Binary Amorphous Alloys Research Articles

Dense Kondo behavior in the electric resistivity and the specific heat of amorphous [formula omitted] alloy

Binary amorphous alloy system Ce x Mn 100 - x shows the dense Kondo behavior in the Ce-rich side. This fact is confirmed by the large T 2 coefficient A of electrical resistivity at low temperature and also the large linear specific heat coefficient γ . The result of log A versus log γ 2 plot for Ce-rich samples shows the systematic change, but deviates from the Kadowaki–Woods (KW) relation. If we take the orbital degeneracy of Ce 4f-electron into account, according to Kontani's recent analysis, the result satisfies the generalized KW-relation. Therefore, present amorphous Ce–Mn alloy seems to form the dense Kondo state or the heavy-fermion state at low temperature.

Hydrogen Permeation of the Melt-Spun Ni–X–Zr Amorphous Membranes

The Ni 7 0 - x / 2 Nb 3 0 - x / 2 Zr x (x = 10, 20, 30, 40 and 60 at%) amorphous alloys were prepared by the melt-spinning technique. The hydrogen permeability of those alloys was compared to derive the principles of the element addition. As the result, it was found that the hydrogen permeability of the Ni-Nb-Zr ternary amorphous alloys increases with increasing Zr content. However, the hydrogen permeation of the Ni 4 0 Zr 6 0 binary amorphous alloy was much smaller than that of the Ni 5 0 Nb 1 0 Zr 4 0 amorphous alloy. This behavior indicates that the Nb addition also improves the hydrogen permeability. Then, as a next step, we prepared the Ni-X-Zr (X = Y, Ti, Hf, V, Nb and Ta) amorphous alloys to investigate the effect of the additional elements on the hydrogen permeation of melt-spun Ni-Zr binary amorphous alloys. As the result, it was found that the additional element with higher hydrogen affinity was preferable and that the Ni content should be reduced to improve the permeability.

Local Structure and Glass Transition in Zr-Based Binary Amorphous Alloys

The physical significance of the glass transition observed by differential scanning calorimetry (DSC) in the metallic glasses was considered through the measurements of the heating-rate, β, dependence of the glass transition temperature, Tg, and the crystallization temperature, T x , in the Zr 7 0 Cu 3 0 and Zr 7 Ni 3 0 amorphous alloys and X-ray study of their structures in as-quenched and crystallized states. Zr 7 0 Cu 3 0 exhibits the glass transition before crystallization, hut Zr 7 0 Ni 3 0 is immediately crystallized at heating rates of conventional time scale in the DSC measurement. The heating rate β c at the intersection of the two linear curves of T g and T x against log β provides us with a significant measure to determine the glass-forming ability or thermal stability of the metallic glasses. By heating at β larger than β c , the crystallization is suppressed and the glass transition is clearly observed even in Zr 7 0 Ni 3 0 . The thermal stability of the Zr 7 0 Cu 3 0 amorphous alloy is caused by retardation of crystallization due to the amorphous structure that is different from the Zr 2 Cu crystalline phase. In contrast, the thermal instability of Zr 7 0 Ni 3 0 is attributed to the structural similarity to the Zr 2 Ni crystalline phase. Thus, suppressing the crystallization is shown to be a key to enhance the thermal stability of the present amorphous alloys.

Bulk metallic glass formation in the binary Cu–Zr system

Using the Cu–Zr model system, we demonstrate that bulk amorphous alloys can be obtained by copper mold casting even in a binary metallic system. The narrow, off-eutectic, bulk-glass-forming range was found to require composition pinpointing to <1 at. %. A phase selection diagram is used to explain the success of our microstructure-based approach to pinpoint the best glass former in a given system. The implications of discovering simple binary bulk amorphous alloys are discussed, in terms of its impact on understanding the formation and physics of bulk metallic glasses.

Organization of Coordination Polyhedra in an Amorphous Binary Alloy

The local and intermediate structure of a simulated metal−metalloid glass-forming alloy is reported. The model, due to Kob and Andersen, has been the subject of considerable study in the context of the glass transition. In the A75B25 mixture the low-temperature coordination polyhedra about the B (“metalloid”) particles are dominated by geometries based on either the capped trigonal prism or the square antiprism. As the concentration of B particles increases from 0.25 to 0.5, the B coordination changes from regular 8- and 9-fold polyhedra to distorted and irregular 6- and 7-fold geometries.

