Vanadium-base Alloys Research Articles

Characterization of irradiation-induced dislocation loops in Vanadium at 25-500 °C

Vanadium-based alloys have emerged as promising candidates for structural materials in fusion applications. However, as its base metal, the response of V to irradiation has received limited attention in prior studies. To gain a fundamental understanding of the irradiation damage in V, its microstructure evolution under 6 MeV Ti ion irradiation at 25–500 °C is investigated in the present study, with the focus on the detailed and comprehensive characterization of the behavior of the irradiation-introduced dislocation loops. Under room temperature irradiation, the “black dot” dislocation loops agglomerate linearly into rafts, during which their Burgers vectors are well aligned. With the temperature increases to 300 °C, the size of rafts increases and the density decreases, while the size of small loops maintains similar to the room temperature irradiation condition. As the irradiation temperature reaches 500 °C, the defects become highly mobile, resulting in the formation of extended dislocation loops or lines with hundreds of nanometers in size, with the rafts vanishing. All the observable loops under this irradiation temperature range exhibit the Burgers vectors of a/2 < 111>. All the loops observed in the displacement region are identified to be interstitial-type, while a small portion of loops observed in the diffusion region under elevated temperatures are vacancy-type.

Vanadium-based alloy for hydrogen storage: a review

Vanadium-based alloy for hydrogen storage: a review

Rational design of porous vanadium-based alloys modified with a Ni-Cu-Mo coating for alkaline water electrolysis

The development of a hydrogen evolution catalyst with both catalytic activity and stability is critical for hydrogen production from electrolytic water. Herein, a V-based porous alloy was prepared via high-energy ball milling and solid-state sintering. Then, the V-based porous alloy was modified with a Ni-Cu-Mo ternary alloy coating by direct current electrodeposition to obtain a composite hydrogen evolution cathode with high hydrogen evolution activity. The substrate has a certain hydrogen storage capacity combined with a high-activity Ni-Cu-Mo coating. The composite hydrogen evolution cathode exhibited high electrocatalytic activity toward the HER. It can afford a lower overpotential of 93 mV and a smaller Tafel slope of 97.4 mV/dec with a current density of 10 mA/cm2 in 1.0 M KOH. The composite hydrogen evolution cathode demonstrated outstanding stability after 2000 cycles and good durability after intermittent electrolysis for 20 h. Hydrogen protons can protect the components of the cathode composite from dissolution during discontinuous constant potential electrolysis. The composite hydrogen evolution cathode also exhibited a strong catalytic capacity for hydrogen evolution during intermittent electrolysis under alkaline conditions.

Experimental and theoretical insights into vanadium-based alloys for room temperature hydrogen storage on the example of Ti16Cr22Zr5V55-xFe2Mnx (x=0–3) alloys

In this work, the microstructures and hydrogen storage properties of the Ti16Zr5Cr22V55-xFe2Mnx (x =0, 1, 2, 3) hydrogen storage alloys were comprehensively investigated toward application under ambient conditions. The X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images of the alloys indicated that all of the alloys consist of a BCC main phase and a small amount of C14 Laves secondary phase. All of the studied alloys have a good activation performance and fast absorption/desorption kinetics at 298 K. The flatness of desorption plateau of alloy is improved by the tiny Mn introduction. With the increase of Mn content, the lattice parameter of BCC main phase, electron density and hydrogen absorption/desorption capacity decrease, and the desorption plateau pressure at 298 K increases in the range of 0.1–1 MPa. In addition, the essence of the dependence of high hydrogen capacity on electron density was revealed based on Fermi level. The Tilt, hysteresis, and width of plateau of PCT curve of vanadium-based alloys were clarified on the basis of Sievert's law. And a good quadratic fitting between desorption plateau pressure and Mn content was manifested.

The impact of vacancy formation energies on the nucleation and growth of helium (He) bubbles in low-activation multicomponent vanadium-based alloys

Generally, the complexity of concentrated solid solution alloys (CSAs) can effectively enhance their radiation tolerance. We studied the effect of helium (He) ion irradiation on body centered cubic (BCC) V, VCr, VCrFe and VCrFeMn alloys with the increase of complexity. The comparison shows the void swelling in terms of the size and density of bubbles in V, VCrFe and VCrFeMn decreases with the increase of the complexity after the same He ion irradiation. However, binary VCr alloy has the smallest void swelling although it has only two types of elements, that is less complexity, which is significantly different from VCrFe and VCrFeMn subjected to the same He ion irradiation. Meanwhile, the irradiated VCr lattice exhibits almost no shrinkage. First-principles calculations reveal that the high vacancy formation energy (VFE) of VCr could prevent He-vacancy clusters from absorbing vacancies to grow. The results suggest that the VFE could play a more important role in enhancing the radiation tolerance under He ion irradiation in addition to the compositional complexity.

