Nb-Mo Alloys Research Articles

Novel MRI-compatible Zr–Mo–Nb alloys with superior mechanical performance, high corrosion resistance and good cytocompatibility for biomedical applications

Nowadays, MRI diagnostics have become indispensable in modern medicine, and the development of MRI-compatible materials is an urgent requirement for both modern medicine and materials science. Herein, MRI-compatible Zr–Mo–Nb alloys were developed by plasma arc melting and hot rolling process for biomedical applications. The Nb addition induces the composition segregation, β-Zr phase precipitations, and significant grain refinements in Zr–1Mo-xNb alloys, thereby contributing to an ultrafine α+β lamellar structure in hot-rolled (HRed) Zr–1Mo–3Nb alloys. Thanks to the nano-sized α+β lamellar structure, a high yield strength (YS) of 819.6 ± 20.9 MPa and an acceptable elongation of 11.8 ± 1% were realized in the HRed Zr–1Mo–3Nb alloy. Additionally, the incorporation of Nb with a high PB ratio and a relatively high equilibrium potential in the Zr–1Mo matrix enhances the stability of the passivation layer, leading to a more positive corrosion potential. Consequently, this significantly improves the corrosion resistance of HRed Zr–1Mo-xNb alloys. The Zr–1Mo–3Nb alloy exhibits lower magnetic susceptibility than the Zr–1Mo alloy, indicating improved MRI compatibility. Moreover, the HRed Zr–1Mo-xNb alloy shows excellent cytocompatibility to MC3T3-E1 cells, and good hemocompatibility of the experimental alloys were confirmed by the blood compatibility test. These findings highlight the potential of the MRI-compatible Zr–1Mo–3Nb alloy as a promising material for implants and devices in MRI environments, offering superior mechanical performance, high corrosion resistance and good biocompatibility.

Atomic mobilities, diffusion coefficients, and kinetic coefficients in Ti-rich Ti–Mo–Nb system

Diffusion coefficient is an important physical property to control the microstructure, thus the establishment of atomic mobility databank for Ti-based alloy systems is vital to the design of novel Ti alloys. In the present work, ternary Ti–Mo–Nb diffusion couples within the single bcc phase were prepared and measured after annealing at 1273 K for 25 h, and interdiffusion coefficients of bcc Ti–Mo–Nb alloys at 1273 K were determined from the experimental composition profiles by using Matano–Kirkaldy method. Subsequently, the atomic mobility parameters of bcc Ti–Mo–Nb system under the CALculation of PHAse Diagrams (CALPHAD) framework were assessed by using recently proposed diffusion models, which were verified by the comparisons between the experimental interdiffusion coefficients/composition profiles and the model-predicted results. Moreover, diffusion models were carefully discussed for the ternary assessment. Finally, relationships among atomic mobility, kinetic coefficient, and diffusion coefficients were discussed and demonstrated via ternary contour maps. The present work contributes to the development of diffusion databank for computational design of biomedical Ti alloys.

Modifying Microstructure and Mechanical Properties of Mo-Nb Single Crystals via Thermal Annealing

Molybdenum-Niobium (Mo-Nb) single crystals possess excellent mechanical properties, such as high strength and low creep rate at high temperatures, which leads to Mo-Nb single crystals’ potential application in the irradiated and aerospace environment. Mechanical properties at high temperatures are closely related to structural defects, including the density of dislocation and low-angle grain boundaries in a single-crystal Mo alloy. It is well known that the density of defects is mainly contributed to by processing and annealing. To clarify the microstructural evolution of Mo-Nb single-crystal alloys, thermal annealing tests with temperatures varying from 1100 °C to 1700 °C were conducted. Two Nb contents (3 at.% and 6 at.%) were chosen to investigate the effect of Nb content on the thermal stability (≤1700 °C) of single-crystal Mo-Nb alloys. Samples with high Nb content (6 at.%) soften after annealing, while ductility at room temperature obviously enhances In the low Nb content (3 at.%) sample, however, hardening and softening occur after low (1100 °C) and high temperature annealing, respectively. The evolution of mechanical properties could be mainly attributed to the change of density in the low-angle grain boundary. Furthermore, the changing Nb element and dislocation density during annealing are still important to the strength and ductility of Mo-Nb single crystals.

