Glassy Metal Alloys Research Articles

Structure of sputtered and melt-spun Ni-Zr glassy metals.

The Faber-Ziman total structure factors of a series of rf-sputtered and melt-spun ${\mathrm{Ni}}_{\mathit{x}}$${\mathrm{Zr}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$ glassy metal alloys have been measured for 0.25\ensuremath{\le}x\ensuremath{\le}0.86. The radial distribution functions and nearest-neighbor coordination numbers have been calculated. The measurements indicate that there is no discernible difference between the as-made structure of the sputtered and melt-spun materials. These data are reinforced by crystallization enthalpy measurements which also show no difference between the two preparation methods.

Structural and electrochemical effects induced in metallic glasses by mechanical deformation

Plastic deformation of glassy ribbons of Fe 80B 20 leads to the partial destruction of the short-range compositional order of the material. The electrochemical potential measured between two electrodes made from glass ribbons of composition Fe 40Ni 40B 20 shows a non-linear dependence of potential on the uniaxial deformation of one electrode. These effects explain the reduction of corrosion resistance of the glassy metallic alloys subjected to deformation.

XRD and raman identification of the zirconia modifications in copper/zirconia and palladium/zirconia catalysts prepared from amorphous precursors

Recently, highly active CO{sub 2} hydrogenation catalysts have been obtained from glassy metal alloy precursors, i.e., Cu{sub 70}Zr{sub 30} and Pd{sub 33}Zr{sub 67}. During in situ activation under CO{sub 2} hydrogenation conditions, the zirconium component of the alloy is oxidized. For Pd/zirconia, the support matrix is identified as stable, monoclinic ZrO{sub 2}. In copper/zirconia, on the other hand, a metastable zirconia modification is prevalent, corresponding to either tetragonal or cubic ZrO{sub 2}. As the XRD patterns of these metastable phases are quite similar, additional information is required to distinguish between the two modifications. Both infrared and Raman spectroscopy have been established as suitable techniques to differentiate between tetragonal and cubic zirconia, as the information from the vibrational spectra is complementary to the X-ray diffraction data. In addition to the identification of the zirconia modification, particular attention is drawn in the present report to the influence of copper in amorphous Cu/Zr-alloys on the crystallization behavior of the zirconia. For comparison, two copper/zirconia catalysts were prepared by co-precipitation, drying, and subsequent reduction in a hydrogen atmosphere. These catalysts, denoted as Cu 70 and Cu 50, contain 70 at.% copper and 50 at.% copper on zirconia, respectively. In addition, the catalyst Cu 50more » was calcined at 970 K for 2 h and then rapidly quenched to room temperature. The zirconia reference samples were precipitated, dried, and calcined, or else investigated without calcination.« less

Selective distribution and alignment of glassy metal reinforcement in complex moulded shapes

The currently employed methods of reinforcing epoxy resins with glass, carbon fibres or other elements are restricted to relatively simple shapes or to moulds with shapes that allow the flow of the two-phase mixture (the thermosetting or thermoplastic fluid and the solid reinforcement) through contracting or expanding cross-sections or against gravity. In such circumstances separation of the solid and liquid phases occurs, which tends to result in the absence of reinforcement in specific and sometimes critical regions of the moulded product. The object of this research was to alleviate this disadvantage of reinforced polymeric materials. A new method of moulding polymeric materials under such circumstances involves introducing a liquid polymeric material containing ferromagnetic glassy metal reinforcement elements into the mould, selectively applying at least one magnetic field to the mould to orient at least some of the ferromagnetic reinforcement in the liquid polymeric material and curing the resultant matrix. Glassy metals are a relatively new class of material formed when metallic alloys are cooled so rapidly that crystallization is bypassed and the alloy atoms form an amorphous structure [1]. This class of materials offers an unusual set of properties, having high mechanical strength and hardness, excellent soft magnetic properties, ductility, corrosion resistance and high electrical resistivity. A summary of useful mechanical properties and associated compositions is given in Table I. Such a variety of properties, the extent of which are dependent on the alloy composition, allows materials to be tailor-made to give a desired set of properties. The method of manufacture of glassy metals, melt-spinning, ideally lends itself to their use in epoxy reinforcement. The melt-spinning process ejects the molten alloy on to a spinning copper or steel wheel resulting in the TABLE I Mechanical properties of some glassy metal alloys Fe60Ni20- Fe54Crt6

