Amorphous Metallic Alloys Research Articles

Studying the applicability of amorphous metal alloys as interface material for power electronics packaging

All-atom Molecular Dynamics simulations were used to study the coefficient of thermal expansion (CTE) in Cu/Zr amorphous alloys with various compositions. We explored the possibility of using these alloys as bonding interface material between ceramics chips and copper leads in power electronics and microelectronic packaging applications with an objective of reducing CTE mismatch at the bonding interface. It was expected that with the appropriate design of reduced CTE mismatch at the interface, the Cu/Zr bonding layer could withstand larger thermal loads and significantly extend device life compared to the devices that currently implement directly bonded copper (DBC) approach. The non-monotonic increase of material CTE with copper content in the alloy was analyzed and explained using new tessellation algorithm that is focused on the configuration of close contacts between the neighboring atoms. The modeling using Turner equation shows that the “leveling” of CTE dependence in the mid-composition range is due to the contribution from non-tetrahedral polyhedra and would be expected for any binary glass system. Contrary to that, the “dip” at Cu-rich compositions is caused by the nature of the metallic bonding in the alloy, and is specific to Cu-Zr glass.

Radiation Effects in Amorphous Metallic Alloys as Revealed by Mössbauer Spectrometry: Part I. Neutron Irradiation

Iron-based amorphous metallic alloys (AMAs) of several compositions were exposed to neutron irradiation with fluences of up to 1019 n/cm2. These materials exhibit excellent magnetic properties which predetermine them for use in electronic devices operated also in radiation-exposed environments. Response of the studied AMAs to neutron irradiation is followed by Mössbauer spectrometry which probes the local microstructure. Neutron irradiation leads to rearrangement of constituent atoms, their clustering, and formation of stress centers. The observed modifications of topological short-range order result in changes of spectral parameters including average hyperfine magnetic field, ⟨B⟩, standard deviation of the distribution of hyperfine fields, and position of the net magnetic moment. After irradiation, especially differences in ⟨B⟩-values develop in two opposite directions. This apparent controversy can be explained by formation of specific atomic pairs with different exchange interactions, which depend on the composition of the samples. Part II of this paper will be devoted to radiation effects caused in Fe-based AMAs by ion irradiation.

Corrosion Resistance of Co77Si11B12 Amorphous Metal Alloys for the Electrodes of Hydrogen Release from Alkaline Solutions

Corrosion Resistance of Co77Si11B12 Amorphous Metal Alloys for the Electrodes of Hydrogen Release from Alkaline Solutions

Control of magnetic properties in ferrimagnetic GdFe and TbFe thin films by He+ and Ne+ irradiation

The impact of kiloelectronvolt ${\mathrm{He}}^{+}$ and kiloelectronvolt ${\mathrm{Ne}}^{+}$ ion irradiation on the magnetic properties of rare earth-3$d$ transition metal amorphous alloys was investigated. The studies were performed for 20-nm-thick ${\mathrm{Gd}}_{x}{\mathrm{Fe}}_{100\ensuremath{-}x}$ and ${\mathrm{Tb}}_{x}{\mathrm{Fe}}_{100\ensuremath{-}x}$ films with perpendicular magnetic anisotropy, irradiated with doses ranging from $5\ifmmode\times\else\texttimes\fi{}{10}^{13}$ to $5\ifmmode\times\else\texttimes\fi{}{10}^{15}\phantom{\rule{0.16em}{0ex}}\mathrm{ions}\phantom{\rule{0.16em}{0ex}}\mathrm{per}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}$. We demonstrate that this approach can be used to engineer magnetic properties such as magnetization, magnetic anisotropy, and compensation temperature in both alloys and to control the spin-flop reorientation transition in GdFe. We find that fine-tuning of the compensation point is possible without losing perpendicular magnetic anisotropy by appropriate selection of ion energy and irradiation dose. The experiments were supported by atomistic simulations revealing that the observed changes can be attributed to selective oxidation of rare earth atoms. Oxidation of 1% of atoms in the lattice gives reasonable agreement to the experimental results for low and medium ion doses.