Mechanical properties of (HfCo)100−x(NbMo)x refractory high-entropy alloys with a dual-phase bcc-B2 structure

The common concept for the development of the high-performance metallic materials is associated with the combination of a soft disordered matrix and hard ordered reinforcements. However, unusual combinations of a hard disordered phase and a soft(er) ordered phase are also possible. In this work, we explored structure and mechanical properties of (HfCo)100−x(NbMo)x (x = 0; 10; 25; 60; 75; 100 at%) refractory high-entropy alloys. The binary HfCo and NbMo alloys had ordered B2 and disordered bcc structures, respectively. The (HfCo)100−x(NbMo)x (10 ≤ x ≤ 75) alloys had mostly a dual-phase structure of disordered (Nb, Mo)-rich bcc and ordered (Hf, Co)-rich B2 phase. Almost fully a eutectic-like structure was found in the (HfCo)75(NbMo)25 alloy. "Cube-on-cube" orientation relationships between the bcc and B2 phases ((110)bcc||(110)B2, [001]bcc||[001]B2) were detected. In addition, a small amount of Nb-rich bcc and/or Hf-rich fcc oxide phases were detected in some alloys. The B2 HfСo alloy was ductile but extremely soft, while, the NbMo alloy was hard and brittle. Simultaneous improvement of strength and ductility in the dual-phase (HfCo)100−x(NbMo)x (10 ≤ x ≤ 75) was revealed. The (HfCo)90(NbMo)10 alloy with a close to single-phase B2 structure exhibited a yield stress anomaly (YSA) at 500 °C. The YSA was associated with a change of dominant slip mode from a<100>to a<110>. Relationships between the chemical composition, microstructure, and the mechanical properties of the (HfCo)100−x(NbMo)x alloys were discussed.

The absolute thermoelectric power of Nb–Mo alloys

Abstract After Onsager the thermopower of a material is related to the ratio either of two transport coefficients or of the gradients of the electrochemical potential of the electrons and the temperature. In metals the potential is a unique function of the temperature and this ratio can be replaced by the differential quotient, a function obtainable from the density of states of the metal as illustrated on a thermopower isotherm of Nb–Mo alloys.

Microstructure, mechanical and wear properties of mechanically alloyed and conventionally sintered Nb-W and Nb-Mo alloys

Nb-W and Nb-Mo exhibit unrestrained solubility in liquid and solid phase, leading to influence the mechanical properties of Nb. In the present work 90Nb-10 W (alloy A) and 90Nb-10Mo (alloy B) (in weight%) are synthesized by mechanical alloying for 10 h and consolidated by conventional pressureless sintering in argon atmosphere at 1450 °C with 2 h of soaking time. The effect of compaction pressure (375 MPa, 500 MPa, 625 MPa) on densification before sintering and densification, hardness after sintering of the alloys is also investigated. Plastic-assisted deformation is more in alloy B against alloy A which enhances the densification during sintering. Elemental mapping and line scanning result of sintered alloy A show the incidence of W in Nb phase, suggesting profound inter-diffusion of W/Nb. Maximum % relative sintered density of 68.89% is achieved in alloy B at 500 MPa pressure. Alloy A exhibits maximum hardness of 3.11 GPa at 625 MPa compared to 2.55 GPa hardness for alloy B compacted at identical compaction pressure. The wear resistance of alloy B is comparatively higher than alloy A, both compacted at 500 MPa pressure.