Effect of covalent element boron on exchange interaction and magnetic moment in Fe0.4Gd0.6 binary alloy

Abstract Effect of covalent element of Boron (B) on magnetic properties such as exchange interaction and magnetic moment was studied for the simple ferrimagnet of Fe 0.4 Gd 0.6 binary amorphous alloy. In terms of molecular field analysis, the Fe magnetic moment decreases rapidly down to a half value by the introduction of 10 at% of B and the 2p electrons of B is considered to combine mainly with the 3d electrons of Fe. Further, the analysis reveals that the introduction of B causes the enhancement of J Fe–Gd by a factor of 2 and the reason for this can be attributed to the covalent bonding between B and Fe.

Plasticity in Nanocrystalline and Amorphous Metals: Similarities at the Atomic Scale

ABSTRACTFor metallic alloys, the amorphous state is often regarded as the limiting structure as grain size is reduced towards zero. One interesting consequence of this limit is that the properties of the finest nanocrystalline metals must begin to resemble those of metallic glasses. In this work we focus upon the nature of the plastic yield mechanisms in these material classes, and seek to identify commonalities and disparities in the nature of plastic yield in glasses and nanocrystals. The discussion is presented with reference to static atomistic simulations of (i) an amorphous binary alloy, and (ii) a nanocrystalline Ni specimen with grain size of 3 nm. We show that both these materials deform by the operation of fine atomic shearing events, and both exhibit asymmetric yielding as a consequence.

Effect of preparation conditions on the short-range order in Zr-based bulk glass-forming alloys

The short-range order in as-prepared and annealed Zr–Cu–Al–Ni glassy alloys, obtained by quenching from the melt at different cooling rates as well as by solid state reaction via mechanical alloying, was investigated by perturbed angular correlations technique (PAC). All the samples were also characterised by X-ray diffraction and differential scanning calorimetry. For all the as-prepared amorphous samples, the PAC spectra are well described by a Czjzek distribution revealing that the short-range order corresponds to that of a dense random packing of ions. The observed electric field gradient seems to be independent of the preparation method and, when compared with previous measurements, of the Zr content. These trends are discussed in comparison with the similar behaviour observed in binary amorphous alloys. Samples annealed above the glass transition temperature but below the crystallisation step showed two broad distributions of frequencies, which were assigned, to a metastable Ti 2Ni-type phase.

Nano icosahedral phase in Zr–Pd and Zr–Pt binary alloys

It was found that a nano icosahedral phase with a diameter less than 20 nm is formed as a primary crystalline phase in the melt-spun Zr 70Pd 30 and Zr 80Pt 20 binary amorphous alloys. The nano icosahedral phase is also formed in the as-quenched state in the Zr 80Pt 20 binary alloy by controlling the quenching rate. A slight redistribution of approximately 3 at% is observed during the quasicrystallization in the Zr 70Pd 30 alloy. In contrast, no significant compositional change between the nano icosahedral and residual amorphous phases is observed in the Zr 80Pt 20 alloy. The icosahedral medium-range order in the diameter range less than approximately 3 nm is observed in the high-resolution electron micrograph of the Zr 70Pd 30 amorphous alloy. It is suggested that the icosahedral quasicrystalline phase grows with assimilating the icosahedral medium-range order due to a slight redistribution of constitutional elements during quasicrystallization. The formation of the nano icosahedral phase in the Zr 70Pd 30 and Zr 80Pt 20 binary alloys seems to be attributed to the existence of the icosahedral medium-range order in the amorphous and/or liquid states.

The electrochemical hydriding properties of Mg–Ni–Zr amorphous alloy

The amorphous alloys of Mg–Ni–Zr were synthesized by mechanical alloying process, in which the effects of Zr addition were studied. A small shift of the broadening amorphous peak due to Zr additions was observed. The equilibrium hydriding pressure increased continuously with hydrogen contents in the amorphous alloys, while there was an obvious plateau pressure of 10 −4 MPa in the crystalline Mg 2Ni phase. The Zr addition lowered the equilibrium hydriding pressure and increased the hydrogen solubility from 1.4 wt% for Mg–Ni to 2.2 wt% for Mg–Ni–Zr. Accompanied by amorphization, the hydrogen discharge capacity increased largely, and reached 580 mA h / g for Mg–Ni–Zr alloy. The chronopotentiometric experiments were performed to investigate the hydrogen diffusion in the alloy powder in the high over-potential range. The diffusivity of hydrogen in the Zr-contained alloy was lower than the Mg–Ni binary amorphous alloy or in Mg 2Ni nanocrystalline alloy.

