Nb Hf Research Articles

Effect of C additives with 0.5 % in weight on structural, optical and superconducting properties of Ta–Nb–Hf–Zr–Ti high entropy alloy films

We investigated the superconducting (SC) properties of Ta–Nb–Hf–Zr–Ti high-entropy alloy (HEA) thin films with 0.5 % weight C additives. The C additives stabilize the structural properties and enhance the SC critical properties, including μ0Hc2 (13.45 T) and Tc (7.5 K). The reflectance of the C-added HEA film is enhanced in the low-energy region, resulting in a higher optical conductivity, which is consistent with the lower electrical resistivity. In addition, we observed SC vortices in the C-added HEA film using magnetic force microscopy. The magnetic penetration depths (λ) of the pure HEA and C-added HEA films were estimated from their Meissner force curves by comparing them with those of a reference Nb film. At 4.2 K, the λ of the C-added film is 360 nm, shorter than that of the pure HEA film (560 nm), indicating stronger superconductivity against an applied magnetic field.

Microstructure and Thermoelastic Martensitic Transformation in Ni-Low and -Rich Ni–Ti–Hf–Nb Hightemperature Shape Memory Alloys

Microstructure and Thermoelastic Martensitic Transformation in Ni-Low and -Rich Ni–Ti–Hf–Nb Hightemperature Shape Memory Alloys

Superconductivity with a high upper critical field in an equiatomic high-entropy alloy Sc–V–Ti–Hf–Nb

High-entropy alloy (HEA) superconductors have attracted significant attention due to their exceptional low-temperature mechanical and superconducting properties. We report the synthesis and thorough characterization of an equiatomic HEA superconductor with the composition Sc0.20V0.20Ti0.20Hf0.20Nb0.20, crystallizing in a body-centered cubic crystal structure (Im3m¯). Our investigation, using magnetization, transport, and heat capacity measurements, reveals the presence of weakly coupled, fully gapped superconductivity with a transition temperature of 4.17(3) K and the upper critical field exceeding the Pauli paramagnetic limit. The metallic nature, combined with a high upper critical field, positions it as a promising candidate for applications in superconducting devices.

Convergent plate boundary environments for formation of ≥ 3800 Ma mafic–ultramafic assemblages (Isua area, Greenland): Implications for early global geodynamics

In the gneiss terrane on the south side of the Eoarchean Isua supracrustal belt, ultramafic rocks with relict abyssal peridotite mineralogy (Bennett et al., 2002; Friend et al., 2002; Nutman et al., 2007; Rollinson, 2007; van de Löcht et al., 2020), layered gabbros with cumulate ultramafic rocks, basalts and associated siliceous sedimentary rocks were tectonically-imbricated, prior to and during intrusion of ca. 3800 Ma tonalites. Together with ≥ 3800 Ma basalts in the Outer Arc Group of the nearby Isua supracrustal belt, the composition of all these mafic rocks (e.g., Th–Hf–Nb systematics, high Th/Yb, Ba/Nb, Ba/Yb ratios and negative Nb and Ti anomalies) shows affinity with modern suprasubduction rocks whose genesis involved fluid fluxing of the upper mantle. However, the majority of these samples have Ba/Nb and Ba/Yb values less than in modern island arc magmas, but similar to many backarc basin magmas (e.g., Pearce and Stern, 2006). It is unknown whether these ca. 3800 Ma mafic rocks are, (i) arc rocks where the Ba/Nb and Ba/Yb signatures reflect lower surficial Ba in Eoarchean oceanic settings, or (ii) in direct comparison with Phanerozoic suites, these signatures reflect a back-arc setting with interplay between fluid fluxing and decompressional melting. The tectonic intercalation of upper mantle with lower and upper crustal rocks, combined with the fluid-fluxing influences seen in chemistry of all the mafic rocks is best accommodated in a compressional Eoarchean convergent plate boundary setting within a mobile-lid regime. Thus stagnant lid scenarios of crust formation, if operative, must have co-existed or alternated with mobile-lid regimes by 3800 Ma.