Temperature dependence of electrocatalytic behaviour of some glassy transition metal alloys for cathodic hydrogen evolution in water electrolysis

A series of glassy transition metal alloys of various compositions, involving the elements Ni, Mo, V, Fe, Cr, Ti, together with B, have been investigated as electrocatalysts for the cathodic evolution of hydrogen. The polarization behaviour over a range of temperatures has been evaluated and exchange current-densities, Tafel slopes and apparent heats of activation have been determined. The Tafel slope behaviour as a function of temperature has been analysed to give the formal enthalpic ( α H) and entropic ( α S) components of the transfer coefficient or, for certain conditions, the barrier symmetry factor for charge transfer. Potential-relaxation experiments, following interruption of cathodic polarization currents, enable the pseudocapacitance, C φ , for H adsorption to be evaluated as a function of overpotential, η. Integration of the C φ vs η relation for one of the NiMo based alloys suggests that cathodic H 2 evolution takes place through proton discharge on to a surface substantially covered by H, a factor that is related to the tendency for some of these glassy metals to form hydride phases during H 2 generation.

Hydride formation at Ni-containing glassy-metal electrodes during the H 2 evolution reaction in alkaline solutions

A group of Ni-containing glassy metal alloys that are of interest as electrocatalysts for cathodic hydrogen production in water electrolysis have been examined with regard to the role of hydride formation and the participation of sorbed H during cathodic H 2 evolution in alkaline solutions. Hydride formation is important as it may determine, in part, the electrocatalytic properties of the alloys at their surfaces, for cathodic H 2 evolution. Characteristic time-dependences of currents observed near, but negative to the H 2 reversible potential in response to a stepwise change of potential, together with potential-relaxation measurements on open-circuit following current interruption, lead to the conclusion that a three-dimensional hydride is formed in the near-surface region of the metals during the H 2 evolution process. Complementary cyclic-voltammetry experiments show that hydrogen deposition-absorption, or H oxidation processes, can be distinguished from possible spontaneous oxidation of the glassy metals, over somewhat overlapping potential regions.

Electronic properties of glassy metallic alloys

For computer-generated models of glassy Fe 1−xB x ( x = 0.15–0.50) and Cu 1−yZr y systems ( y = 0.35–0.65) with about 2000 atoms, numerical calculations of the electronic densities of states and the electronic transport properties were performed using a continued-fraction algorithm. For the densities of states of Fe 1−xB x, two different termination procedures which yield almost the same results are compared. The results for the densities of states and the resistivities for both systems agree with experimental data.

The need for microstructural control in coatings exposed to severe environments

Very fine grained or amorphous microstructures often improve the performance of coatings exposed to severe environments. Several examples are discussed to illustrate the desirability of controlling processing conditions to achieve microstructural control.In some cases, better environmental resistance is obtained from amorphous materials that exist in a metastable state of equilibrium. Since metastable phases are typically in a higher energy state, this observation is not intuitively obvious. For example, metastable glassy metal alloys exhibit significantly improved aqueous corrosion resistance. Here, the absence of grain boundaries appears to be the predominant factor. Very fine grained and amorphous optical coatings demonstrate improved laser damage resistance and better stability in the presence of humidity. It is suggested that compositional homogeneity is a principal factor in this performance.At high temperatures, the formation of protective glassy SiO2 provides better oxidation protection than the stable, higher melting point refractories do because the concentration of lattice defects in the crystalline oxides allows unacceptably high oxygen diffusion rates. Amorphous silica performs better until higher temperatures lower the viscosity and offset its advantage.Many of the coating microstructures used for illustration purposes were obtained by sputtering. However, it is the resultant microstructure that is of importance and not the process by which it was achieved. Process parameters can frequently be used to control the microstructure and thereby provide a means of improving coating performance under exposure to severe environments.

Glassy metal alloys with perminvar characteristics

A number of glassy metal alloys with near-zero magnetostriction have been found to exhibit perminvarlike properties of relatively constant permeability at low magnetic fields and constricted B-H loops. A wide variety of perminvar properties can be obtained by varying heat-treatment conditions and the compositions of the materials. The low field permeability and dc coercivity of the glassy alloy perminvars can range between about 600 and 90 000 and between about 0.2 and 12 A/m, respectively. The magnetic shock problem associated with the crystalline perminvars is absent in these materials.