Nanoicosahedral quasicrystalline phase in Zr–Pd and Zr–Pt binary alloys

It is found that a nanoicosahedral phase in the diameter less than 20 nm is formed as a primary crystalline phase in the melt-spun Zr70Pd30 and Zr80Pt20 binary amorphous alloys. The nanoicosahedral phase is also formed in the as-quenched state in the Zr80Pt20 binary alloy by controlling the quenching rate. The slight redistribution of approximately 3 at % is observed during the quasicrystallization in the Zr70Pd30 alloy. In contrast, no significant compositional change between the nanoicosahedral and residual amorphous phases is observed in the Zr80Pt20 alloy. It is suggested that the precipitation of nanoicosahedral phase in the Zr70Pd30 alloy takes place by a diffusion-controlled growth mode accompanying an increase in nucleation rate. The activation energy for grain growth is calculated to be 270 kJ mol−1, which implies the growth of icosahedral phase without a long-range atomic redistribution. The icosahedral medium-range order in the diameter range less than ∼2 nm is observed in the high-resolution electron micrographs of the melt-spun Zr70Pd30 and Zr80Pt20 amorphous alloys. It is realized that the icosahedral quasicrystalline phase can grow easily with assimilating the icosahedral medium-range order due to a slight redistribution of constitutional elements during quasicrystallization. The formation of the nanoicosahedral phase in the Zr70Pd30 and Zr80Pt20 binary alloys appears to be attributed to the existence of the icosahedral medium-range order in the amorphous and/or liquid states.

Glass formation and crystallisation in rapidly solidified zirconium alloys

Zirconium-based alloys offer an unique opportunity for studying various aspects of metallic glass, namely glass forming ability, crystallisation modes and kinetics, diffusion mechanisms and formation of glass in bulk. Thermodynamic and kinetic rationale for glass formation have been summarised in binary and ternary metalloid free amorphous alloys rich in zirconium. A comparison has been made between the microstructures of the alloys obtained under different cooling rates in order to understand the process of solidification and the process of phase selection. The different types of nucleation processes and the growth mechanisms of crystals in the undercooled melts of Zr-based glass forming alloys have been investigated. Primary, eutectic as well as polymorphic crystallisation have been observed in the alloys of this class of materials. Crystal nucleation and growth kinetics during crystallisation has been examined.

Binary and ternary amorphous palladium alloys: Characterization, activity and selectivity in hydrogenation of dienes

Pd 25Zr 75, Pd 22Cu 10Zr 68, and Pd 72Cu 10Si 18 alloy ribbons prepared by the rapid quenching technique, and Pd 25Zr 75, Pd 25Cu 10Zr 65, Pd 80Si 20, and Pd 72Cu 10Si 18 alloy powders made by mechanical alloying proved to be amorphous by X-ray diffraction and differential scanning calorimetry. The powder samples after HF treatment have been found to exhibit high selectivity in the semihydrogenation of 1,3-cyclooctadiene: the pronounced drop in the hydrogen uptake after the complete consumption of the diene allows the selective synthesis of the corresponding monoene.

Highly metastable amorphous or near-amorphous ternary films (mictamict alloys)

Thin ternary films of the generic composition (early transition metal)–Si–(nitrogen or oxygen) can be synthesized that have an amorphous or near-amorphous structure and are highly resistant to crystallization upon thermal annealing. Common to all of them is the existence of two compounds that form a quasi-binary system. Some known properties of these films are reviewed. Their similarity with amorphous binary metallic alloys is emphasized. Many ternary systems should exist with which such amorphous films can be made. The name ‘mictamict’ is proposed to identify this general class of materials.

Formation of icosahedral quasicrystal by crystallization of Zr70(Ni, Cu, Pd)30 amorphous alloys

An icosahedral phase was found to be formed as a primary precipitation phase in the crystallization process of binary Zr70Pd30, ternary Zr70Ni30−xPdx, and Zr70Cu30−xPdx (x = 10 and 20 at.%) and quaternary Zr70Ni10Cu10Pd10 amorphous alloys. The maximum volume fraction of the icosahedral phase was nearly 100% for the 20% Pd alloys and the grain size tended to decrease in the range from 40 to 70 nm with increasing Pd content. No icosahedral phase was formed in the Zr–Ni–Cu alloys without Pd, and hence, the addition of Pd was concluded to be essential for the formation of the icosahedral phase in the Zr-based amorphous alloys. It also was noticed that the icosahedral phase was formed even in the binary Zr70Pd30 amorphous alloy. The icosahedral phase was in a metastable state and changes to equilibrium crystalline phases by annealing in the higher temperature range. The finding of the formation of the icosahedral phase in the binary alloy system allowed us to predict the future appearance of a number of icosahedral base alloys in other alloy systems.

