Vanadium Alloys Research Articles

Multilayer “Steel/Vanadium Alloy/Steel” Hybrid Material Obtained by High-Pressure Torsion at Different Temperatures

The severe plastic deformation (SPD) method for joining dissimilar metal materials to obtain a multilayer hybrid material having an ultrafine or nanoscale structure was proposed. A nanostructured multilayer “0.08C-18Cr-0.5Ti steel/V-10Ti-5Cr alloy/0.08C-18Cr-0.5Ti steel” hybrid material was obtained by high-pressure torsion (HPT) at different temperatures. The analysis of the structure of the hybrid material and its components was carried out by the methods of transmission and scanning electron microscopies. The distribution of chemical elements in the cross section of the hybrid material was studied by X-ray microanalysis. The microhardness was measured to estimate the hybrid material hardening after HPT. Tight joint zones between the layers of the hybrid material were formed during HPT. The fragmentation of the steel and vanadium alloy layers was observed, and the “mixing” of the layers occurred after HPT at 293 K and 473 K (20 °C and 200 °C). A smoother interface between the layers was observed after HPT at 673 K (400 °C). The significant hardening (2.0 to 3.5×) of each layer of the hybrid material was observed as a result of HPT.

Impact Property of Low-Activation Vanadium Alloy NIFS-HEAT-2 After Electron Beam Welding and Neutron Irradiation

In order to investigate the effect of post-weld heat treatment (PWHT) and post-irradiation annealing (PIA), electron-beam-weld specimens of the reference low activation vanadium alloy, NIFS-HEAT-2, were neutron-irradiated to a fluence of 7.62 × 1023 neutron m−2 (E > 1 MeV) at 563 K in Belgian Reactor-2. In the present experiments, unexpected oxidation of the surface of the samples occurred during the neutron irradiation, and significantly degraded impact properties of the weld metal, while the degradation was not significant for the base metal. The removal of the oxidized layer by electro-polishing improved the impact properties of the weld metal. Although complete removal of the oxidized layer could not be confirmed, it is revealed that impact absorbed energy of the weld metal with post-weld heat treatment at 1073 K was comparable to that of the base metal after the post-irradiation polishing. In other words, irradiation embrittlement of the weld metal was successfully suppressed by the PWHT. PIA at 773 K and above was effective to recover the irradiation hardening and irradiation embrittlement. Mechanisms of the irradiation hardening, irradiation embrittlement and its recovery were discussed.

Some problems of hydrogen in reactor structural materials: A review

The review concerns some problems of hydrogen in the main reactor structural materials used in the core of nuclear reactors. Zirconium alloys, steels, and vanadium alloys, as well as the hydrogen and helium synergetic effect exerted on the radiation resistance, are considered. The main sources resulting in the accumulation of hydrogen isotopes in reactor materials are discussed. The causes and consequences of hydride embrittlement of zirconium alloys at relatively low temperatures are analyzed. It is shown that hydrogen can induce the embrittlement of vessel steels through the weakening interatomic bond forces and a stabilization of radiation-induced defects. It is demonstrated that hydrogen in the presence of helium behaves like a gas that enhances the irradiation effect on the microstructure and properties of materials in many cases. The irradiation with simultaneous introduction of hydrogen and helium causes, in particular, a catastrophic swelling of chromium steels and vanadium alloys, whereas in the case of austenitic steel the effect is less pronounced.

Clinical outcomes of patient-specific porous titanium endoprostheses in dogs with tumors of the mandible, radius, or tibia: 12 cases (2013-2016).