Room and high temperature mechanical behavior of Ti–Al–Nb–Mo alloy reinforced with Ti2AlN ceramic particles

In order to improve the room and high temperature mechanical properties of Ti46Al4Nb1Mo alloy, Ti46Al4Nb1Mo-xN (x = 0, 0.4%, 0.8%, 1.2%, 1.6%, atomic percent, hereafter in at.%) alloys were prepared by adding TiN powders. Results showed that when the N addition was more than 0.8%, the grain morphology changed from columnar dendrites to equiaxed grains due to the formation of Ti2AlN particles, and the equiaxed grain size decreased with further increasing of the N addition. With 1.6% N addition, the compressive strength increased by 16.8% at room temperature, which was due to the collective strengthening effect of lamellae refinement and Ti2AlN particles. While lamellae refinement and Ti2AlN particles had opposite effects and competed with each other at high temperature, strengthening by Ti2AlN particles had the dominant effect on improving the peak stress of the Ti46Al4Nb1Mo-1.6 N alloy, which increased by 21.8% and 24.1% at 900 °C and 1000 °C, respectively. In addition, compared with the fracture microstructure at room temperature, the deformed microstructure showed that the load transfer effect of Ti2AlN particles was more effective at high temperature, which was due to micro-damages in the Ti2AlN particles and the absence of cracks along irregular Ti2AlN particles.

Microstructures and Oxidation Behavior According to Nb:Mo Ratio in a Nb–Mo–Si System with Si Pack Cementation Coatings

Research is being conducted on Mo- and Nb-based alloys that are used in the aerospace sector, including those used for advanced gas turbines and aircraft engines. There is a limit to using Mo, which has a high density among refractory metals, and a few studies exist describing the addition of Nb to Mo–silicide alloys. There is a lack of guidance research on the basic Nb:Mo ratio of alloys, and it is necessary to study how to improve oxidation resistance. Therefore, this study aims to improve oxidation resistance by controlling the ratio of Nb and Mo in (Nbx, Moy)Si2 coating layers with Si pack cementation coatings on Nb–Mo alloys. Static oxidation tests were carried out at 1200 °C for 6 h to confirm the oxidation characteristics. As a result, a SiO2 or SiO2 + Nb2O5 ceramic protective layer was formed on the surface. After the oxidation tests, alloys with a Nb content of less than 35 at.% were found to protect the surface. The ratios of Nb and Mo in the Nb–Mo alloy and silicide coating layer were compared, and the improvement of oxidation resistance is discussed in terms of microstructural evolution.

Microstructural and mechanical properties of β-type Ti–Mo–Nb biomedical alloys with low elastic modulus

The microstructural and mechanical properties of β-type Ti74-xMoxNb26 (x = 0, 2, 4, 6, and 8 at.%) biomedical alloys with low elastic modulus were investigated. The experimental results show that the Ti74Nb26 alloy is composed of the β and α’’ phases; however, the Ti74-xMoxNb26 (x = 2, 4, 6, and 8 at.%) alloys are composed of only a single β phase. Based on the stress–strain curve, the Ti66Mo8Nb26 alloy with the large yield strength and elastic energy can consider as biomedical and functional materials. The Mo addition not only stabilizes the β phase of the alloys, but also increases the strength, and retains the ductility of the Ti74Nb26 alloy. Based on nanoindentation technique, the reduced elastic modulus (Er) of Ti66Mo8Nb26 alloy with the high hardness (H) is 54.5 GPa, which is 1.5–5.5 times of that of human bone (10–30 GPa), and is the smaller than that of commercial Ti–6Al–4V biomedical alloy (120 GPa). The wear resistance (H/Er) and anti-wear capability (H3/Er2) ratios of Ti66Mo8Nb26 alloy are 0.0591 and 0.0112 GPa, respectively, indicating that the good wear resistance and anti-wear capability, or long service life as biomedical materials, compared with those of CP-Ti alloy. In addition, the elastic recovery values of the Ti–Mo–Nb alloys are larger than that of CP-Ti alloy (20.4%), which indicates that the Ti–Mo–Nb alloys exhibit the higher impact resistance.