Intrinsic mechanisms of superior hydrogen storage properties in V–Fe–Ti alloys: A combined experimental and theoretical study

Vanadium-based alloys have excellent reversible hydrogen storage properties, and the empirical lattice parameter law is often used experimentally for optimization of alloy composition. To reveal the underlying mechanisms, hydrogen storage properties and local environmental effect of H dissolution in V–Fe–Ti alloys were studied experimentally and computationally. The experimental results show that adding Fe and Ti has opposite effects on the hydrogen storage capacity of alloys, and (V85Fe15)100-xTix alloys with 20%Ti addition can exhibit the best performance, which satisfies the empirical lattice parameter law. Furthermore, atomic-scale simulations have demonstrated that H dissolution is affected by its dissolution location and surrounding alloy species through comparing the stability, electronic structure, and bonding characteristics of different V-based alloys. Besides, the correlation analyses of different factors with the hydrogen dissolution energy verify the rationality of the empirical law. Our findings provide useful insight into the rational design of Fe–V–Ti alloys for high-capacity hydrogen storage.

Microstructure and First Hydrogenation Properties of Ti16V60Cr24−xFex + 4 wt.% Zr Alloy for x = 0, 4, 8, 12, 16, 20, 24

In body-centered cubic (BCC) alloys of transition elements, elemental addition or substitution in the vanadium-based alloys can be beneficial for improving the hydrogen storage properties and for reducing the production cost. In this context, the current study focused on the effect of the substitution of Cr by Fe in Ti16V60Cr24−xFex + 4 wt.% Zr alloys where x = 0, 4, 8, 12, 16, 20, 24. The microstructure of each alloy was composed of a matrix having a chemical composition close to the nominal one and a Zr-rich region. From X-ray diffraction patterns, it was found that the matrix has a BCC structure, and the Zr-rich regions present the C14 Laves phase structure. The lattice parameter of BCC phases decreased linearly with x, in accordance with Vegard’s law. The measurement of the first hydrogenation at 298 K under 3 MPa of hydrogen revealed a decrease in the maximum hydrogen capacity: 3.8 wt.% for x = 0, 3.1 wt.% for x = 4 and around 2 wt.% for x = 8 to 24. The XRD patterns after hydrogenation showed a BCT phase for all alloys, with a C14 phase for x = 4, 8, 12 and with C14 and C15 for x = 16, 20 and 24.

Tailor-designed vanadium alloys for hydrogen storage in remote area and movable power supply systems

Vanadium-based alloys are potential materials for hydrogen storage applications in Remote Area Power Supply (RAPS) and Movable Power Supply (MPS). In this study, V80Ti8Cr12 alloys are tailor-made to meet the RAPS and MPS working conditions (293–323 K and 0.2–2 MPa). The effects of pulverization methods and particle sizes on the alloy's hydrogen storage properties have been systematically investigated. In addition, a novel Pressure-Composition-Isotherm approach is employed for the first time to accurately evaluate the hydrogen storage capacities. The reduction of particle size enhances the absorption kinetics due to the increased surface area. However, mechanical pulverization causes lattice distortion that decreases the hydrogen absorption capacity and desorption rate. In contrast, hydrogen embrittlement can effectively pulverize the alloys without generating lattice distortion. The results reveal that 5 mm sample, which is simply subjected to hydrogen embrittlement, achieves the largest usable hydrogen storage capacity up to 2.1 wt% and the fastest hydrogen desorption rate of ∼4 sccm/g that is nine times quicker than required for RAPS and MPS applications. After 500 cycles, the 5 mm alloy retains 90 % of its capacity, demonstrating excellent durability. Hence, 5 mm hydrogen-embrittled V80Ti8Cr12 alloy is an ideal hydrogen storage material in RAPS and MPS systems.

