Zr-Ni Metallic Glasses Research Articles

Atomistic simulation of a NiZr model metallic glass under hydrostatic pressure

Compressive behavior of a model NiZr metallic glass under hydrostatic pressure is simulated using molecular dynamics. The equation of state obtained exhibits two distinct regimes, one at low and the other at high pressure, along with an intermediate region in between. The densification is associated with topological rearrangement of atoms at low pressure and hard-sphere-like compaction dictated by the strong interatomic repulsion at high pressure. Different from many isotropic materials, the atomic rearrangement in the metallic glass during compression is accompanied by strong local topological structure change and chemical short-range (re)ordering. The possibility of a pressure-induced phase transition is briefly discussed.

Ordered clusters and free volume in a Zr–Ni metallic glass

The atomic arrangement of a model metallic glass Zr2Ni was studied by extended x-ray absorption fine structure and x-ray scattering experiments combined with reverse Monte Carlo simulation imposed an additional potential constraint. By an approach to calculating the free volume (FV) on atomic level, we have found a connection between the coordination number and FV, and then revealed that the atomic structure of Zr2Ni metallic glass is essentially an association of the ordered clusters and FV. The ordered clusters about 1.5nm consist of a densely packed core (i.e., icosahedral or fcc-type packing) and the surrounding loosely packed clusters with large FV.

Identification and Characterization of Potential Shear Transformation Zones in Metallic Glasses

The stability of local atomic configurations in a Ni-Zr metallic glass is studied by molecular dynamics. It is shown that individual atom displacements induce irreversible atomic rearrangements under different glass relaxation, temperature, and strain conditions. The number of regions with an unstable topology depends on the glass relaxation degree. Their time evolution is governed by thermal activation, the activation energy decreasing with elastic strain. It is also shown that unstable regions are located in correspondence of shear transformation zones operating under plastic deformation.

Voronoi Analysis of the Structure of Ni-Zr-Al Ternary Metallic Glass

Ni-Zr metallic glasses have been recognized to be unstable in comparison with Cu-Zr metallic glasses. An analysis of Voronoi polyhedra in the RMC simulations based on the diffraction data could characterize the atomic configurations around Ni and Cu atoms. The polyhedra around Ni atoms are dominated by trigonal prism-like, Archimedian antiprism-like, and similar polyhedra. In contrast, icosahedron-like polyhedra are preferred for Cu. The Ni-Zr glasses have been reported to stabilize by adding Al. Therefore, in this work, the analysis of Voronoi polyhedra around Ni, Zr and Al atoms for Ni25Zr60Al15 ternary metallic glass was carried out in order to clarify the difference between the atomic structures for the binary and ternary metallic glasses. Trigonal prism-like, Archimedian antiprism-like and similar polyhedra, which are dominated in the Ni-Zr metallic glasses, decreased in number by adding Al to the Ni-Zr system. On the contrary, the number of icosahedron-like polyhedra was found to increase. The results apparently indicate that the addition of Al into Ni-Zr binary system promote the formation of icosahedron-like polyhedra in the structure. Therefore, from these results, we can easily recognize that icosahedron-like polyhedra play an important role to stabilize the structure of metallic glasses.

Effect of Pr addition on glass-forming ability of Al–Ni–Zr metallic glass alloy

Metallic glass alloys of Al 84Ni 12Zr 4− x Pr x ( x = 0–3) were prepared by melt-spinning technique. Thermal stability and amorphous nature were investigated in Al 84Ni 12Zr 4− x Pr x ( x = 0–4) alloys with X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Results show that appropriate Pr addition promotes the GFA of this alloy system while declines the thermal stability. It also can be seen from the results that the total area of exothermic peaks shows good correlation with GFA. The less total area of exothermic peaks is, the better GFA of Al 84Ni 12Zr (4− x) Pr x ( x = 0–3) system is.