Tailoring the non-coherent interfacial precipitation to overcome the trade-off between strength-ductility and impact energy release in Ti–Zr–Hf–Nb–Ta high entropy alloy

The energetic high-entropy alloys have brought a new idea for the development of new energetic structural materials (ESMs) with high energy density and excellent mechanical properties. However, the energetic high-entropy alloys exhibit a significant trade-off between strength-ductility and impact energy release efficiency. Here, we develop a new strategy to introduce non-coherent interfacial nanoprecipitates into the Ti–Zr-Hf-Nb-Ta BCC energetic high-entropy alloy, which can not only exert the precipitation strengthening mechanism to maintain excellent mechanical properties, but also transform the local shear fracture into multiple cracks along the grain boundary to promote energy release. The nanoprecipitation-strengthened energetic high-entropy alloy achieved a four-times greater fireball area generated by impact energy release than that of the single-phase BCC alloy, while maintaining an excellent mechanical property combination of high dynamic compression strength (1787 MPa) and high fracture strain (40 %). The results provide new insights into the development of energetic high-entropy alloys with superior impact energy release and strength-ductility synergy.

Thermal-driven gigantic enhancement in critical current density of high-entropy alloy superconductors

The high-entropy alloy (HEA) superconductor, Ta1/6Nb2/6Hf1/6Zr1/6Ti1/6 (Ta–Nb–Hf–Zr–Ti), is systematically studied to examine changes in superconducting critical properties, critical temperature (Tc), critical current density (Jc), and upper critical field (Hc2), concerning thermal treatment conditions. Annealing condition affects Jc more significantly than Tc and Hc2, with a large improvement of flux pinning force density (Fp). The Jc of bare sample is reduced to 10 A cm–2 at an applied magnetic field of approximately 1.5 T, whereas the sample annealed at 550 °C for 12 h exhibits Jc > 100 kA cm–2 up to around 4 T. Furthermore, the Vickers hardness (HVIT) of the Ta–Nb–Hf–Zr–Ti HEA superconductor notably increases from ∼384 to 528 HVIT following a 24-h annealing at 500 °C. These results demonstrate that thermal annealing is a powerful process to optimize both the superconducting and mechanical properties of high-entropy alloy superconductors.

Advances in Diffusion Barrier Coatings for High-Temperature Applications

Diffusion barrier coating (DBC) systems on heat resistant alloys consist of a multi-layer structure: an outer Al-reservoir layer and an inner diffusion barrier layer (DBL). The outer Al-reservoir layer forms a protective Al2O3 scale and DBL acts as a barrier layer against alloy interdiffusion. Three kinds of DBL were developed: Re on Ni-based superalloys; W on stainless steels; and Cr on Ni–Cr alloys. It was found that DBC systems have excellent mechanical properties (creep and fatigue), improving alloy substrate performance, and enhance the anti-exfoliation properties of YSZ in thermal barrier coatings (TBC) in addition to providing excellent oxidation resistance. At temperatures higher than 1300 °C, however, the DBC design based on kinetics (diffusion) is insufficient to form and maintain a protective Al2O3 scale. In this case a self-maintaining coating (SMC) system designed on the basis of thermodynamics (phase stability) is required. The SMC system formed on Nb–Hf (C-103) alloy consists of a multi-layer structure: an outer Re (Al, Si)1.8 and inner NbSi2 layers, plus a transient Nb5Si3 layers formed during oxidation. At temperatures higher than 1300 °C the Al2O3 can be formed by changing the Al/Si ratio in the Re (Al, Si)1.8 in which Si was supplied from the decomposition reaction of NbSi2 to Si + Nb5Si3 during selective oxidation of Al. It is proposed that coating alloys should be designed for considering not only high temperature oxidation, but also alloy substrate mechanical properties and anti-exfoliation of oxide scales, based on both kinetic principles (DBC system) and thermodynamics (SMC system).

An ab-initio study of induced half metallic ferromagnetism in Hf–Nb alloy oxides

An ab-initio study of induced half metallic ferromagnetism in Hf–Nb alloy oxides

Experimental investigation of phase equilibrium in the Al–Nb–Hf ternary system at 600 °C and 400 °C

The phase equilibria in the Al–Nb–Hf ternary system at 600 °C and 400 °C were experimentally investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and electron probe microanalysis (EPMA/WDS). In each isothermal sections, 13 three-phase regions were measured. And their phase region boundaries were precisely determined. Among the actually measured binary compounds, only Al3Nb, AlNb2 and AlNb3 have a large range of solid solubility. In addition, two stable ternary compounds τ1-Al11Nb4Hf5 and τ2-Al2NbHf2, which had certain solid solubility, were newly discovered. On the basis of the experimental results and reasonable inference, the isothermal sections of ternary system at 600 °C and 400 °C were constructed.