Microstructure, hydrogen permeability and ductile-to-brittle transition-hydrogen concentration of (V, Nb)-Ti-Co quaternary alloys

The ongoing development of hydrogen permeation alloys promotes the wide application of hydrogen energy, especially in the industry of hydrogen production from the water-gas shift reaction (WGS). However, before being widely used, it is still necessary to improve their comprehensive properties, such as hydrogen permeation flux and durability. Pd and its alloy membranes have been deeply studied and have appeared in the market in recent years. Vanadium-based alloys, as a new substitute for these palladium membranes, not only have lower cost but also higher hydrogen permeability. However, huge challenges remain-especially the poor mechanical stability and high susceptibility to hydrogen embrittlement (HE) which is closely related to high absorbed hydrogen concentration of Vanadium. To solve these problems, this paper investigated the structure, hydrogen diffusion, hydrogen dissolution, and hydrogen embrittlement properties of vanadium-based quaternary (V-Nb-Ti-Co) alloys. On this basis, the boundary of ductile brittle transition hydrogen concentration (DBTC) was described. It was found that new phases (such as Co2(V, Nb)3, Co7Nb6 etc.) will be formed in the structure when V is gradually replaced by Nb. Accordingly, the above changes the gradual substitution of V by Nb increased the hydrogen diffusivity and decreased hydrogen absorption. The overall effect is that the permeability decreases first and then increases, but larger hydrogen absorption will weaken the mechanical strength. As a result, the DBTC of the V-Nb-Ti-Co alloys shifts to the right somewhat (about 0.36 (H/M)), expanding the gap of the V-based single-phase alloys. This work demonstrated that the lower limit of DBTC can be adjusted by adding an appropriate amount of Nb in V-based alloys, thus simultaneously increasing the hydrogen permeability and hydrogen embrittlement resistance. This provides help and guidance for the design of novel hydrogen purification alloys.

Development of Fe-containing BCC hydrogen storage alloys with high vanadium concentration

Vanadium-based alloys are promising hydrogen storage materials which reversibly absorb hydrogen > 2.0 wt% under ambient conditions. In present study, we systematically investigated the V-Ti-Cr-Fe quaternary alloys with V concentration of 65–80 at% and discussed the relationship between hydrogen sorption properties and lattice parameter (a) and valence electron density (e/a). When 3.023 ≤ a ≤ 3.031 Å and e/a ≤ 5.12, the alloys show the hydrogen desorption amount ≥ 2.30 wt% and desorption plateau pressure ≥ 0.1 MPa at 298 K. More interestingly, compared to the Fe-free V75-Ti-Cr (Ti/Cr = 0.9) alloy, addition of 1–3 at% Fe could improve the hydrogen desorption amount and plateau pressure. The optimized alloy, V75-Ti-Cr-Fe2 (Ti/Cr = 0.9), shows a reversible hydrogen capacity of 2.46 wt% at 298 K in the 1st cycle and the capacity retention rate of 96 % after 100 cycles.

Analysis of Compositional Nuclear Transmutation Effects in Vanadium Alloys under Irradiation

The effects of nuclear transmutation in vanadium-based alloys under irradiation are considered in different reactor units including fast breeder reactors, such as (1) BOR-60 (experimental fast reactor), (2) EBR-II (experimental breeder reactor), and ITER (international thermonuclear experimental reactor). A comparison of nuclear transmutation rates for the analyzed [V–x% Cr(Ni)–y% Ti] alloys by data mining facilities is performed. It is demonstrated that the dominant types of interactions between neutrons and tested materials correlate with the level of thermalization in the neutron spectrum of a reactor, which has an effect on the value of nuclear transmutation rates to lead to distinctions in the resulting chemical composition of alloys after irradiation.

Study of Complex Effect of Intense Flows of Argon Ions and Pulsed Laser Radiation on Surface of Vanadium and Vanadium-Based Alloys (Review)

Study of Complex Effect of Intense Flows of Argon Ions and Pulsed Laser Radiation on Surface of Vanadium and Vanadium-Based Alloys (Review)