Influence of Ta/Zr minor-alloying on the high-temperature microstructural stability of cladding Fe–Cr–Al ferritic stainless steels

The Fe–Cr–Al-based ferritic stainless steels have attracted more attention as accident-tolerant-fuel cladding materials of nuclear reactors due to their prominent comprehensive properties. The present work investigated systematically the influence of Ta and Zr minor-additions on the microstructural stabilities at high temperatures (HTs) of Fe–Cr–Al–Mo–Nb alloys. Alloy compositions were designed in light of a cluster formula approach. Alloy ingots, in turn, were homogenized at 1473 K for 2 h, hot-rolled at 1073 K, aged at 1073 K for 24 h, and then retreated at different temperatures (1273–1473 K) for 1 h. The microstructures at different heat-treatment states were characterized with optical microscopy (OM), scanning electron microanalysis (SEM), electron probe microanalysis (EPMA) and transmission electron microscopy (TEM), respectively. The experimental results indicated that fine second-phase precipitates (primarily Laves phase) are distributed homogeneously in the ferritic matrix of aged alloys. These precipitates would be re-dissolved into the matrix when these aged alloys were retreated at a HT above 1273 K. Most of the Laves precipitates are dissolved into the matrix in the Mo/Nb/Ta-containing alloys after retreatment at 1,473 K for 1 h, while the further addition of minor Zr (about 0.1 wt %) can retard this dissolution effectively, resulting in a desirable microstructure with second-phase precipitates uniformly distributed into the refined matrix grains at HTs. Moreover, it was also found that the Zr addition can contribute to the formation of core-shell particles, in which the inner-core is enriched by Zr to form a cubic Zr2Fe phase and the out-shell exhibits a Laves phase structure segregated by Ta and Nb.

Strength design of Zr(x)Ti(x)Hf(x)Nb(x)Mo(x) alloys based on empirical electron theory of solids and molecules

In this paper, the valence electron structure parameters of Zr(x)Ti(x)Hf(x)Nb(x)Mo(x) alloys were calculated based on the empirical electron theory of solids and molecules (EET), and their performance through these parameters were predicted. Subsequently, the alloys with special valence electron structure parameters were prepared byarc melting. The hardness and high-temperature mechanical properties were analyzed to verify the prediction. Research shows that the influence of shared electron number nA on the strongest bond determines the strength of these alloys and the experiments are consistent with the theoretical prediction.

In situtransmission electron microscopy study of the thermally induced formation of δ′-ZrO in pure Zr and Zr-based alloy

This study reportsin situobservations of the formation of the δ′-ZrO phase, occurring during the annealing of transmission electron microscopy (TEM) thin foils of both pure Zr and a Zr–Sn–Nb–Mo alloy at 973 K in a transmission electron microsope. The lattice parameters of δ′-ZrO were measured and determined to be similar to those of the ω-Zr phase. The orientation relationship between the δ′-ZrO and α-Zr phases has been identified as either {(11 \overline{2}0)}_{\rm ZrO}//{(0002)}_{\alpha} and {[0002]}_{\rm ZrO}//{[11 \overline{2}0]}_{\alpha} or {(\overline{1}011)}_{\rm ZrO}//{(0002)}_{\alpha} and {[01{\overline 1}1]_{{\rm{ZrO}}}}//{[11{\overline 2}0]_\alpha} depending on the orientation of the α grain relative to the TEM thin-foil normal. The nucleation and growth of δ′-ZrO were dynamically observed. This study suggests a new and convenient way to study oxidation mechanisms in Zr alloys and provides a deeper understanding of the properties of the newly reported δ′-ZrO. Since δ′-ZrO has a Zr sublattice which is identical to that of ω-Zr, the orientation relationships between the α and δ′-ZrO phases may also shed light on the orientation relations existing between α- and ω-Zr, and hence α- and ω-Ti.

Interatomic potential to predict the glass-forming ability of Ni–Nb–Mo ternary alloys

With the recently proposed formulation, an interatomic n-body potential was first constructed for the Ni–Nb–Mo metal system, and then applied to atomistic simulations to investigate the glass formation of the Ni–Nb–Mo ternary alloys. The simulations not only clarify the atomistic process of the metallic glass formation but also predict for the ternary system of a quantitative composition region within which metallic glass formation is energetically favored. In addition, the energy difference between crystalline solid solution and disordered phase i.e., the driving force for a supersaturated solid solution to amorphize could be considered as an indicator of the glass-forming ability (GFA) for a specific alloy. The GFAs of a series of Ni–Nb–Mo alloys were derived from the simulations, leading to pinpoint the Ni55Nb30Mo15 alloy with superior GFA in this ternary metal system. The Ni55Nb30Mo15 alloy can be considered as the optimized ternary metallic glass for thermal stability and manufacturability.

