Homogeneous Amorphous Structure Research Articles

A Lightweight AlTiVNb High-Entropy Alloy Film with High Strength-Ductility Synergy and Corrosion Resistance.

The simultaneous improvement of mechanical and corrosion resistance is of great significance for engineering applications. In this work, a novel lightweight amorphous structure AlTiVNb high-entropy alloy (HEA) film was fabricated by magnetron sputtering. The compression test of the AlTiVNb HEA film nanopillar exhibits a high compressive strength of up to 3.6 GPa and deformability approaching 58%. The high strength is affected by the disordered state, the nanostructure, and the lattice distortion effect, while the high ductility comes from the ductile shear band and the island structure. In addition, the AlTiVNb HEA film shows a current density of 4.90 × 10-8 A/cm2 and a potential of -0.234 V in the 3.5% NaCl solution, comparable to that of the 316L stainless steel. The chemical disorder state, cocktail effect, and homogeneous amorphous structure contribute to excellent corrosion resistance. This finding offers new insights into high-performance HEA films with robust mechanical and anticorrosion performances for microelectronic devices and mechanical metamaterials.

Crystallization behavior and corrosion resistance of Al86Ni10Zr4 amorphous alloy under different annealing treatment conditions

Thermal stability, structural evolution and corrosion resistance of melt spun Al86Ni10Zr4 amorphous alloy under different annealing treatment conditions were investigated via differential scanning calorimetry (DSC), X-ray diffractometry (XRD), transmission electron microscopy (TEM) and electrochemical tests. It is shown that the Al86Ni10Zr4 amorphous alloy has a large crystallization zone width and can remain amorphous for a long time at room temperature without crystallization and has high thermal stability. Structural characterization and properties analysis showed that the nano-sized α-Al phase precipitated on the amorphous matrix after annealing at 523 K improved the corrosion resistance of the ribbon, which is due to the fact that the corrosion resistance depends not only on the homogeneous amorphous structure but also on the content of oxides in the surface passivation film.

Revealing the effects of melt temperature on structure and magnetic properties in Fe–Si–B–C alloy

The effects of melt temperature in range of 1150–1400 °C on amorphous structure, magnetic properties and magnetic structures of Fe–Si–B–C amorphous ribbons were systematically investigated. The results of high-resolution transmission electron microscopy confirm that there exist a number of metastable nano-scales clusters in the quenched ribbons spinning at low melt temperature (1150 and 1300 °C). The measurement of flash differential scanning calorimetry finds that the thermal stability of the quenched ribbons notably increases with melt temperature elevating, also implying that higher melt temperature favors the higher degree of amorphization for the alloy. During the crystallization annealing process, the metastable Fe23(B, C)6 phase is preferentially precipitated at high melt temperature (1400 °C). The magnetic structure analyzed by magnetic force microscope reveals that a wide and uniform distribution of domain can be obtained in the alloy spun at high melt temperature (1400 °C), and that the domain size (width and length-breadth ratio of domain) is well correlated with coercivity and effective permeability. These current results provide important insights into the correlation between melt temperature and magnetic structure of Fe-based amorphous ribbons and are helpful to guide the production of Fe-based amorphous ribbons with homogeneous and stable amorphous structure from the technical level.

Study of micro indentation assisted deformation on HPT processed Zr62Cu22Al10Fe5Dy1 bulk metallic glass

In the present work, investigation on high pressure torsion (HPT) and accumulative HPT (ACC HPT) processed Zr62Cu22Al10Fe5Dy1 bulk metallic glass (BMG) is performed. BMG plate was cut into four pieces (disc) for HPT and ACC HPT processing. BMG specimens obtained after n=2, 10 and 11 revolutions of the HPT and ACC HPT are termed as BMG 2, BMG 10 and BMG 11, respectively. Alloys are found to retain the glassy phase before and after HPT process. Homogeneous amorphous structure of BMG initial is obtained with slight decrease in microhardness at different locations on the plate. Besides, significant reduction in hardness for BMG 2, BMG 10, and BMG 11 specimens is observed due to HPT processing from central to peripheral region of the disc. Present study shows that ACC HPT more intensively transform the structure of BMG in comparison to that of conventional HPT.

Combinatorial development and assessment of a Zr-based metallic glass for prospective biomedical applications

In the quest of corrosion-resistant biomaterials, the emergence of metallic glasses is a welcome stimulus, however, their progress is potentially impeded by the complex fabrication routes. This paper explores a Zr40Ti35Ni14Nb11 metallic glass, developed through combinatorial magnetron co-sputtering. Structural characterization of the system via Grazing-Incidence X-Ray Diffraction and Transmission Electron Microscopy coupled with Fourier Transformation demonstrate single phase homogeneous amorphous structure. The metallic glass, upon comparative electrochemical examination in physiological solution, displays relatively better corrosion resistance properties than conventional biomaterials, i.e. stainless steel 316L and commercially pure titanium, by an order of magnitude lower corrosion current density, (17 nA/cm2), lower passive current density (3.1 μA/cm2), invulnerability to pitting corrosion and one-order higher charge transfer resistance (6.9 MΩ·cm2). The superior corrosion resistance properties are ascribed to the synergistic effect of chemically and structurally homogeneous amorphous structure and protective passive film, enriched with chemically stable oxides of Zr and Ti. Mechanical characterization of the metallic glass via nanoindentation studies reveal high hardness (7.1 GPa) and fairly low elastic modulus (121.7 GPa), making it a candidate material for bioimplants.