Voronoi analysis of the structure of Cu–Zr and Ni–Zr metallic glasses

The structures of Cu–Zr and Ni–Zr metallic glasses have been studied by neutron diffraction and Reverse Monte Carlo (RMC) modeling. A pre-peak at Q∼17 nm −1 was observed in the structure factor, S( Q), of Ni–Zr metallic glasses, and this is associated with the Ni–Ni partial structure factor was well reproduced by the RMC modeling. An analysis of Voronoi polyhedra in the RMC simulations was used to characterise the different atomic configurations around Zr, Ni and Cu atoms. The Zr environments are very similar in the two systems, but there are marked differences between the polyhedra around Ni and Cu atoms. The polyhedra around Ni atoms are dominated by trigonal prismatic-like, Archimedian antiprismatic-like, and similar polyhedra, with smaller total coordination numbers less than 10. In contrast, icosahedron-like polyhedra with total coordination numbers in excess of 11 are preferred for Cu.

Structural Observation and RMC Modeling for Ni-Zr and Cu-Zr Metallic Glasses

Structural Observation and RMC Modeling for Ni-Zr and Cu-Zr Metallic Glasses

Effect of Al on Local Structures of Zr–Ni and Zr–Cu Metallic Glasses

In order to investigate the role of Al on the thermal stability of supercooled liquid state, the local structures of Zr70M30 and Zr70M20Al10 (M=Ni, Cu) metallic glasses have been studied by the X-ray diffraction and EXAFS measurements. It is found that the different effect of Al substitution on the local structures around Cu and Ni elements is exhibited. No characteristic change is observed in the local structure in the Zr–Cu metallic glass by Al substitution, whereas a drastic change in the environment around Ni atom can be confirmed in the Zr–Ni metallic glass. That is, the coordination number of Zr around Ni decreases significantly by substitution of Al in the Zr–Ni metallic glass. This would be caused by the preferential correlation between Al and Zr. This result suggests that Al plays a dominant role on the formation of novel local structure with a decomposition of the tetragonal Zr2Ni-like local environment in the Zr–Ni binary alloy. We conclude that the novel local structure contributes to the stability of the supercooled liquid state in the Zr–Al–Ni metallic glass.

A molecular dynamics study on the role of localised lattice distortions in the formation of Ni–Zr metallic glasses

The formation of Ni–Zr binary metallic glasses resulting from the introduction of localised crystalline lattice distortions is investigated by means of constant-temperature, constant-pressure molecular dynamics simulations. Substitutional solid solutions of various composition were created by inserting substitutional atoms into a pure lattice. The insertion of Zr atoms into the regular Ni lattice determined its volume expansion, while the insertion of Ni atoms into the Zr lattice induced a volume contraction. Local lattice distortions are associated with substitutional atoms due to the size mismatch between Ni and Zr. The radial distribution functions, the rms atomic displacement and the static order parameter are used to characterise the response of the system to the insertion of substitutional atoms. The gradual loss of crystalline long-range order is accompanied by a large elastic softening. It appears that the static order parameter represents the fundamental quantity to characterise the elastic behaviour of both Ni- and Zr-based solid solutions.

Correlation of electronic structure and catalytic activity of Zr–Ni amorphous alloys for the hydrogen evolution reaction

The electrocatalytic activity of amorphous Zr–Ni alloys with respect to the hydrogen evolution reaction (h.e.r.) was studied in relation to both composition and active surface area. Kinetic parameters of the h.e.r. were evaluated by electrochemical and impedance spectroscopy techniques in 1-M NaOH solution at room temperature. Intrinsic activity of the investigated metallic glasses was related to the real exchange current density, j 0 and the reciprocal value of charge transfer resistance, R ct −1. The surface roughness factor was deduced from impedance measurements. Electrocatalytic activity of two investigated Zr 100− y Ni y alloys, with y=33; and y=60 was directly related to the split-band electronic structure of Zr–Ni alloys. An enhanced electrocatalytic activity observed for the h.e.r. with increasing y in the Zr–Ni alloy was associated with a rapid increase of electronic density of states at Fermi energy level, D ( E F) of the 3d Ni band with increasing Ni concentration. The formation of Ni-hydrides during hydrogen evolution was prevented and the high activity of the 3d Ni band for the h.e.r. was preserved. It was shown that alloying of Zr–Ni metallic glasses with varying individual component contents could be explored to optimize the electrocatalytic properties of Zr–Ni glasses and their use in water electrolysis, as electrode materials of long term stability. The highest catalytic activity could be expected for y=65, when a maximum hybridization of 3d–4d orbitals and a rapid decrease i.e. minimum density of 4d Zr states at the Fermi level were observed.