Corrosion resistance of aged Ti–Mo–Nb alloys for biomedical applications

Metastable β-Ti alloys combine low elastic modulus, excellent mechanical strength as well as good corrosion resistance. Wherever, the presence of nontoxic elements such as Nb, Ta, Mo, and Zr is an important advantage. With such properties this type alloy has been developed for orthopedic applications. Previous studies had shown that the Ti–12Mo–13Nb and Ti–10Mo–20Nb alloys aged at 500°C presented higher hardness/elastic modulus ratio compared to commercially Ti–6Al–4V, indicating a great potential for biomedical application. However, additional studies are needed such as corrosion resistance. Therefore, the objective of this work was to analyze the electrochemical behavior of the Ti–12Mo–13Nb and Ti–10Mo–20Nb alloys aged at 500°C/24h and 500°C/4h, respectively. The electrochemical behavior was carried through by potentiodynamic polarization curves in Ringer’s solutions to simulate the body fluid. The Ti–10Mo–20Nb alloy showed to be more resistant to corrosion when compared to Ti–12Mo–13Nb alloy and the commercially Ti–6Al–4V alloy.

Evolution of the ωo phase in a β-stabilized multi-phase TiAl alloy and its effect on hardness

The intermetallic β-stabilized Ti–43.5Al–4Nb–1Mo–0.1B alloy (in at.%), termed TNM alloy, is designed to be used at elevated temperatures, typically up to 750°C. To understand the evolution of the microstructures during heat treatments and subsequent creep tests, an understanding of the phase transformations and decomposition reactions that occur is necessary. The present study deals with the development and growth mechanism of the ωo phase, which forms in the βo phase during static annealing treatments and creep tests performed at 750, 780 and 800°C using an applied stress of 150MPa. In situ high-energy X-ray diffraction experiments were conducted to investigate the decomposition behaviour of the ωo phase during heating as well as to determine its dissolution temperature. High-resolution transmission electron microscopy was used to study the coarsening of ωo grains during creep. The chemical composition of βo and ωo was determined by means of energy dispersive X-ray microanalysis. In particular, the impact of the Mo content on the growth of the ωo grains within the βo matrix was investigated. Additionally, nanohardness measurements in γ, α2, βo and (βo+ωo) grains were performed by cube corner indentation. The results show that βo is the hardest phase in the TiAl–Nb–Mo alloy system when finely dispersed ωo precipitates are present.

High temperature oxidation behaviour of TiAl–Cr–Nb–Mo alloys

The oxidation behaviour of six different TiAl–Cr–Nb–Mo alloys was investigated by thermogravimetric method. Isothermal experiments were carried out at 900 °C and 1000 °C in air.The aim of this work was to evaluate the effect of aluminium and of other alloying elements on the oxidation behaviour of TiAl intermetallic alloys. The alloy's microstructure and composition as well as the composition distribution of the oxide scales were analysed by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-Ray Diffractometry (XRD). The study highlighted that the oxidation resistance of the considered TiAl-based alloys is strongly affected by its aluminium content, while it seems that an increase of Cr, Nb and Mo concentrations does not affect the oxidation behaviour of the alloy. Yttrium addition, at least in the tested quantity, has a detrimental effect since it promotes the formation of a TiO2–Al2O3 mixed oxide instead of a compact and thin alumina layer.

Absorption and desorption of H by NbMo alloys at high temperature

Absorption and desorption of hydrogen have been investigated in Nb95Mo5 and Nb80Mo20 alloys over wide temperature ranges. On continuous heating H desorption from Nb95Mo5 was found to take place between 800 and 1000 K and from Nb80Mo20 between 900 and 1100 K. The observed increase in the desorption temperature with increasing Mo content has been attributed to a higher stability of the Mo and NbMo oxides with respect to those of Nb. The solid–gas reaction during absorption was first order and the rate limiting process consisted in the penetration of H atoms through surface oxides. At high temperatures and in the presence of H the oxides are expected to become permeable to H due to the reduction of higher valence to lower valence oxides. The values of the activation energy for H diffusion within the oxide films were 0.82 ± 0.04 eV for Nb95Mo5 and 1.1 ± 0.1 eV for Nb80Mo20. The thicknesses of the oxide films estimated from the absorption data were of the order of 1 μm.