Melting of Ni40Pd40P20 glass

Upon reheating, most glassy metal alloys crystallize at a temperature not far removed from the glass temperature Tg and far below the liquidus temperature Tl. We have reported that the alloy Ni40Pd40P20, which exhibits a scaled glass temperature ∼0.68, has been melt quenched, under a flux of dehydrated B2O3, to glass at rates as low as 1°/s. Here we report experiments in which some specimens of this alloy, when similarly fluxed during reheating, have been reheated to temperatures within 50° of Tl and 280° above Tg at rates ∼2.5°/s, and then cooled again to Tg, without crystallization. From this behavior we infer that the steady frequency of homogeneous nucleation of crystals in the alloy is <10−1 cm−3 s−1.

Low-temperature enhancement of the thermopower of La-Al, Ca-Al and Ca-Al-Ga glassy metal alloys

Enhancements of the low-temperature thermopower of several La-based and Ca-based glassy alloys are compared with the predictions for the electron-phonon enhancement. The agreement is reasonably good for the La-based alloys, but unexpected structure is observed for the Ca-based alloys. The measurements suggest that the low-frequency alpha 2( omega )F( omega ) is proportional to omega beta with beta >1 for these alloys.

Catalytic Properties of Glassy and Crystalline Transition Metal Alloys Produced by RSP

ABSTRACTThe catalytic activity and selectivity of Pd80Si20, Pd35Zr65Ni30Zr70, Fe40Ni40B20, Fe85B15and Cu50Zr50alloy ribbons in their amorphous and crystalline states were studied in the hydrogenation of 1—hexene and phenylethyne, dehydrogenation of methylcyclohexane and dehydrocyclization of n—heptane. Pd80Si20was found to be the most active of the alloy catalysts studied. Most alloys were more active amorphous than in the crystalline state; however, the catalytic selectivities of the amorphous and crystalline states of each alloy were identical.

Homogeneous flow and anelastic/plastic deformation of metallic glasses

Nonelastic deformation of glassy metallic alloys is analysed. Both the anelastic and viscoplastic aspect of deformation, the relation between strain rate and stress,'and the effect of structural relaxation are considered. A model of homogeneous deformation of metallic glasses near T g which takes into account all the experimental features is proposed. According to this model, plastic deformation is principally dependent on the recovery processes (implying atomic diffusion) which occur after the shear microdomains are formed. By introducing a distribution of times, which is characteristic of the thermo-mechanical nucleation of the shear microdomains, expressions, which quantitatively describe the experimental data, are obtained.

On the magnitude of the electrical resistivity of liquid and glassy transition metal alloys

We discuss the magnitude and the concentration dependence of the electrical resistivity of liquid and glassy transition metal alloys. We present the measured resistivities of Cu-Zr glasses (25–75 at % Zr) and analyze the results in terms of a simple two-band model. On the basis of a semi-empirical fit of the experimental data, we conclude that at the Zr rich end, the contribution of d-electrons to the total conductivity should not be neglected.

EXAFS of glassy metallic alloys: Amorphous and crystalline MoNi

The Ni and Mo K-edge extended X-ray absorption fine structure (EXAFS) spectra of MoNi alloy in the amorphous and crystalline δ-phase have been measured in the transmission mode. The EXAFS spectrum of a Mo foil has also been measured for comparison. The EXAFS data were analyzed using both symmetrical (Gaussian) and asymmetrical (liquid-metal type) pair distribution functions. A newly developed fine adjustment technique based on model (FABM) was applied to the best fit results based on theoretical backscattering amplitude and phase functions. The following results were obtained. (1) There exist differences in distances between the crystalline (r c) and the amorphous ( r a) alloys, which follow the general trend: Ni Ni (r c − r a ≈ 0 A ̊ ⩽ Mo Ni(0.03 A ̊ ) < Ni Mo(0.10 A ̊ ) ⪡ Mo Mo(0.2 A ̊ ) . (2) The distances between unlike atoms obtained from the Ni K-edge spectra (NiMo) and from the Mo K-edge spectra (MoNi) are different for both amorphous and crystalline states. The differences, in terms of (NiMo)−(MoNi), amount to 0.06 Å in the amorphous and 0.13 Å in the crystalline states. (3) The coordination numbers obtained by EXAFS for the metallic alloys are abnormally low ( N = 1–4) in sharp contrast to those ( N = 5–8) expected from crystallography. These features are interpreted in terms of large local atomic disorder, asymmetry in the pair distribution functions, and phase cancellation between the nickel and the molybdenum waves (the backscattering phases are off by π radians). Fits with the asymmetric pair distribution function are, however, of similar or somewhat poorer quality than those with symmetric ones and follow the same trends. Parameter correlation characteristics reveal distinct differences among metal foils, crystalline metal alloys, and amorphous metal alloys. These differences can be attributed to the different pair distribution functions, indicating that neither the crystalline metal foils nor the crystalline metal alloy can be used as model for the amorphous metal alloy. Our results indicate that in the MoNi alloy the nearest neighbor interactions are to some extent preserved while the higher shell coordinations are increasingly diminished in going from the crystalline phase to amorphous phase.

