Ni Nb Metallic Glass Research Articles

Study on the structural origins of glass-forming ability and crystallization behaviors in Ni[sbnd]Nb binary alloys

The limited glass forming ability (GFA) poses a pervasive challenge in different metallic glass (MG) systems. This study systematically investigated the GFA of NiNb binary alloys, particularly those near the eutectic composition, aiming to explore the intrinsic factors contributing to the disparities in GFA among NiNb binary MGs. The relationship between liquid-like atomic structures and resistance to devitrification is thoroughly examined through the application of k-nearest neighbor machine learning methods. The results indicate that the critical diameter of Ni61Nb39, Ni61.5Nb38.5, and Ni62Nb38 MGs reaches upto 2 mm. An amorphous-amorphous transition is discerned within NiNb MGs exhibiting superior GFAs. These alloys exhibit low thermodynamic driving forces for crystallization, resulting in correspondingly elevated fragility coefficients. Furthermore, the presence of icosahedral-like clusters and the probability density of crystal-like clusters are observed to be intricately linked to GFA and the resistance to crystallization in NiNb MGs. The heightened abundance of crystal-like clusters within the liquid-like domain renders the alloy more susceptible to crystallization. Concurrently, icosahedral-like ordered clusters exert a “pinning effect” on the crystal-like regions, effectively inhibiting crystallization. These results collectively shed light on the fundamental nature of glass formation in NiNb binary MGs.

Exploration of the icosahedral clusters in Ni–Nb binary metallic glasses via first-principles theory

The binding energy, chemical ordering parameters, and electronic structure of Ni-centered NinNb13−n(n = 6, 7, 8, 9) icosahedral clusters were studied in accordance with the first-principles theory. These calculations demonstrated that the binding energy of the icosahedral clusters decreased when the homogeneous shell atoms preferred to bond together. The density of state at the EF of most icosahedral clusters was near a gap, indicating that all icosahedral clusters were in a relatively stable state. For the icosahedral cluster, the states near the Fermi level were dominated by Ni- and Nb-d electrons. The electron-localization function analysis of the most stable and unstable structures in icosahedral clusters showed that chemical bonding favored the formation of icosahedral clusters by introducing a string-like or net-like structure and further stabilized icosahedral clusters. The origin of glass-forming ability (GFA) was the synergistic effect of electronic stability and topological stability of icosahedral clusters in Ni–Nb metallic glasses.

Structural origin of the enhancement in glass-forming ability of binary Ni-Nb metallic glasses

This study aimed to clarify the structural origin of the enhancement in glass-forming ability (GFA) of binary Ni-Nb metallic glasses (MGs). The atomic structures of NixNb100-x(x=50, 59.5, 62.5, 70) alloys were systematically studied using synchrotron total-scattering method and molecular dynamics calculation. The classical molecular dynamics simulations results agree well with the experiments. Ni62.5Nb37.5 alloy has the best glass-forming ability and the densest atomic-packing structure among the four components. The larger fraction of full icosahedron <0, 0, 12, 0> and distorted icosahedron <0, 2, 8, 2> clusters implied that the relatively better GFA was near Ni62.5Nb37.5. Intercross-sharing icosahedral medium-range orders superclusters composed of 2–16 icosahedra interpenetrated at 900 K. The glass structure in Ni62.5Nb37.5 MG was a heterogeneous mixture of interpenetrating icosahedral clusters, forming a chain-like network structure in the matrix. These Ni-centered icosahedra polyhedra, with their high packing density and low mobility, led to high-density atomic packing and slow dynamics, thereby playing an essential role in controlling GFA.

Anisotropic and size-dependent mechanical responses of free-standing Ni-Nb metallic glass thin film

Via in-situ tensile test, we demonstrated a brittle-to-ductile transition of Ni-Nb metallic glass (MG) thin films when the film thickness decreased from 363 nm to 87 nm. The elastic strain limit of 4.7% and apparent work hardening behavior were seen for free-standing 87 nm-thick film. Contrary to quenched MGs, anisotropic mechanical response existed in MG thin films with nanocolumnar structure owing to the deteriorated bonding strength of column boundaries.

