with the rise of undercooling.