Direct observation of atomic-level fractal structure in a metallic glass membrane

Determination and conceptualization of atomic structures of metallic glasses or amorphous alloys remain a grand challenge. Structural models proposed for bulk metallic glasses are still controversial owing to experimental difficulties in directly imaging the atom positions in three-dimensional structures. With the advanced atomic-resolution imaging, here we directly observed the atomic arrangements in atomically thin metallic glassy membranes obtained by vapor deposition. The atomic packing in the amorphous membrane is shown to have a fractal characteristic, with the fractal dimension depending on the atomic density. Locally, the atomic configuration for the metallic glass membrane is composed of many types of polygons with the bonding angles concentrated on 45°–55°. The fractal atomic structure is consistent with the analysis by the percolation theory, and may account for the enhanced relaxation dynamics and the easiness of glass transition as reported for the thin metallic glassy films or glassy surface.

X-ray Diffraction Computed Nanotomography Applied to Solve the Structure of Hierarchically Phase-Separated Metallic Glass.

The structure of matter at the nanoscale, in particular that of amorphous metallic alloys, is of vital importance for functionalization. With the availability of synchrotron radiation, it is now possible to visualize the internal features of metallic samples without physically destroying them. Methods based on computed tomography have recently been employed to explore the local features. Tomographic reconstruction, while it is relatively uncomplicated for crystalline materials, may generate undesired artifacts when applied to featureless amorphous or nanostructured metallic alloys. In this study we show that X-ray diffraction computed nanotomography can provide accurate details of the internal structure of a metallic glass. We demonstrate the power of the method by applying it to a hierarchically phase-separated amorphous sample with a small volume fraction of crystalline inclusions, focusing the X-ray beam to 500 nm and ensuring a sub-micrometer 2D resolution via the number of scans.

Nanostructure and compositional segregation of soft magnetic FeNi\u2010based nanocomposites with multiple nanocrystalline phases

Soft magnetic metal amorphous nanocomposite alloys are produced through rapid solidification and thermal annealing yielding nanocrystals embedded within an amorphous precursor. Similar free energies in Co‐rich and FeNi‐based alloy systems result in multiple nanocrystalline phases being formed during devitrification. Studies of multi‐phase crystallization processes have been reported for Co‐rich alloys but relatively few have investigated FeNi‐based systems. A detailed characterization of compositional partitioning and microstructure of an optimally annealed FeNi‐based MANC (Fe70Ni30)80Nb4Si2B14 alloy is presented through complementary high‐resolution transmission electron microscopy (HRTEM) and atom probe tomography (APT). HRTEM demonstrates orientation relationships between FCC and BCC nanocrystals, suggesting heterogeneous nucleation of nanocrystals in the amorphous matrix or a cooperative mechanism of nucleation between BCC and FCC nanocrystallites. APT results show evidence for (i) the segregation of Fe and Ni between nanocrystals of different phases, (ii) B partitioning to the amorphous phase, and (iii) an Nb‐enriched shell surrounding nanocrystals.

Features of modification of amorphous metallic alloys by oligomeric coatings

By potentiometric method it was investigated the dissolution in 0.5 M NaCl aqueous solution of the initial amorphous metallic alloys Fe 78,5 Ni 1,0 Mo 0,5 Si 6,0 B 14,0 , Со 75.5 Fe 4.5 Si 6.0 B 14.0 , and with the applied oligoperoxide layers. Preliminary chemical cleaning by HF of the surfaces of original amorphous alloy activates their corrosion, and subsequent aging in a solution of KMnO 4 helps to restore the oxide protective layers. In an aggressive environment of sodium chloride oxide films are dissolved and corrosion of the amorphous alloyʼs surface is presented. It is importante to create additional protection of the alloys surface by applying oligomeric layers. After the formation of an oligoperoxide film on such a surface, the value of the stationary potential does not change upon contact with an aggressive medium, which is associated with the creation of additional resistance to the transfer of charged particles. According to electrochemical parameters, the stability of oligoperoxide films was evaluated: vinyl acetate, 2-tert-butylperoxy-2-methyl-5-hexen-3-yne and maleic anhydride (OP-1), vinyl acetate, 3-tert-butylperoxy-3-phenylbutylmethacrylate and maleic anhydride (OP-2) on the investigated amorphous alloys. It was shown that more stable films are formed on the external side of the tape of amorphous alloy, which contains a larger proportion of the crystalline phase. It was established that the stability of the obtained films significantly depends on the concentration of the film-forming solution. With increasing concentration of the oligoperoxide solution, it is possible to change the conformation of the adsorbed macromolecules and rearrange the adsorption layer, which often reduces the density of the film. The densest films are formed on the surface of alloys based on iron with 0,5 % OP-1 aqueous-ammonia solutions of oligoperoxides, and based on cobalt - with 0,1 % solutions OP-1 and OP-2. Keywords: amorphous metallic alloys, oligomeric coatings, potentiometry, corrosion resistance.