Nanoquasicrystallization of binary Zr–Pd metallic glasses

The formation of an icosahedral phase during crystallization of Zr–Pd binary amorphous alloys is reported. The icosahedral phase forms in the nanocrystalline state with a grain size of about 10 nm as a metastable transient phase during the transformation from an amorphous to a crystalline state in Zr70Pd30 and Zr65Pd35 alloys. The amorphous phase coexists with the nanoquasicrystalline phase before complete crystallization to Zr2Pd occurs.

Temperature modifications of structural and magnetic characteristics of multicomponent amorphous cobalt-base alloys

In this study, on the basis of X-ray-structural data and the measurements of magnetic characteristics (the magnetic permeability, the maximum induction, and the coercive force), we have revealed correlations between modifications of structural and magnetic properties on various types of relaxation annealing. Moreover, by analyzing the correlation functions { A ( S ) and the radial-distribution function} and using values of structural parameters, we investigated the processes of the amorphous-state stabilization, the nucleation, and the growth of the crystalline phase for magnetically soft amorphous cobalt-base alloys obtained by the spinning of melts. We investigated the multicomponent amorphous alloys with the following compositions: Co 57 Ni 10 Fe 5 Si 11 B 17 , Co 67 Fe 3 Cr 3 Si 15 B 12 , and Co 68 Fe 4 Cr 4 Si 13 B 11 . All of these alloys have a virtually zero magnetostriction. The structure was analyzed with invoking the data of molecular-dynamic simulation for binary amorphous alloys Co 1 — x B x and Fe 1 — x B x [1]. For the alloys under consideration at room temperature, we observe a typical diffraction pattern with a pro

Characterization of amorphous Ni-Si binary alloy films by flash evaporation

We previously reported on an extremely small temperature coefficient of resistivity (TCR) of thin amorphous Ni-Si film resistors fabricated by new flash evaporating method, which have a wide range of resistivity.1 In the present paper, we describe the structural and chemical properties of these films for the purpose of clarifying the cause of resistive change of films resulting from heat treatment. X-ray diffraction patterns show that Ni-Si films with greater than 20 wt.% Si remains predominantly amorphous after heat treatment. Changes in composition and binding energy of the films resulting from heat treatment are measured by means of XPS. Electrical characteristics are also investigated as a function of Si concentration and temperature. The resistance variations resulting from heat treatment are found to originate from a structural change. The activation energy needed for this change is obtained by analyzing the extent of change during isothermal heating and found to vary from 1 eV to 2.5 eV with increasing Si content from 20 wt.% to 80 wt.%.

Short-Range Order of Amorphous (Zr65Al7.5Cu17.5Ni10)100—xFex Alloys

The short-range order of bulk glass forming (Zr 6.5 Al 7.5 Cu 17.5 Ni 10 ) 100-x Fe x alloys obtained by rapid quenching was investigated as a function of the iron content (x = 0 to 20). The structure of the bulk glass is found to be similar to binary amorphous Zr 65 M 35 alloys (M = transition metal). The observed changes in the interference function I(s) and the atomic pair correlation function g(r) are correlated to the altered zirconium content and are also similar to those in binary amorphous Zr-M alloys. Iron atoms are statistically distributed with the other transition metals within the amorphous phase.

Nanometer Scale Dynamics in Diffusion Limited Propagation of Interfaces in Amorphous Alloys

We quantify the nanometer scale avalanche dynamics of a propagating interface using time-resolved electron microscopy of binary amorphous Ge-Al alloys, which were heated and crystallized in a transmission electron microscope. Our observation of Ge-Al combines spatial resolution of nanometers with a time resolution of 0.04 sec. We find that the interface propagates by avalanches with a characteristic size of ${10}^{5}$ atoms. We develop a model that represents the amorphous phase as a random mixture and treats the diffusion process in the crystalline phase; we find that the model results agree with experiment.