Impacts of Ce dopants on the hydrogen storage performance of Ti-Cr-V alloys

Vanadium-based alloys are considered to be one of the most promising hydrogen storage materials due to their high hydrogen storage capacity under ambient conditions. However, their complex activation at high temperature and poor stability pose serious challenges for large-scale applications. In this work, a series of TiCr3V16Cex (x = 0, 0.1, 0.2, 0.4, 1) hydrogen storage alloys were developed with different Ce contents using arc melting. The hydrogen storage and desorption performance, activation mechanism, and hydrogen absorption mechanism of the prepared alloys were investigated. Physical characterization confirms that the alloy is body-centered cubic (BCC) with Ce dopants, which exist in the form of oxides. The pressure-composition-temperature (PCT) test showed that the hydrogen storage plateau pressure of the Ce-doped alloy is increased compared to the Ce-free counterparts, while the hydrogen storage capacity decreased slightly with increasing Ce content. In addition, the influence of Ce doping on the alloy kinetics and thermodynamics is also discussed. The results showed that the TiCr3V16Cex (x = 0.2, 0.4, 1) alloys could absorb and release hydrogen at room temperature without activation. As an optimum, the TiCr3V16Ce0.2 alloy shows a hydrogen absorption rate of up to 3.69 wt%, and an effective hydrogen desorption capacity of 2.29 wt% at 25 °C. After hydrogen absorption and desorption cycles, the alloy almost maintains its original capacity. The Ce-doped BCC alloy developed in this work provides a new route to achieve high hydrogen storage performance under mild conditions.

Nanoscale microstructure and hydrogen storage performance of as cast La-containing V-based multicomponent alloys

Vanadium-based alloys (VBAs) occupy a prominent position in the field of hydrogen storage materials due to their many advantages, including the ability to absorb/desorb hydrogen with high capacity under moderate conditions. However, the kinetic and thermodynamic properties of these alloys must be improved to expand the range of their practical applications. In this work, we systematically studied the influence of La doping on the microstructure and hydrogen storage performance of multicomponent VBAs. It was found that the as-cast multicomponent V48Fe12Ti30Cr10 alloy prepared by arc melting contained micrometer/nanometer-sized crystals, which differed from the microstructure of traditional coarse-grained VBAs fabricated in the past decades. After the alloy was doped with La metal, its grains were refined into nanocrystallites with remarkable hydrogen absorption properties. This indicates that nanostructured VBAs can be realized by casting techniques, which is a traditional, low-cost, and engineering approach. The hydrogen storage capacity of the alloys first increased and then decreased with increasing La content. Furthermore, La doping considerably increased the alloy cycling stability. These findings can be used to develop novel hydrogen absorption materials for fuel cells with superior kinetic and thermodynamic properties.

Nanoscale microstructures and novel hydrogen storage performance of as cast V47Fe11Ti30Cr10RE2 (RE = La, Ce, Y, Sc) medium entropy alloys

As classical BCC structure solid state hydrogen storage materials, vanadium-based solid solution alloys occupied a prominent position in the field of hydrogen storage materials due to their significant advantages such as the ability to absorb and desorb hydrogen with high capacity under moderate conditions. In this paper, RE-containing medium entropy BCC solid solution alloys were designed. The microstructure, phase composition and hydrogen storage properties of the medium entropy alloys were systematically studied. Microstructural analysis showed that nanoscale crystals were found in as-cast medium entropy alloys obtained by arc melting followed by natural cooling inside the furnace. This is different from the vanadium-based alloys that are often regarded as traditional coarse-grained alloys in the past decades. The V 47 Fe 11 Ti 30 Cr 10 RE 2 alloys can be fully activated by one cycle of hydrogen ab/de-sorption after pretreatment. The kinetic test shows that the time required for the as-cast RE-containing medium entropy alloys hydrogen uptake to 90% saturation is less than 100 s at room temperature. The alloys exhibit very excellent hydrogen absorption kinetic properties than reported alloys takes at least about 300 s. This is due to the fact that the present alloys are composed of nanocrystals with numerous interfaces and grain boundaries, and these defects can act as good channels for the diffusion of hydrogen atoms. The V 47 Fe 11 Ti 30 Cr 10 Y 2 alloy exhibits a maximum capacity of 3.41 wt% at 295 K. The thermodynamics of hydrogen ab/de-sorption and the hydrogen desorption under non-isothermal conditions were also studied in detail. • Nanoscale crystals were found in as cast RE-containing medium entropy BCC solid solution alloys prepared by arc melting. • The alloys have numerous interfaces and grain boundaries. • The time required for the alloys hydrogen uptake to 90% saturation is less than 100 s.