Autocatality effect of AlCl3 applications on the oxidation process of amorphous Al87Ni8Y5 alloy in 0.5 M aqueous NaCl solution

Investigation of corrosion resistance of amorphous metal alloy ( AMA ) from aluminum is carried out in 0.5 M aqueous solutions of NaCl. Cl- ions penetrate the oxide layer through pores or defects and can colloidally disperse the oxide film and increase its permeability . The Al 87 Ni 8 Y 5 were obtained by melt spinning technique in helium atmosphere onto a copper wheel with a circumferential speed of about 30 m/sec (cooling rate = 10 6 К/sec). The method of voltammetry in the potential-dynamic mode showed that the introduction of AlCl 3 (7.4·10 -3 mol/l) in the system of origin reduces the first maximum, which is responsible for the adsorption of Н + on the AMА electrode. A potentiostatic ivestigates of the behavior of Al 87 Ni 8 Y 5 in 0.5 M aqueous NaCl solution with additional elements AlCl 3 indicates the autocatalytic properties of a low concentration of AlCl 3 (2·10 -7 mol/l), which contributes to the dissolution of the surface. The kinetics of establishing the stationary potential in 0.5 M aqueous NaCl solution and with AlCl 3 applications were chronopotentiometrically investigated. The presence of AlCl 3 ions in the background electrolyte during chronopotentiometry of AMA Al 87 Ni 8 Y 5 in 0.5 M aqueous sodium chloride solution reduces the position of the potential dependence. To independently confirm the influence of Al 3+ and Cl - ions on the processes of formation of protective layers on the surface of Al 87 Ni 8 Y 5 in 0.5 M aqueous NaCl solution using a electron microscope. Micrographs of the alloy surface were taken after VA removal in NaCl background solution 1M application of AlCl 3 , the surface of the alloy in NaCl solution is covered with a thin layer of oxides and hydroxides of aluminum, and due to the sweep potentials in the range of -1000 ÷ +300 mV in the presence of AlCl 3 a multilayer coating is formed. Keywords: amorphous metallic alloys, passivation layers, corrosion resistance.

A theory for coupled lithium insertion and viscoplastic flow in amorphous anode materials for Li-ion batteries

Amorphous lithium metal alloys (LixM, with M=Si, Ge, Sn, …) are attractive anode materials for lithium-ion batteries owing to their high energy-storage capacity and safety characteristics. However, repeated insertion of lithium often leads to chemo-mechanical degradation of the alloy, which can severely reduce the battery capacity and cycle life. Better understanding of the chemo-mechanical response of lithium alloys is needed to guide the design of damage-resistant anode microstructures. In this work, we propose a constitutive theory that couples large, viscoplastic deformations to the insertion and extraction of lithium in amorphous electrode materials. The theory relies on the concept of Shear Transformation Zone as carrier of plastic flow in the amorphous material, and accounts for microstructural evolution via an internal “free volume” variable. The model is used to gain insight into several features of the plasticity of amorphous alloys during lithiation, including rate-dependency, pressure-dependency, and structural evolution. Model predictions are also compared to experimental data for amorphous silicon.

Composition-driven transition from amorphous to crystalline films enables bottom-up design of functional surfaces

Composition-driven transition to the crystalline state is characteristic of amorphous metal alloys and is widely observed in thin film. However, the transition zone (compositional range between single-phase amorphous and crystalline films) remains unexplored. Here, we demonstrate that this transition offers an excellent scenario for the fabrication of hybrid crystalline-amorphous architectures. The peculiar morphology of these nano(micro)-structured films provides a simple bottom-up route, applicable to a broad range of alloys, for obtaining adjustable multifunctional surfaces. In particular, we prove the feasibility of this approach as a one-step process for a precise control of specular and diffuse reflectance over the visible spectrum. Further, the growth kinetics of the formed two-phase nanostructures is demonstrated equivalent to a 2-dimensional amorphous-to-crystalline phase transformation. Using Zr-W alloys as a model system, fundamental parameters of the growth process and the corresponding metastable thickness-composition phase diagram are extracted. It evidences that the two-phase nanostructures, despite occurring in a wide range of compositions, can be easily hidden experimentally by growth kinetics and nucleation delay. These results open a new avenue on the surface morphology and related functional properties control in thin films.