OBJECTIVE To characterize the processes involved in and outcomes achieved with custom-designed patient-specific implants to provide functional replacement of skeletal structures in dogs with tumors of the mandible, radius, or tibia. DESIGN Prospective case series. ANIMALS 6 dogs with mandibular tumors, 5 with tumors of the distal aspect of the radius, and 1 with a tumor in the distal aspect of the tibia treated from June 2013 to September 2016 at 3 referral centers. PROCEDURES After tumor staging, implants were designed from patients' CT scans by means of various computer-aided design applications and printed by means of selective laser melting in titanium-6 aluminum-4 vanadium alloy. A cutting jig was created in thermoplastic to ensure each osteotomy was performed as planned. Following ostectomy, the implant was secured into the defect with screws of appropriate size and length. RESULTS Initial return to normal clinical function was good to excellent for 11 of the 12 dogs. However, major complications resulted in revision of the implant or amputation of the limb in 5 dogs, and at least 3 of these complications were considered a consequence of faulty implant design or manufacturing. Infection developed in 2 dogs and was successfully treated in 1 dog. The longest-surviving dog maintained good limb function for 2 years. CONCLUSIONS AND CLINICAL RELEVANCE This is the largest reported series of dogs managed with customized 3-D-printed titanium implants. The 3-D printing allowed complex and patient-specific 3-D geometries to be fabricated, enabling function-sparing treatment of bone cancer affecting multiple anatomic sites.

A phenomenological study of the incomplete grain evolution in a deformed vanadium alloy

The dynamic recrystallization (DRX) behavior of a V-5Cr-5Ti (wt%) alloy was studied with a view to optimizing its hot working behavior. Uniaxial compression tests were performed over the temperature range 1373 to 1673K and strain rate range 0.001 to 1.0s−1 and the microstructural changes were examined by EBSD. Discontinuous dynamic recrystallization (d-DRX) was observed to take place in addition to continuous dynamic recrystallization (c-DRX) despite the bcc nature of this alloy. The new grains nucleated at triple junctions and along grain boundaries to form a necklace structure. Some DRX grains formed within shear bands and deformation bands as well as in the matrix when the Zener-Hollomon (Z) parameter and the strain were increased. The critical stresses and strains increased with Z while the DRX grain size decreased with Z.

Influence of the pretreatment and curing of alkoxysilanes on the protection of the titanium–aluminum–vanadium alloy

ABSTRACTThe use of coatings based on alkoxysilanes is one of the most effective ways to control the release of cytotoxic ions by metal implants. To improve the success rate of titanium–aluminum–vanadium implants, in this study, we evaluated the physicochemical, morphological, mechanical, and electrochemical behavior of hybrid coatings based on alkoxysilanes applied on the alloy. The coatings were prepared with the precursors 3‐(trimethoxysilyl propyl)methacrylate and tetraethoxysilane alkoxides by the sol–gel method. The curing of the coatings was evaluated at different temperatures (90, 180, and 300 °C) for 1 h. We carried out the pretreatment of the alloy by polishing and attacking it with sodium hydroxide. The results indicate that the temperature of 90 °C was effective for solvent evaporation and complete crosslinking of the film, and the alkaline pretreatment allowed the formation of a film with better anticorrosive performance; this indicated that the presence of hydroxyl groups on the surface improved the coating adhesion. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45470.

Dissimilar-Metals Bonding Between NIFS-HEAT-2 Vanadium Alloy and Hastelloy X Nickel Alloy by Controlling Intermetallics

Dissimilar-metals joints between vanadium alloy NIFS-HEAT-2 (NH2) and nickel alloy Hastelloy X (HX) were developed by electron beam welding (EBW). If without filler, the joint fractured several minutes after the welding due to hard and brittle intermetallics formed in the weld metal (WM). Pure Ni filler with 0.2–1.0 mm in thickness decreased the content of intermetallics and eliminate hardening in the WM. However, there is always a hardening interlayer estimated as Ni2V and σ intermetallics, existed with thickness of 50 µm between NH2 base metal (BM) and WM. The hardening cannot be eliminated by annealing at high solution temperature of 1373 K. Aging at 723–973 K for 100 h further increased the hardening not only in the hardening interlayer but also in the WM. Pure Cu filler was also investigated. For the joint with 0.5 mm thick Cu filler, there are still hardening interlayer and hardening areas in the WM due to Ni2V and σ intermetallics. However, by increasing the Cu filler to 1 mm thick, the hardening interlayer disappeared by preventing mixture of NH2 and HX to form intermetallics. In this case, Charpy impact property of the joint with 1 mm thick Cu is much improved with ductile-to-brittle transition temperature (DBTT) less than 77 K. Even after thermal aging at 973 K for 100 h, the impact property did not degrade.