Chemical short range order and deformation mechanism of a refractory high entropy alloy HfNbTaZr under nanoindentation: An atomistic study

Refractory high entropy alloys (RHEA) are promising potential used as structural materials owing to the remarkable mechanical properties, such as excellent thermal stability and strength. However, the dynamic nanoindentation response of the nanocrystalline RHEA at atomic scale is not fully revealed. Here, the mechanical behaviour of the as-cast and annealed nanocrystalline HfNbTaZr RHEA under nanoindentation is investigated for first time using a large scale molecular dynamics simulation, in the terms of indentation force, microstructural evolution, stress distribution, shear strain distribution, and surface topography. The results show the annealed nanocrystalline HfNbTaZr RHEA has obvious chemical short-range ordered structure (CSRO), including Ta enrichment and Hf–Nb segregation. The elastic modulus of the annealed RHEA is larger than that of random RHEA, agreeing with the previous experiment. CSRO improves the indentation force and work hardening, due to the inhibition of dislocation nucleation and motion. Interestingly, the hardening behavior is found in the unloading stage, which is rarely reported in traditional alloys. The crystal-to-amorphous phase transition takes place under the loading, and the inverse phase transformation occurs under the unloading. The increase rate of high Von Mises stress and hydrostatic stress region is lower than the change rate of the high strain region. Certainly, almost all atoms move to consume stored energy after unloading, leading to the decrease of stress and strain. The current study not only gives an insight into probing the mechanical behavior of the nanocrystalline RHEA, but also provides an avenue to design high performance RHEAs based on the heat treatment process.

Interdiffusion behaviors and mechanical properties of Hf-X (X=Nb, Ta) binary systems

The diffusion behaviours and mechanical properties of the Hf-X (X = Nb, Ta) systems have been investigated using diffusion couples in the temperature range from 1150 °C to 1500 °C. The interdiffusion coefficients of Hf-X (X = Nb, Ta) systems were extracted using forward simulation analysis (FSA) based on the Sauer-Freise method. According to the results, the interdiffusion coefficients of the Hf-X (X = Nb, Ta) systems decreased as the Nb or Ta content increased. In the meantime, the diffusion activation energies of Hf-X (X = Nb, Ta) systems increased as the Nb or Ta content increased. Finally, the hardness and Young’s moduli of the Hf–Nb and Hf–Ta systems were determined by nanoindentation tests. The largest hardness values of the Hf–Nb and Hf–Ta were 5.2 GPa and 5.3 GPa, respectively. Young’s largest moduli of the Hf–Nb and Hf–Ta were 221 GPa and 238 GPa, respectively. The present results provide helpful diffusional data and mechanical properties for the materials design, research and development of hafnium-based alloys.

Interdiffusion in refractory metal systems with a BCC lattice: titanium–tantalum and titanium–multicomponent (high-entropy) alloy

In this work, the interdiffusion features in multicomponent (high-entropy) alloys of refractory metals were studied. The following pairs were chosen as the diffusion study objects: titanium–equiatomic alloy (Hf–Nb–Ta–Ti–Zr–Mo) and titanium–tantalum for the sake of comparison. The article covers the issues of sample preparation, microstructure study, sample preparation methodology for diffusion research, and experimental results. Diffusion annealing was carried out for 12 h in a vacuum at a residual argon pressure of 6.65·10–3 Pa and a temperature of 1200 °С. Particular attention was paid to the method of combining diffusion pairs (titanium with tantalum, titanium with alloy) by thermal cycling near the polymorphic transformation temperature in titanium (882 °C) within ± 50 °C. The behaviour of the most characteristic elements (Ta, Zr, Ti) in the weld area after the titanium and alloy diffusion pair joining was demonstrated. This is the first time that data on the dependence of the intensity of the corresponding spectral line for titanium and elements of a multicomponent alloy on the penetration depth were obtained. A change in the signal intensity for system elements was observed at a depth of 150–200 μm, whereas a sharp drop in the signal intensity was seen to occur at depths of about 50 μm. The effective value of the coefficient of diffusion of elements into titanium averaged over all elements of the alloying system (except for titanium) at a temperature of 1200 °C was calculated. The obtained value was compared to reference data: the self-diffusion coefficient in β-titanium and diffusion coefficients in titanium pairs with alloy doping elements.