Calorimetric Effects in the Structural and Phase Transitions of Metals and Alloys

Differential scanning calorimetry belongs to a group of rather unique study methods, which makes it possible to investigate in situ the regularities of structural and phase transitions in metallic alloys within a broad range of temperatures (from –100 to 1600°C) at a sufficiently high precision of registering the heat effects of phase transitions. Our paper reviews the results of DSC studies for the alloys based on metals with polymorphism, the thermoelastic martensitic transitions, the decomposition and formation of solid solutions, and the crystallization of amorphous metallic metal-metal alloys. This review puts particular emphasis on considering phase transitions in hydrogen-containing alloys, both crystalline and amorphous.

Effect of simultaneous improvement of plasticity and microhardness of an amorphous-nanocrystalline material based on Co, as a result of laser processing of nanosecond duration

Experimental investigations of the properties of nanostructured materials are of large practical significance. Physical and chemical properties of nanocrystalline and amorphous-nanocrystalline alloys are currently being actively researched. Yet, the practical use of such materials is complicated by the lack of an optimal set of physical and mechanical properties. Classical processing methods are not effective enough. Laser processing is a promising method for forming specified mechanical properties. Amorphous-nanostructured materials, as a result of local and ultrafast exposure to high temperatures and pressure, retain their structure almost unchanged. At the same time, plasticity and microhardness can remain at a high level, and in some cases even increase during processing. The relevance of the presented work lies in the study of the regularities of the simultaneous increase in plasticity and microhardness of an amorphous Co-based nanocrystalline metal alloy, due to its processing with nanosecond laser pulses. The relevance of the presented work lies in the study of the patterns of the simultaneous increase in plasticity and microhardness of an amorphous Co-based nanocrystalline metal alloy due to its processing with nanosecond laser pulses.

High-intensity pulsed ion beam treatment of amorphous iron-based metal alloy

The results of intense pulsed ion beam (IPIB) treatment of the soft magnetic amorphous alloy of a FINEMET-type are presented. Foil produced from the alloy was irradiated with short (about 100 ns) pulses of carbon ions and protons with energy of up to 300 keV and an energy density of up to 7 J/cm2. X-ray diffraction, Mössbauer spectroscopy and magnetic measurements were used to investigate structural and magnetic properties of irradiated foils. It is shown that the foil remains intact after the treatment, and the crystal structure still amorphous. Spontaneous magnetization vector is found to lie almost along perpendicular to the foil plane after irradiation, whereas for the initial amorphous foil it belongs to the plane. The magnetic properties of the foil undergo changes: the coercive force decreases, the saturation induction increases slightly, and the magnetization curve has shallower slope.

A method to quantify crystallinity in amorphous metal alloys: A differential scanning calorimetry study

We developed and describe a differential scanning calorimetry method for calculating the initial crystallinity, change of crystallinity and crystallinity percentage of amorphous metal alloys as a function of temperature. Using thermodynamic enthalpies of amorphous, crystalline and partially devitrified specimens, our methodology is capable of determining crystallinity percentages as low as a few percent. Moreover, the linear relationship between the set (pre-determined) and calculated crystallinities of experimental samples indicates that there is no need to prepare calibration samples before measuring the crystallinity percentage of target samples. This technique also eliminates the need for expensive in situ accessories, such as those required in electron microscopy. Thus, the technique is highly relevant as a primary technique for characterization of devitrification behavior in amorphous materials.