Fibroblast and pre-osteoblast cell adhesive behavior on titanium alloy coated with diamond film

It is well known that titanium alloys have mechanical strengths comparable to steels, as well as high corrosion resistance. Also, they have the advantage of promoting osseointegration, when used in medical and dental implants. This work aims to describe the adhesion properties of fibroblast and osteoblast cells on the surface of titanium aluminum vanadium alloy (Ti6Al4V). Three different conditions of the surface were investigated: smooth, rough and covered with diamond film. Conventional material characterizations were performed to the film which consisted in: Morphological visualization by scanning electron microscopy, confocal profilometry, X-ray diffraction pattern, Raman backscattering spectroscopy and atomic force microscopy. Biocompatibility tests of Ti6Al4V were performed using primary human fibroblasts and mouse pre-osteoblasts cell line MC3T3-E1. Overall, diamond films deposited on Ti6Al4V showed interesting results of uniformity and protection against cracks on to the surface, reasonable biocompatibility features if compared to uncovered ones, indicating that this film is an alternative for using in health care applications.

Dynamic assessment of direct-current mobility in field-assisted sintered oxide dispersion-strengthened V-4Cr-4Ti alloys

BackgroundVanadium alloy is one of the potential candidate material for structural applications in a commercial fusion reactor. Extended survival of a structural material has a direct consequence on the net energy produced in a fusion reaction, it is important to develop ultra-functional materials with tailored microstructures, to meet the harsh fusion environments. Microstructure of material, indeed depend upon the thermodynamics and kinetics of material processing.MethodsAiming to meet the harsh fusion conditions, we have developed oxide dispersion strengthened V-4Cr-4Ti alloys by high energy ball milling and field assisted sintering technique. Possible microstructural, morphological aftermaths observed in ball milled yttria dispersed V-4Cr-4Ti powders is explored.Results and conclusionElectron microscopy and laser particle analysis acknowledge that yttria addition aids powder agglomeration during ball milling. Ball milled powder was then consolidated (to a relative density of ~100%) using field assisted sintering technique, under optimal sintering conditions. Densification profile has implied that heterogeneous powder characteristic (apparent particle size and shape of powder) tends to impede the direct-current conductivity across the powder particle during various stages of field assisted sintering. In order to understand the kinetics of the field assisted sintering process on the starting powders, a new method was developed to compute the activation energy required for the direct-current conductivity across the individual powder particles. Relatively higher activation energy (for direct-current conductivity) is required for sintering yttria dispersed V-4Cr-4Ti powder than its V-4Cr-4Ti counterpart.Graphical Quantitative dynamic sintering kinetics analysis of FAST processed vanadium alloys

Structure-properties relationship of ultra-fine grained V-microalloyed dual phase steels

The effect of vanadium microalloying on ultra-high strength dual phase (DP) ferrite-martensite steel microstructure and properties was studied. It was found that the addition of 0.14wt% V to a Fe-0.18C-1.5Mn-0.3Si-0.008N reference alloy introduced very significant ferrite grain size refinement in the cold rolled and annealed state. During continuous annealing the initial ferrite to austenite transformation kinetics were strongly retarded, however under slow cooling both pearlite and bainite transformations were suppressed indicating increased hardenability. After cold rolling and intercritical annealing at 750⁰C intense V(C,N) precipitates (mean radius 3.7nm) were observed in the ferrite phase whereas precipitates were scarce in martensite (austenite) and much larger (mean radius 6.7nm). Significant gains in YS, UTS and work hardening rate were observed at low martensite fractions due to a combination of selective precipitation strengthening and grain refinement of ferrite. However, at higher martensite fractions (> 45%) the YS, UTS and work hardening rate became lower than the reference, primarily due to softening of the martensite. The latter was attributed to the fixing of solute carbon by V(C,N). The net increase in tensile strength with martensite content of the vanadium alloy was ~ 4MPa/%α’ compared to ~ 16MPa/%α’ for the reference alloy. A recently developed size-sensitive mean field structure-properties model was extended to capture these microalloying effects. At iso-tensile strength both the fracture strain and hole expansion behaviour of the new microalloyed steel showed improved performance over the reference.