Experimental investigation and thermodynamic description of the Fe–Hf–Nb system

According to solidification microstructure of as-cast alloys and phase constituents of annealed samples, the liquidus surface projection and phase relationships at 1373 and 1273 K in the Fe–Hf–Nb system were constructed. A ternary phase τ with AlCuHf-structure was found, and the composition ranges of Nb in τ at 1373 and 1273 K were ∼ 20.5–30.8 at.% and ∼ 20.8–30.2 at.%, respectively. Moreover, the maximum solubilities of Nb in FeHf2 was determined to be ∼ 16.9 at.% and ∼ 16.0 at.% at 1373 and 1273 K, and the maximum solubilities of Hf in μ was measured to be ∼ 4.6 at% and ∼ 3.3 at.% at 1373 and 1273 K. Fe2Hf and Fe2Nb with the same C14 structure formed a homogeneous solid solution from Fe2Hf to Fe2Nb at 1373 and 1273 K. Seven primary solidification regions in the liquidus surface projection and two three-phase regions and seven two-phase regions in the isothermal sections at 1373 and 1273 K were experimentally determined. On the basis of experimental data, the thermodynamic parameters of individual phases in the Fe–Hf–Nb system were optimized by CALculation of PHAse Diagram (CALPHAD) method. Four solution phases (liquid, bcc, fcc, and hcp) were described as the substitutional solution. The intermetallic phases FeHf2, λ1, λ2, λ3 and τ were modeled as (Fe)1(Hf,Nb)2, (Fe,Hf,Nb)2(Fe,Hf,Nb)1, (Fe)2(Hf)1, (Fe)2(Hf,Nb)1, and (Fe,Hf,Nb)1(Fe,Hf,Nb)1 by a two-sublattice model, respectively. μ was described as (Fe,Hf,Nb)1(Hf,Nb)4(Fe,Hf,Nb)2(Fe,Hf,Nb)6 by a four-sublattice model. A set of self-consistent thermodynamic parameters of the Fe–Hf–Nb system was obtained.

Threshold Switching in Forming-Free Anodic Memristors Grown on Hf-Nb Combinatorial Thin-Film Alloys.

The development of novel materials with coexisting volatile threshold and non-volatile memristive switching is crucial for neuromorphic applications. Hence, the aim of this work was to investigate the memristive properties of oxides in a Hf-Nb thin-film combinatorial system deposited by sputtering on Si substrates. The active layer was grown anodically on each Hf-Nb alloy from the library, whereas Pt electrodes were deposited as the top electrodes. The devices grown on Hf-45 at.% Nb alloys showed improved memristive performances reaching resistive state ratios up to a few orders of magnitude and achieving multi-level switching behavior while consuming low power in comparison with memristors grown on pure metals. The coexistence of threshold and resistive switching is dependent upon the current compliance regime applied during memristive studies. Such behaviors were explained by the structure of the mixed oxides investigated by TEM and XPS. The mixed oxides, with HfO2 crystallites embedded in quasi amorphous and stoichiometrically non-uniform Nb oxide regions, were found to be favorable for the formation of conductive filaments as a necessary step toward memristive behavior. Finally, metal-insulator-metal structures grown on the respective alloys can be considered as relevant candidates for the future fabrication of anodic high-density in-memory computing systems for neuromorphic applications.

Direct selective laser sintering of high-entropy carbide ceramics

The direct selective laser sintering (SLS) process was successfully demonstrated for additive manufacturing of high-entropy carbide ceramics (HECC), in which a Yb fiber laser was employed for ultrafast (in seconds) reactive sintering of HECC specimens from a powder mixture of constitute monocarbides. A single-phase non-equiatomic HECC was successfully formed in the 4-HECC specimen with a uniform distribution of Zr, Nb, Hf, Ta, and C. In contrast, a three-layer microstructure was formed in the 5-HECC specimen with five metal elements (Zr, Nb, Hf, Ta and Ti), consisting of a TiC-rich top layer, a Zr–Hf–C enriched intermediate layer, and a non-equiatomic Zr–Ta–Nb–Hf–C HECC layer. Vickers hardness of 4- and 5-HECC specimens were 22.2 and 21.8 GPa, respectively, on the surface. These findings have important implications on the fundamental mechanisms governing interactions between laser and monocarbide powders to form a solid solution of HECCs during SLS.Graphical abstract