Corrosion protection of NiNb metallic glass coatings for 316SS by magnetron sputtering

Metallic glasses (MGs) appear as promising anti-corrosion coating materials due to their microstructural and physicochemical advantages. Herein, we proposed magnetron sputtered NiNb thin film MG coatings (MGCs) with different structures and compositions for corrosion protection of 316 stainless steel in an aggressive saline environment. The properties of monolayered Ni50Nb50 and Ni60Nb40, as well as the multilayered Ni50Nb50/Ni60Nb40 (at.%) MGCs, were characterized in terms of morphology and microstructural properties, as well as the anticorrosion behavior. All the NiNb MGCs presented compact structure and the monolayered coatings exhibited preferable adhesion properties in comparison with the multilayered coating. The electrochemical tests and XPS results imply that the monolayered Ni50Nb50 MGC with high Nb content resisted corrosion mainly due to the formation of stable passive film that contained abundant Nb2O5 species, whereas the Ni60Nb40 MGC with high Ni content showed week corrosion protection performance during long-term service due to the dissolution of Ni cations and the devastation of the coating structure. Though with bit worse adhesion and more vulnerable Ni60Nb40 layers, the multilayered Ni50Nb50/Ni60Nb40 MGC possessed comparable corrosion resistance with the monolayered Ni50Nb50 MG coating, which remained stable even after 32 days of exposure. Such performance should be ascribed to the combined eff ;ect of the repassivation property for the sub-layers, the hindrance of propagation paths of micro-defects, and the obstruction of corrosive species by interfaces in the multilayered coating.

Tailoring nanostructured Ni-Nb metallic glassy thin films by substrate temperature

Improving the thermostability and mechanical properties of metastable amorphous materials are critical for their potential applications. Here we report the achievement of a wide variety of nanostructures and properties in Ni-Nb metallic glass thin films (MGTFs) by tuning the substrate temperature (Tsub) during magnetron sputtering. By gradually increasing Tsub close to glass transition temperature (Tg) from room temperature, we evidence the transition from the hierarchical nanostructure with microcracks to the denser nanostructure with a smoother surface and smaller column/particle size. This transition contributes to the enhanced plastic deformation stability and nanomechanical properties, thermal stability, and optical reflectivity in the visible light wavelength. We explain the nanostructure evolution with Tsub based on the competition between the shadowing effect and surface diffusion. The shadowing effect is dominant in low-Tsub films and promotes the voided boundaries, while surface diffusion is remarkably enhanced at high Tsub (0.76–0.87 Tg) to form dense intergrain boundaries. This finding provides a promising avenue towards producing novel functional MGTFs with controllable nanostructures and properties without any post-treatment.

Contribution of Nb towards enhancement of glass forming ability and plasticity of Ni-Nb binary metallic glass

In this present study, effect of Nb content on glass forming ability and plasticity of Ni-Nb metallic glass has been investigated using molecular dynamics simulation with embedded atom method (EAM). Ni-Nb metallic glass specimens having different atomic percentages of Nb content (i.e. ~15, 20, 25, 30, 38, 40.5, 45 and 50at.%) are prepared by fast cooling process (cooling rate~1012Ks−1) from their liquid phase. It is observed that increase in Nb content up till 38at.% causes improvement of glass forming ability of Ni-Nb binary system. On further increment of Nb content, glass forming ability is found to be slightly reduced or remain almost same. Voronoi cluster analysis has been performed to evaluate the variation in short range ordering with increasing Nb content in Ni-Nb glass. Simulated tensile tests are also performed, and it reveals that higher Nb content actually helps in augmentation of the plastic behavior of the Ni-Nb metallic glass.

Nanoindentation study of size effect on shear transformation zone size in a Ni–Nb metallic glass

An apparent reduction in both size and amount of shear bands was observed, as the sample converted from 45μm ribbon to 1.8μm film in a Ni–Nb metallic glass. Such size effect on the macroscopic plastic characteristic could be intrinsically related to the scale variation of the shear transformation zone (STZ). Statistical analysis of the maximum shear stress, which is based on the distribution of first pop-in events in nanoindentation, was employed to estimate the STZ volume and atoms it contains. The result indicates that the STZ size decreases from 83 atoms in the ribbon to 36 atoms in the film. This phenomenon was consistent with the result by another experimental method based on the strain rate sensitivity (SRS). Upon nanoindentation creep test, STZ sizes with 44 atoms and 18 atoms were calculated for the ribbon and film, respectively. The variation trend of the STZ size was discussed in terms of free volume content combined with internal stress which arises during the film deposition and the local atomic structure changes recognized by EXAFS measurement.