Effect of the chemical composition and the structural and phases states of materials on hydrogen retention

The results of investigation of the effect of chemical composition and structural and phase states of reactor steels and vanadium alloys on their capture and retention of hydrogen introduced into the materials in various ways are presented. It is shown that, in the case of identical conditions of hydrogen introduction, the amount of hydrogen captured by austenitic steels is substantially higher than that captured by ferritic/ martensitic steels. At the same time, the EP450 ODS ferritic/martensitic steel dispersion-strengthened with nanosized yttrium oxide particles retains a substantially higher amount of hydrogen as compared to that retained in the EP450 matrix steel. The alloying of vanadium with tungsten, zirconium, and titanium leads to an increase in the amount of retained hydrogen. The effect of titanium content on hydrogen retention is found to be nonmonotonic; the phenomenon is explained from a physical view point.

Dissolution Behaviour of Alloying Elements Into Vanadium Matrix During Mechanical Milling

Mechanical alloying (MA) is an efficient approach for fabricating ODS alloys and structural materials including vanadium alloys for fusion and fission applications. Dissolution behavior of the alloying elements is a key issue for optimizing the mechanical alloying process in fabricating vanadium alloys. This paper studies the MA process of V-4wt.%Cr-4wt.%Ti alloy. The outcomes of the MA powders in a planetary ball mill are reported in terms of powder particle size, morphology and composition evolution. The impact of spark-plasma sintering process on the mechanically alloyed powder is analyzed. The microstructure of the V-4wt.%Cr-4wt.%Ti alloy prepared by mechanical milling is investigated with a X-ray diffractometer and scanning electron microscope.

Hydrogen permeability and structure of vanadium alloy membranes

Experimental data on hydrogen permeability through membrane alloys V85Ni15, V90Ti10, and V90Co10 (at %) are presented. Hydrogen permeability tests have been carried out in the temperature range of 623–873 K at pressures of ~4.5, 14, and 30 kPa. Results of X-ray diffraction analysis of samples are presented. Microstructure of the membrane alloys has been investigated before and after hydrogen permeability tests.

Influence of high-temperature ion irradiation on microstructures of the deformed and heat-treated V-4Cr-4Ti alloy

As one of candidate structural materials for future fusion reactors, vanadium alloy has been widely studied in recent decades. In the present investigation, an attempt was made to determine the influence of high energy ions irradiation on the microstructures of V-4Cr-4Ti alloy which had been subjected to aging, cold deformation and heat-treatment. To achieve the aim, aging and cold reduction were carried out, followed by isothermal heat-treatment at 1100°C for different time. Hardness measurement, optical and electron microscopies were employed to characterize microstructures of the samples. It was found that Ti-rich precipitates coherent to the matrix occur during aging. In the deformed samples, dislocation movement are inhibited by the precipitates, from which dislocation-precipitates interaction are formed. After 550keV Fe10+ irradiation at 500°C, a lot of voids, dislocation loops and fine precipitates occur in the alloy. The orientation of irradiation induced precipitates (Vanadium Carbide) is random. The sizes of voids are smaller in the annealed samples. The dislocation networks in the aged sample can remain partially after irradiation, due to pinning effect of precipitates formed during aging.

Natural convective heat transfer analysis of MHD unsteady Carreau nanofluid over a cone packed with alloy nanoparticles

The present numerical simulations are carried out to investigate the effect of viscous dissipation, temperature dependent viscosity and heat source/sink on magnetohydrodynamics (MHD) unsteady Carreaue nanofluid over a cone filled with different alloy nanoparticles. We considered two different types of alloy nanoparticle namely nickel chromium iron alloy (Nimonic 80A) and titanium aluminum vanadium alloy (Ti%6Al%4V). The governing equations of the flow are solved using the Runge-Kutta and Newton's method. The present numerical results are compared with the previous study and found agreement with the uncertainty of ±2.5%. Effects of various non-dimensional parameters such as Eckert number, power index parameter, volume fraction, heat source/sink parameter, viscous variation parameter and semi-vertical angle of the cone on the momentum and thermal boundary layer including the friction factor coefficients and local Nusselt number are presented and analyzed for two different alloy considered in the present study. It is found that the viscous variation parameter enables to enhance the heat transfer rate. The Ti%6Al%4V alloy has higher friction factor coefficient along the azimuthal direction of the flow while Nimonic 80A alloy boosts up the friction coefficient along the tangential direction. It is worth to mention that the heat transfer rate of Nimonic 80A alloy is higher than that of Ti%6Al%4V alloy. Hence, Nimonic 80A alloy signifies a better thermal performance than the Ti%6Al%4V alloy.