Diffusion Enhancement in Glassy Metals Under Non-Equilibrium Conditions

AbstractThe diffusion properties of a Ni-Zr metallic glass formed at the interface of a bulk diffusion couple have been studied in conditions far from a fully relaxed state. The growth kinetics of the interface film have been enhanced by both plastic deformation and high energy electron irradiation. Different results have been obtained in the two cases, since in the first case the film grows exponentially with time, while in the second case the usual square root dependence on time is observed. This behaviour has been interpreted as a consequence of the annihilation kinetics of the excess free volume introduced in the glass by the above methods. Two different mechanisms of free volume annihilation , namely exchange with a crystal vacancy at the glass-crystal interface and structural relaxation in the bulk glassy phase have been considered to be operative so that the nature of the growth kinetics has been found to depend on the mechanism predominant in each experimental condition.

Radiation-enhanced diffusion in amorphous Ni-Zr studied by in situ electron irradiation in a transmission electron microscope.

Radiation-enhanced diffusion (RED) in a Ni-Zr metallic glass has been studied by high-energy electron irradiation performed in situ in a transmission electron microscope. Irradiations have been carried out on thin foil cross-sectional specimens obtained from Ni-Zr bulk diffusion couples. The diffusivity under electron irradiation has been derived from the growth rate of a thin Ni-Zr amorphous film present at the Ni-Zr interface. Experimental results show that the Ni is the most mobile species in these experimental conditions and that radiation damage occurs in glassy metals at a lower electron energy relative to the corresponding crystalline compound. Moreover, the dose-rate sensitivity of RED appears to depend also on the energy of the electron beam. To explain this effect, the process of radiation displacement in metallic glasses has been modeled within the framework of the free-volume theory of the structure of metallic glasses. The results of this simple model can qualitatively explain our results as well as those relative to RED induced by high-energy ion irradiation.

Comment on "Weak-localization and Coulomb-interaction effects in hydrogen-doped Zr-Ni and Zr-Cu metallic glasses"

Comment on "Weak-localization and Coulomb-interaction effects in hydrogen-doped Zr-Ni and Zr-Cu metallic glasses"

A TEM study of the microstructures formed during the crystallization of Ni–Zr metallic glasses

The microstructure of two metastable crystalline phases, which are formed during the first step of the crystallization process in Ni–Zr metallic glasses, was investigated by transmission electron microscopy. For the composition Ni33Zr67, crystallites with average size of 150 nm having the face-centered cubic E93 structure are formed. For the Ni42Zr58 composition, 100 nm size crystallites with a simple cubic unit cell, space group Pa3 are formed. The microstructure of the crystallites in the early stage of crystallization of the two phases is similar to globular morphology and internal striations.

Low-temperature specific heat of V-substituted NiZr(V) metallic glass

Low-temperature (1.7 ∼ 5.5K) specific heat measurements are reported for four series of seventeen metallic glasses, Ni 100−xZr x (x=50∼75), (Ni .33Zr .67) 100−xV x, (Ni .50Zr .50) 100−xV x and (Ni .67Zr .33) 100−xV x (x=10∼25), in order to study the effect of V (3d metal) substituted for Zr (4d metal) on NiZr metallic glasses in terms of the electronic structure near the Fermi energy E F. Each set of C/T vs T 2 plot has been fitted to the equation C = γ T+ β T 3+ δ T 5 except for the binary alloy, showing the superconducting transition above 1.7 K. It is found that the electronic specific heat coefficient γ increases with increasing V content and the rate of increase Δ γ per V content is also an increasing function of Ni content. The results are attributed to the fact that the height of the electronic density of states at E F almost arising from the early transition metal increases due to the stronger localization of 3d and the new bonding states between Ni and V are enhanced with increasing Ni content. This latter character is consistent with the variation of the short range order parameter of NiZr pairs on Ni content for the same NiZr(V) metallic glasses.