First-principles calculations of elastic moduli of Ti–Mo–Nb alloys using a cluster-plus-glue-atom model for stable solid solutions

Using the first-principles calculations, a cluster-plus-glue-atom model was employed to investigate the elastic and electronic properties of Ti–Mo–Nb alloys with cluster formula of [MoTi14] (glue atom)x (glue atom = Ti, Mo, Nb, x = 1 or 3) for a theoretical guidance in composition design of β titanium alloys. The bulk modulus, shear modulus, Young’s modulus, and Poisson ratio were evaluated from the calculated elastic constants using Voigt–Reuss–Hill average scheme on the periodic supercell model of cluster packing. The electronic properties of the Ti–Mo–Nb alloys were discussed by analyzing the electron density of state and Mulliken population. Meanwhile, we designed two series of Ti–Mo–Nb alloys, i.e., [MoTi14]X1 (X = Ti, Mo, Nb) and [YTi14]Nb3 (Y = Ti, Mo), and experimentally measured their mechanical properties. Our theoretical results (including mass density, Young’s modulus, ductility) based on our cluster packing model agreed well with the experimental data, especially for [TiMo14]X1 (X = Ti, Mo, Nb) alloy series. On the contrary, the random solid solution structures were mechanically unstable and the calculated values significantly deviated from the experiments. Based on the cluster-plus-glue-atom model, an Ashby map of E/ρ versus B/G was constructed and indicated the inverse correlation between stiffness and ductility, for which the random solid solution model was unable to reflect. The Mo/Ti = 1/14 rule derived from the cluster model may serve as an important guideline for composition design of Ti–Mo based systems to achieve low elastic modulus alloys with stable β phase.

Retraction of “Composition design and mechanical properties of BCC Ti solid solution alloys with low Young’s modulus”

(Ti-Zr)-Mo-Nb alloys were studied to find some stabilized BCC solid solution with low Young’s Modulus. We propose a cluster-plusglue-atom model to solve the composition design of multi-component complex alloys from the structure viewpoint. The alloy composition is expressed with [cluster](glue atom)x according to the model, x denoting the number of glue atoms matching one cluster. Alloy structures were identified with XRD and optical microscopy (OM), and mechanical tests were finally carried on to the BCC alloys. The experimental results indicated that a series of β-Ti solid solution alloys with low Young’s modulus and good synthesized mechanical properties can be obtained with the cluster model, where the [CN14 cluster](glue)1 alloys given by of 1:1 cluster model have the optimum properties.

Long- and short-range motions of H and D in a NbMo alloy as studied by anelastic relaxations

The diffusion of H and D has been investigated in the Nb0.80Mo0.20 alloy by Gorsky and dipole reorientation/reaction relaxations in the temperature ranges 130–370 K and 70–100 K, respectively. Between 130 and 370 K the chemical diffusion coefficient at infinite dilution of H and D obeys Arrhenius laws. Differently from the case of pure Nb no deviation from an exponential temperature dependence has been observed below 250 K. The activation energies in the alloy (0.113 ± 0.003 eV for H and 0.13 ± 0.02 eV for D) are slightly higher than in pure Nb (0.106 ± 0.006 eV for H and 0.127 ± 0.006 for D) for T > 250 K. The H diffusion data were fitted to a relationship provided by a trapping model and the binding energy of H to Mo was found to be as small as 0.009 eV. An internal friction (IF) peak occurring between about 70 and 100 K for frequencies in the range 0.50–6.62 kHz was proved to be due to stress-assisted changes in the directional short-range order of Mo–H(D) bonds. The Einstein diffusion coefficient of H(D) deduced from the IF peak does not match the higher temperature data due to differences in the tunneling regimes of free and trapped H atoms operating over the two temperature ranges. The mismatch is small for D for which the tunneling regime appears to be the same in the free and trapped states.