Molecular Dynamics Simulations of the Excess Vacancy Evolution in V and V-4Ti

Titanium additions suppress the radiation swelling in vanadium alloys, but the mechanism of the suppression is debatable. It is claimed that interactions of Ti atoms with vacancies in vanadium are crucial in the suppression. In this paper we study clustering of excess vacancies in pure V and V-4Ti by molecular dynamics simulations at 700 K based on our interatomic potentials constructed earlier for the Ti-V system. For pure V the process results in the formation of a Frank sessile dislocation while the clustering in V-4Ti ends with the formation of the Ti-vacancies complexes with a specific structure. This allows us to discuss a possible mechanism of the swelling reduction in V caused by Ti alloying.

Formation of Nanostructured State in an Internally Oxidized Vanadium Alloy Under Severe Plastic Deformation

Using the method of transmission electron microscopy, the features of structural-phase state of an internally oxidized V–Cr–Zr–W alloy following severe plastic deformation by the method of torsion on Bridgeman’s anvils are investigated. A quantitative evaluation of the parameters of grain and defect structure is performed and the characteristic dimensions and phase composition of fine disperse particles are determined. The main factors controlling the special conditions of formation of nanostructured states are analyzed.

Effect of oxygen impurity in sodium–potassium melt on the corrosion processes at the interface between vanadium alloy and eutectic melt

An analysis of available experimental data on thermodynamic activity coefficient of oxygen in binary liquid metal Na–K alloys is carried out. Thermodynamic correlations based on the coordination cluster model are used for theoretical evaluation of the effect of oxygen impurity on the solubility of vanadium in sodium–potassium eutectic alloy in the temperature range of 400–800°C. Isothermal capsule experiments qualitatively confirm the results of calculations of vanadium solubility in Na–K melt. On the basis of derived thermodynamic relationships the threshold concentration for the formation of ternary oxide NaVO2 on the surface of the solid vanadium in the Na0.32K0.68 melt has been calculated. The calculation results are compared with the corresponding values for the sodium coolant.

A high-entropy V35Ti35Fe15Cr10Zr5 alloy with excellent high-temperature strength

Low-activation structural materials for fusion applications beyond 700°C are desired. High-entropy alloys (HEAs) with excellent properties at elevated temperatures are suitable for use in nuclear reactors. A newly developed V35Ti35Fe15Cr10Zr5 HEA was fabricated by vacuum arc melting and the microstructure of as-cast and annealed sample was found to be composed of BCC solid solution phases. It was interesting to find that the yield strength of as-cast V35Ti35Fe15Cr10Zr5 HEA increased with increasing the temperature below 500°C, and it was much higher than that of vanadium alloy or martensitic steel for fusion reactors in the temperature range of room temperature to 900°C. At 700°C, the yield strength of V35Ti35Fe15Cr10Zr5 HEA was about 500MPa higher than that of vanadium alloy or martensitic steel, showing promise for high temperature applications. V35Ti35Fe15Cr10Zr5 alloy had a relative low ductility below 700°C, while the alloy exhibited a good ductility above 700°C.

The effects of interstitial impurities on the mechanical properties of vanadium alloys: A first-principles study

This study aims to elucidate the effects of interstitial impurities on the mechanical properties of vanadium alloys investigated by means of the first-principles computations. For this purpose, we study the generalized stacking-fault energies and the ductility parameters in different slip system to evaluate the strengthening and ductility potentials of interstitial impurities in V alloys. The results show that the generalized stacking-fault energy values for two slip systems all increase significantly after adding C, O, and N impurities in comparison with pure V. Moreover, the impurities located in the slip plane greatly increase the generalized stacking-fault energy, suggesting that the impurity effect is localized. The calculations reveal a remarkably strong dependence of the USF energies on the impurities concentration. Though evaluating the generalized stacking-fault energies and the ductility parameters, we draw a conclusion that impurities not only strengthen the V alloys but also reduce their plasticity.