Electrical conduction in some glassy metal alloys in the presence of magnetic fields and tensile stresses

The relative change in the electrical resistivity of glassy Fe80B20, Fe78Mo2B20, Fe40Ni40P14B6, and Fe32Ni36Cr14P12B6 have been investigated at 295 K as a function of longitudinal and transverse magnetic fields and tensile stresses. The low field magnetoresistivity of Fe32Ni36Cr14P12B6, which is nonferromagnetic at 295 K, is negligible. In principle, our data in the above ferromagnetic glasses are consistent with the expectations from the domain theory for positive magnetostrictive materials. However, the above glasses do not obey the equivalence principle between the magnetic field and the stress. It has been found that the ferromagnetic anisotropy of the electrical resistivity is approximately stress-independent.

Uses of glassy metal alloys expanding

Metal alloys, when cooled rapidly enough, do not form small crystals of discrete metals as they do when they cool more slowly. Instead, an amorphous solid forms in which the atoms are distributed much more randomly. This glassy metallic material, which has fascinated metallurgists for decades, now is proving equally fascinating to applications engineers. These glassy metals have properties that give them wide commercial applications. Their unusual magnetic properties, for example, are being exploited in new types of electrical devices that may have substantially lower energy requirements than conventional devices. And their resistance to corrosion makes possible a low-chromium stainless steel-like coating that has corrosion properties much like pure titanium. One of the leading companies in the field is Allied Corp., which has developed a product it calls Metglas. Allied is promoting Metglas, which has been available commercially since 1978, primarily for use in electrical devices such as motors and trans...

Spin-Glass-Ferromagnetic "Phase" Transitions in Amorphous Soft Magnetic Systems

In this paper, the general features of the magnetic phase diagrams, determined experimentally by a.c.-susceptibility and other techniques, for glassy metallic alloys of the type (AxB1-x)75P16B6Al3 (where A, B are transition elements Fe, Co, Ni, Mn or Cr) with mixed exchange interactions are reviewed. Evidence for a second-order nature of the transitions across the para-, ferro-, and spin-glass "phase"-boundaries using scaling techniques are discussed. Manifestations of the transitions across the para to ferro followed by the ferro- to spin-glass phase boundaries at lower temperatures as observed in various experimental techniques are also briefly presented.

Varying d-band splitting in glassy transition metal alloys

The valence bands and core levels of a wide variety of metallic glasses (FeZr, CoZr, NiZr, CuZr, PdZr, PtZr, CuTi, NiNb and NiTa) have been studied by UPS and XPS. The valence band spectra are characterized by varying d-band splitting and binding energy shift. Within a given series the d-band splitting is increased with increasing number of groups between the two constituents in the periodic table. The correlation between this electronic structure and glass forming ability and alloy heats of formation is discussed.

Near surface yield enhancement in narrow acceptance 180° elastic scattering for He ions in non-crystalline and poly-crystalline solids

Observations of an unusual near surface ( 0 ⩽ x< 700 A ̊ ) yield enhancement in the energy distribution of elastically scattered He ions from amorphous and polycrystalline materials is reported. The integrated excess yield for small ( θ 1 2 =0.2° ) versus large ( θ 1 2 =4.5° ) acceptance angle at 180° scattering is typically 20% for He energies in the range 0.2 ⩽ E⩽2.5 MeV. Maximum peak to normal yield ratios have been observed as high as 60–70%. Materials in which the effect has been observed include amorphous germanium, the glassy metal alloy Nb 40Ni 60, fine grain polycrystalline Au, Pt, Mo, and Cu and also in single crystals of Si and Au continuously rotated during data collection to simulate a random lattice. The excess yields are largest for materials of atomic number above Z=40 and decreases rapidly for elements below this value. The angular width and depth dependence of this effect suggest that it is sensitive to multiple scattering and also implies that the particle, upon scattering, must retrace its inward path within a cone of ≲0.2° from depths comparable to or less than a few hundred Å.