Mechanical characterisation of V-4Cr-4Ti alloy: Tensile tests under high energy synchrotron diffraction

Vanadium base alloys represent potentially promising candidate structural materials for use in nuclear fusion reactors due to vanadium's low activity, high thermal strength, and good swelling resistance. In this work, the mechanical properties of the current frontrunner vanadium base alloy, V-4Cr-4Ti, have been interrogated using in-situ high energy X-ray diffraction (XRD) tensile testing at varying temperatures. The single crystal elastic constants of the samples were determined from the in-situ XRD data and used to evaluate results from density functional theory calculations. Polycrystalline elastic properties and Zener anisotropy were calculated from the single crystal elastic constants produced, revealing the effect of elevated temperature on the alloy's elastic properties. These results characterise important thermomechanical properties, valuable in mechanical modelling, that will allow further and improved analysis of the structural suitability of V-4Cr-4Ti ahead of alloy adoption in the mainstream.

Enhancing the phase stability of TiNi intermetallic compound via nanocrystallization in an irradiated multicomponent vanadium alloy

Intermetallic compounds often have a low radiation tolerance due to the low recombination rate of radiation-induced defects. In the present work, we designed a novel multicomponent vanadium-based alloy (MVA), V34Ti25Cr10Ni30Pd1, containing a micron-scale TiNi matrix phase with VCr nanoprecipitates (NPs) and a micron-scale VCr matrix phase with TiNi NPs. The MVA was irradiated with 6 MeV Ti3+ ions with a radiation dose of 5×1015ions/cm2 at room temperature. Results indicated that the micron-scale intermetallic TiNi matrix along with VCr NPs inside both became amorphous, while the micron-scale VCr matrix including numerous intermetallic TiNi NPs both exhibited a high structural stability after ion irradiation. The intermetallic TiNi matrix becomes amorphous due to the accumulation of radiation-induced defects, and the intermetallic TiNi NPs in VCr matrix have a high stability of crystallographic structure due to high-density interfaces between NPs and matrix. These results indicate that the phase stability of TiNi intermetallic compound is increased after nanocrystallization. Besides, the discrepancy of two matrix phases including precipitates after ion irradiation, and the underlying mechanisms are discussed in detail in this work. This work gives a guidance for designing new vanadium alloys and intermetallic compounds with enhanced structural stability under ion irradiation.

Micron-/nano-scale hierarchical structures and hydrogen storage mechanisms in a cast vanadium-based multicomponent alloy

Multicomponent vanadium-based alloys (MVAs), often considered as conventional coarse-grained alloys, have been extensively studied in past decades as important metal hydride electrodes and solid state hydrogen storage materials. A micron-scale microstructure composed of a V-based main phase and a TiNi-based secondary phase has been often used to explain the electrochemical performance of MVAs, where the micron-scale TiNi-based secondary phase with a three-dimensional network is considered as a catalyst for electrochemical reaction and/or a current collector. However, the atomic-scale microstructure of MVAs has been largely unknown to date. Here, using advanced aberration corrected electron microscopy, we have found micron-/nano-scale hierarchical structures in an as-cast MVA, V0.35Cr0.1Ti0.25Ni0.3. The micron-scale TiNi-phase contains VCr nanoprecipitates whereas the micron-scale VCr-phase contains TiNi nanoprecipitates and Ni-rich nanoclusters. In addition, we have found that the nanoprecipitates plays an essential role in the hydrogen storage, namely, TiNi nanoprecipitates with a diameter of approx. 30 nm absorb hydrogen faster than their VCr-matrix. Our studies revise conventional understanding on the microstructures in MVAs and the hydrogen storage mechanism, which may guide the development of nanostructured hydrogen storage materials for practical applications

Recent progress of vanadium-based alloys for fusion application

Recent progress of vanadium-based alloys for fusion application

The structure evolution of titanium–vacancy complex in a vanadium-based alloy

Under irradiation conditions, excess point defects interact strongly with the solute atoms in fusion reactor materials. The solutes can bind with point defects and form clusters such as solute–vacancy complexes. The evolution of these complexes at long timescale significantly influences the mechanical properties of the irradiated materials. In this study, we mainly use climbing image nudged elastic band method to investigate the evolution and migration of titanium–vacancy complexes in a vanadium-based alloy. The transition pathways associated with atomic trajectories of complex evolution in bulk and in grain boundary vicinity are calculated. Results show that both basin energies and transition barriers are affected when a complex is in grain boundary vicinity. The evolution is revealed to be driven by multiple titanium–vacancy interactions synergistically. The migration is supposed to be induced by two mechanisms: the vacancy reorientation jumps and complex dissociation–reformation which are both based on titanium–vacancy interactions. This research contributes to the understanding of solute diffusion and early-stage radiation defects in vanadium-based alloys.