Metallic amorphous alloy for long-term stable electrodes in organic sensors and photovoltaics

Amorphous metallic alloy, i.e. metallic glass (MG), is a metal without long-range ordered atomic arrangements. The unique structural property of MGs contributes to the superior mechanical and chemical properties to that of conventional metals. In this research, the unique characteristics of MG is considered for fabrication of long-term stable thin film strain sensors and the electrode for organic solar cells. MG thin film with zirconium (Zr) based composition exhibited encouraging results on strain sensing, showing high mechanical stability with reversible resistive response under the applied strain by bending. Furthermore, MG thin films with aluminum (Al) based composition exhibited high chemical stability, which contributed to the organic solar cell's stable operation without significant degradation in performance. Thus, the results suggest that MG is a promising material to realize long-term sustainable organic photovoltaic device. • Newly designed metallic glasses (MGs) of zirconium (Zr) and aluminum (Al) were investigated for organic thin film devices. • Zr-based MG exhibited improved stable resistive response with respect to exerted strains. • Al-based MG was sputtered onto MoO x layer for long-term stable photovoltaic operations. • MG electrodes’ superior mechanical and chemical stability contribute to enhanced reliability of the flexible devices.

Corrosion resistance of W and Ta based amorphous coatings in a geothermal steam environment – A combinatorial study

Amorphous films of WSi and TaSi have been deposited by DC magnetron sputtering in order to determine their corrosion resistance in geothermal steam. A combinatorial approach is employed whereby samples with composition gradients are deposited and analysed for amorphicity, temperature stability and corrosion resistance. WSi and TaSi form amorphous metal alloys over the composition range 4–60 at.% W and 12–80 at.% Ta, respectively. The amorphous structure of both alloys is stable up to temperatures well exceeding those encountered in a geothermal power generation environment. W-based amorphous alloys undergo severe corrosion when subjected to 30 days in geothermal steam whereas Ta-based amorphous alloys are not significantly affected by the same conditions. This shows that combinatorial methods can be employed to screen efficiently corrosion resistant materials and that Ta-based amorphous alloys are promising for applications in geothermal power generation.

Magnetically induced synthesis of mesoporous amorphous CoB nanochains for efficient selective hydrogenation of cinnamaldehyde to cinnamyl alcohol

Amorphous metal-boron alloys have attracted extensive interest in catalytic reactions because a large number of randomly oriented bonds constitute a glass-like structure with abundant defects and unsaturated surface atoms which are catalytically active. However, the synthesis of non-precious amorphous metal-boron with a multilevel structure remains a challenging task. Here, ultra-long mesoporous cobalt-boron (CoB) amorphous alloy nanochains are firstly synthesized by using the soft-templating approach with the assistance of a magnetic field. Owing to the high surface area and the unique behavior of Co within the Co-B alloy, mesoporous CoB nanochains show superior activity and selectivity in liquid-phase cinnamaldehyde (CMA) hydrogenation in cinnamyl alcohol (CMO). This work opens an avenue for the exploration of mesoporous amorphous metal alloys towards liquid-phase selective hydrogenation reaction.

Thermal Stability of Fe82Nb2B14REM2 Amorphous Alloys

We analyze the thermal stability and kinetic parameters of crystallization of Fe82Nb2B14REM2 (REM = Y, Gd, Tb, or Dy) amorphous metallic alloys by the method of differential scanning calorimetry. It is shown that the alloys based on iron crystallize in two stages. We compute the activation energy of both stages of crystallization of amorphous alloys according to the Kissinger, Ozawa, and Augis–Bennett models. The procedure of doping of the Fe84Nb2B14 alloy with rare-earth metals leads to an increase in temperature, in the activation energy of crystallization, and in the frequency factor. The decrease in the crystallization rate constant of alloys caused by doping with rare-earth metals reveals their resistance to temperature treatment.

Influence of HPT Deformation on the Structure and Properties of Amorphous Alloys

Recent studies showed that structural changes in amorphous alloys under high pressure torsion (HPT) are determined by their chemical composition and processing regimes. For example, HPT treatment of some amorphous alloys leads to their nanocrystallization; in other alloys, nanocrystallization was not observed, but structural transformations of the amorphous phase were revealed. HPT processing resulted in its modification by introducing interfaces due to the formation of shear bands. In this case, the alloys after HPT processing remained amorphous, but a cluster-type structure was formed. The origin of the observed changes in the structure and properties of amorphous alloys is associated with the chemical separation and evolution of free volume in the amorphous phase due to the formation of a high density of interfaces as a result of HPT processing. Amorphous metal alloys with a nanocluster structure and nanoscale inhomogeneities, representatives of which are nanoglasses, significantly differ in their physical and mechanical properties from conventional amorphous materials. The results presented in this review show that the severe plastic deformation (SPD) processing can be one of the efficient ways for producing a nanocluster structure and improving the properties of amorphous alloys.