Martensitic transformation and shape memory effect of TiZrHf-based multicomponent alloys

Novel superelastic alloys and shape memory alloys composed of multi-principal elements with non-toxic and low magnetic susceptibility were developed. Phase constitution, crystallographic characteristics, mechanical properties, superelasticity and shape memory effect were investigated in Ti–Zr–Hf–Nb–Sn alloys. According to X-ray measurements, compositions exhibiting β phase, α’ phase and α” phase were determined. The lattice parameters of the phases were also determined. Lattice deformation strains were calculated based on the lattice parameters. The Ti–Zr–Hf–Nb–Sn alloys exhibited high tensile strength in a range of 600–1000 MPa. Superelasticity and shape memory effect due to β→α” martensitic transformation and the reverse transformation were observed in the Ti–Zr–Hf–Nb–Sn alloys. Superelastic recovery strain of 2.1% was observed in a (TiZrHf)–8.5Nb–3Sn alloy. The (TiZrHf)–8.5Nb–3Sn alloy exhibited low magnetic susceptibility comparing with alloys applied in medical fields. Potential of large superelastic recovery strain of the alloys was discussed based on the crystallographic and microstructural characteristics.

Activation characterization of a novel quinary alloy Ti-Zr-V-Hf-Nb non-evaporable getters by x-ray photoelectron spectroscopy.

The first results on the activation process and mechanisms of novel quinary alloy Ti-Zr-V-Hf-Nb non-evaporable getter (NEG) film coatings with copper substrates were presented. About 1.075 µm of Ti-Zr-V-Hf-Nb NEG film coating was deposited on the copper substrates by using the DC sputtering method. The NEG activation at 100, 150, and 180 °C, respectively, for 2 h was in situ characterized by x-ray photoelectron spectroscopy (XPS). The as-deposited NEG film mainly comprised the high valence state metallic oxides and the sub-oxides, as well as a small number of metals. The in situ XPS studies indicated that the concentrations of the high-oxidized states of Ti, Zr, V, Hf, and Nb gradually decreased and that of the lower valence metallic oxides and metallic states increased in steps, when the activation temperature increased from 100 to 180 °C. This outcome manifested that these novel quinary alloy Ti-Zr-V-Hf-Nb NEG film coatings could be activated and used for producing ultra-high vacuum.

High‐entropy boride–carbide ceramics by sequential boro/carbothermal synthesis

AbstractA dual‐phase high‐entropy boride (HEB)/carbide (HEC) ceramic with a fine grain size was synthesized by a sequential boro/carbothermal process. In the first step, an Hf–Nb–Ta–Ti–Zr‐containing carbide was synthesized by a carbothermal reduction of oxides followed by the reaction of the carbide with B4C and ZrH2 to convert part of the carbide to boride. The resulting composition was ∼29 vol% HEB with an average grain size of ∼1.1 μm. Solid solution formation occurred at the densification temperature of 1900°C resulting in a relative density higher than 99%. The Vickers hardness was 26.5 ± 1.4 GPa. This is the first report of synthesizing dual‐phase boride–carbide high‐entropy ceramics from carbothermally synthesized, HEC powders.

Experimental determination of isothermal sections of the Hf–Nb–Ni system at 950 and 1100°C

AbstractThe complete isothermal sections of the Hf–Nb–Ni system at 950 and 1100 °C were constructed, in which the phase constituents and compositions of alloy samples were determined by scanning electron microscopy with energy dispersive X-ray spectroscopy, and X-ray diffraction. Nine three-phase regions at 950 °C and nine three-phase regions at 1100 °C were confirmed. Four three-phase regions at 950 °C and five three-phase regions at 1100 °C were proposed. The solid solubilities of third components in the binary compounds were determined. A new ternary compound τ with Hf2Rh structure was found.

Ti–Zr–Hf–Nb–Ta–Sn high-entropy alloys with good properties as potential biomaterials

Ti–Zr–Hf–Nb–Ta–Sn high-entropy alloys with good properties as potential biomaterials