Evidence for electron — electron interaction and localization effects in the magnetic susceptibility of hydrogen — doped ZrNi metallic glass

Measurements of the magnetic susceptibility in the temperature range from 2K to 300K are reported for paramagnetic ZrNi metallic glass doped with hydrogen. Observed anomalous temperature dependence of the magnetic susceptibility is interpreted in terms of corrections in the electronic density of states at the Fermi level, which are due to interaction effects in disordered three-dimensional conductors. Hydrogen is found to influence strongly the quantum mechanical interference at defects, thus slowing down the spin diffusion and enhancing the susceptibility at low temperatures.

Resistivity and Hall effect in sputtered NiZr metallic glasses

Films of Ni1−xZrx metallic glasses have been prepared by sputter deposition over the composition range 0.1<x<0.86. In this paper we present data on the composition and temperature dependencies of the resistivity and the Hall coefficient from 77 to 300 K. Where applicable, both the resistivity and the Hall coefficient closely follow the values reported for melt-spun glasses of the same composition. The Hall coefficient changes sign from positive to negative with decreasing x; for x<0.4 it also becomes increasingly temperature dependent (dRH/dT>0). Both the change in sign and the temperature dependence can be understood within the framework of an important extraordinary contribution to the Hall coefficient for these paramagnetic alloys.

Host and hydrogen diffusion in an NiZr metallic glass

Anelastic relaxation measurements have been used to study atomic mobility in glassy Ni 40Zr 60, before and after the introuction of hydrogen to the level [ H]/[ M] = 0.78. By the combined use of the long-range Gorsky relaxation and the short-range reorientation relaxation, the motion of hydrogen has been observed over an extended temperature range and found to deviate from Arrhenius behavior below 140 K. The distribution of reorientation relaxation times is approximately log-normal, with a single maximum whose width increases to 5 decades at 100 K. The introduction of hydrogen has been found to accelerate relaxation behavior associated with the motion of host atoms. This represents a new effect, termed hydrogen-enhanced host diffusion.

Crystallization of Zr-Ni metallic glasses

In a previous paper the results of a study of the crystallization of Zr-Ni metallic glasses of compositions between 55 and 70 at. % Zr were reported. Data from differential scanning calorimetry (DSC) and x-ray diffraction (XRD) were presented and discussed with respect to the phase transformations occurring during the crystallization process. A metastable crystalline phase, shown by DSC and XRD results to appear between 57 and 63.2 at. % Zr, was the first phase to appear upon heating the amorphous metal. (Evidence indicates the stoichiometric composition for this phase is approximately 60% Zr.) This metastable phase transforms to the equilibrium crystalline phases (ZrNi and Zr2Ni) upon further heating. For compositions of 55-57 and 63.5-70% Zr only the equilibrium phases appear upon heating. It was noted that phase separation and chemical short range ordering (SRO) are believed to play an important role in the crystallization of these alloys.

STRUCTURAL STUDIES OF AMORPHOUS HYDROGEN STORAGE ZrNi-ALLOYS

In this article the effect of hydrogen on structure of amorphous alloys of the form Ni0.243Zr0.757 Hy 0≤y≤0.25 is reported. The results of investigations on the structure of amorphous Ni0.243Zr0.757 and its hydrogenated sample are described. X-ray diffraction data are employed to calculate their radial distribution functions (RDF(r)) structures. The coordination umber of Ni-Zr metallic glass is determined as 10.6 and the hydrogen atoms in the hydrogenated amorphous Ni0.243Zr0.757H0.25 apparently prefer to occupy the tetrahedral hole surrounded mainly by 4 Zr atoms and a few by 3 Zr + 1 Ni atoms.