Atomic and electronic structure of Ni-Nb metallic glasses

Solid state 93Nb nuclear magnetic resonance spectroscopy has been employed to investigate the atomic and electronic structures in Ni-Nb based metallic glass (MG) model system. 93Nb nuclear magnetic resonance (NMR) isotropic metallic shift of Ni60Nb35Sn5 has been found to be ∼100 ppm lower than that of Ni60Nb35Zr5 MG, which is correlated with their intrinsic fracture toughness. The evolution of 93Nb NMR isotropic metallic shifts upon alloying is clearly an electronic origin, as revealed by both local hyperfine fields analysis and first-principle computations. This preliminary result indicates that, in addition to geometrical considerations, atomic form factors should be taken into a description of atomic structures for better understanding the mechanical behaviors of MGs.

Super elastic strain limit in metallic glass films

On monolithic Ni-Nb metallic glass films, we experimentally revealed 6.6% elastic strain limit by in-situ transmission electron microscopy observations. The origin of high elastic strain limit may link with high free volume in the film, causing the rearrangement of loosely bonded atomic clusters (or atoms) upon elastic deformation. This high elastic limit of metallic glass films will shed light on new application fields for metallic glasses, and also trigger more studies for deformation mechanism of amorphous materials in general.

Pit growth in a Ni–Nb metallic glass compared with its crystalline counterpart

The growth and repassivation behavior of metastable pits in a Ni50Nb50 metallic glass, as well as its crystalline counterpart, were investigated by statistical analysis on the current transients in potentiostatic measurements. The results show that amorphous Ni50Nb50 sample demonstrates a higher transient current, shorter pit growth and repassivation times than the crystallized sample. Comparisons of pit growth rates and charges passed during pitting reveal that pits in amorphous alloy grow faster but with smaller final pit volumes. It is suggested that amorphous structure can induce rapid dissolution in pits and thus promote the accumulation of passivating elements (Nb), resulting in a higher repassivation rate. A notable effect of amorphous structure on the early growth of pits is determined.

Structure inhibited pit initiation in a Ni–Nb metallic glass

A model metallic glass Ni 50Nb 50, which would undergo a polymorphous transformation during devitrification, was selected to clarify the correlation of amorphous structure with corrosion. The electrochemical polarization behaviour, film breakdown and composition of surface film have been studied in detail by comparing the amorphous alloy with its crystalline counterparts. Interestingly, it was found that the pit initiation is inhibited greatly on amorphous sample relative to the crystallized one. The origin is thought to be related to the defective interface beneath passive film that inhibits the formation of pitting precursors in corrosion.

Distinct atomic structures of the Ni-Nb metallic glasses formed by ion beam mixing

Four Ni-Nb metallic glasses are obtained by ion beam mixing and their compositions are measured to be Ni77Nb23, Ni55Nb45, Ni31Nb69, and Ni15Nb85, respectively, suggesting that a composition range of 23–85 at. % of Nb is favored for metallic glass formation in the Ni-Nb system. Interestingly, diffraction analyses show that the structure of the Nb-based Ni31Nb69 metallic glass is distinctly different from the structure of the Nb-based Ni15Nb85 metallic glass, as the respective amorphous halos are located at 2θ≈38 and 39 deg. To explore an atomic scale description of the Ni-Nb metallic glasses, an n-body Ni-Nb potential is first constructed with an aid of the ab initio calculations and then applied to perform the molecular dynamics simulation. Simulation results determine not only the intrinsic glass forming range of the Ni-Nb system to be within 20–85 at. % of Nb, but also the exact atomic positions in the Ni-Nb metallic glasses. Through a statistical analysis of the determined atomic positions, a new dominant local packing unit is found in the Ni15Nb85 metallic glass, i.e., an icositetrahedron with a coordination number to be around 14, while in Ni31Nb69 metallic glasses, the dominant local packing unit is an icosahedron with a coordination number to be around 12, which has been reported for the other metallic glasses. In fact, with increasing the irradiation dose, the Ni31Nb69 metallic glasses are formed through an intermediate state of face-centered-cubic-solid solution, whereas the Ni15Nb85 metallic glass is through an intermediate state of body-centered-cubic-solid solution, suggesting that the structures of the constituent metals play an important role in governing the structural characteristics of the resultant metallic glasses.

Fabrication and mechanical properties of Ni–Nb metallic glass particle-reinforced Al-based metal matrix composite

Ni70Nb30 metallic glass powders were prepared by mechanical alloying and subsequently combined with Al in order to form a metallic glass particle-reinforced Al-based metal matrix composite sintered below the melting temperature of Al by using the powder metallurgy method. The Young's modulus, yield strength and ultimate strength are all higher than for single-phase pure Al. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Microwave second-harmonic generation and point-contact spectroscopy of Ni–Nb metallic glasses

The point-contact spectra (the energy dependence of the amplitude of the second harmonic of the modulation current) of contacts of NixNb1−x metallic glasses are measured at audio (3726 Hz) and microwave (9.5 GHz) frequencies. It is established for the first time in rf dynamic experiments that the low-energy spectral feature due the scattering of electrons on two-level systems (TLSs) in the contact is observed at microwave frequencies as well. This is direct evidence of the existence of a fast relaxation process in the contacts, with a characteristic time τ≪10−10 s. There is also a small contribution from slower scattering processes. It is found that the videodetection signal contains a component due to a steady-state nonequilibrium occupation of the states of the TLSs under microwave irradiation. The coupling efficiency of the contact with the waveguide and rf receiver is estimated to be 5–7%. A slight minimum of the resistance at zero voltage observed for some of the contacts is attributed to superconducting fluctuations of the order parameter at a temperature T∼2.3Tc.

TEM study of silicide islands formation in reactions of thin films of metallic glasses with Si substrates

The formation of silicide islands during solid-state reactions of thin films of Pd W, Pd Ta and Ni Nb metallic glasses with Si substrates was studied by transmission electron microscopy (TEM). Pd 2Si or NiSi 2 islands were found to grow epitaxially in Si as a result of Pd of Ni diffusion from amorphous metallic alloys. The crystallization of films results in the rapid increase of their diffusion inside the substrate, leading to an increase of Pd 2Si islands thicknesses which previously grew parallel to the film-Si interface. Silicide islands are mainly bounded inside the substrate by Si(111) planes. Some islands (“negative”) were observed to dissolve with time showing the change of the reaction direction. This fact is explained by the possible change of the sign of the Gibbs energy variation ΔT during interface reactions of amorphous metallic films with Si. Some “negative” Pd 2Si islands were observed to move during reactions forming channels parallel to film-Si interfaces.

Model Calculations of the Structure of Ni-Nb Metallic Glasses

Abstract The partial pair correlation functions of amorphous NixNb100-x alloys (x = 40, 50, 56, and 63) were simulated by computer modelling. A Cluster Relaxation procedure yielded reasonable agree­ ment with the experimental functions when non-additive pair potentials with preference for Ni-Nb atomic pairs were applied. With the use of the Reverse Monte Carlo method perfect agreement could be achieved. The impact of the chemical effect on the short range order is discussed by comparison with a statistical reference cluster. The analysis of the model clusters showed that the chemical short range order effect in amorphous Ni-Nb alloys, increasing with the Ni concentration, does not in­ volve specific stereochemical atomic arrangements. There is no correspondence to the short range order in crystalline Ni3Nb. The structure of Ni-Nb metallic glasses can be described as a polytetra-hedral packing with preferred hetero-coordination.

Onset of crystallization of Ni-Nb metallic glasses

Etude des verres de systemes Ni 100 .− x Nb x a 40%≤x≤60% du point de vue de la stabilite et homogeneite de l'etat amorphe durant le recuit sous atmosphere d'argon a des temperatures comprises entre 873 et 973 K