A combinatorially developed Zr-Ti-Fe-Al metallic glass with outstanding corrosion resistance for implantable medical devices

This paper explores a Zr-Ti-Fe-Al metallic glass, fabricated via combinatorial approach using magnetron co-sputtering. The paradigm of combinatorial synthesis is demonstrated via X-Ray Diffraction and Transmission Electron Microscopy. The metallic glass is probed electrochemically in contrast with a distinguished biomaterial, commercially pure titanium (cp-Ti). The metallic glass shows no susceptibility to pitting corrosion and manifests better corrosion resistance properties than cp-Ti in terms of roughly one order improvement in corrosion current density and charge transfer resistance, attributed to the combined role of homogeneous amorphous structure and chemically stable oxide film predominantly composed of ZrO2 and TiO2.

Lithium polyacrylate-polyacrylamide blend as polymer electrolytes for solid-state electrochemical capacitors

A polymer electrolyte was developed by blending lithium (LiPAA) with non-ionic polyacrylamide (PAM). The LiPAA-PAM showed synergic effect and achieved an ionic conductivity of 13.8 ± 2.4 mS cm−1, higher than previously developed neutral pH polymer electrolytes. Chemical and structural characterizations of the LiPAA-PAM films revealed a stable homogeneous amorphous structure. The performance of double layer capacitors using LiPAA-PAM electrolyte system was demonstrated using YP-50F activated carbon electrodes. These solid cells demonstrated wide voltage window (1.5 V), good cycle life (>10,000 cycles), and excellent rate capability (up to 500 mV s−1 in cyclic voltammetry).

Specimen preparation for nano-scale investigation of cementitious repair material

Cementitious Repair Materials (CRMs) in the construction industry have been used for many decades now and has become a very important part of activities in cement world. The performance of some of these CRMs when applied to retrofitting concrete structural elements is also well documented. However, the characterization of some of the CRMs at the micro- and nano level is not fully documented. The first step to studying materials at the microscopic level is to be able to fabricate proper specimens for microscopy. In this study, a special and newly developed class of CRM was selected and fabricated by Focused Ion Beam (FIB) using well-known “Lift-out” technique. The prepared specimen was later examined using various analytical techniques such as energy dispersive x-ray analysis using one of the highest and most stable Scanning Transmission Electron Holography Microscopy (STEHM) around the world. This process enabled understanding of the composition, morphology, and spatial distribution of various phases of the CRM. It was observed that the microstructure consisted of a very fine, compact, and homogenous amorphous structure. X-ray analysis indicated that there was considerable deviation between the Si/Ca ratios for the hydrated product.

Thermal stability of the Ti-Zr-Cu-Pd nano-glassy thin films

Nano-glassy thin films consist of nanometer-sized glassy regions (clusters) with a structure corresponding to melt-quenched glasses and amorphous interfacial regions characterized by a reduced density, or locally enhanced free volume, and in many cases a modified chemical composition. Ti-Zr-Cu-Pd nano-glass thin films were synthesized by using direct current (DC) magnetron sputtering on Si substrates. The influence of the sputtering conditions (sputtering power and Ar gas pressure) on the nano- and microstructure of deposited films and on their thermal behavior was analyzed. The thin films were noted to exhibit a homogeneous amorphous structure when sputtered at low Ar pressure (0.2 Pa) and a nano-glass structure with various sizes of the glassy cluster at higher Ar pressures (0.5–0.8 Pa). By raising the Ar pressure, the average size of the glassy clusters was noted to decrease corresponding to an increase of the volume fraction of the interfacial regions. The glass transition and crystallization temperatures were determined by using differential scanning calorimetry (DSC) at heating rates up to 40 Kmin−1. The thermal stability of the thin films was studied by annealing at temperatures above the glass transition and crystallization temperatures. The microstructure of the thin films was studied by means of X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy. The results obtained indicate that the nano-glassy thin films exhibit higher thermal stability than homogeneous glassy thin films. The fact that an increase of the volume fraction of the interfacial component in nano-glassy thin films results in an ultra-stable thermal behavior is indicating that the presence of nano-glassy interfaces impedes crystallization.

Amorphous lead oxide (a-PbO): suppression of signal lag via engineering of the layer structure

Presence of a signal lag is a bottle neck of performance for many non-crystalline materials, considered for dynamic radiation sensing. Due to inadequate lag-related temporal performance, polycrystalline layers of CdZnTe, PbI2, HgI2 and PbO are not practically utilized, despite their superior X-ray sensitivity and low production cost (even for large area detectors). In the current manuscript, we show that a technological step to replace nonhomogeneous disorder in polycrystalline PbO with homogeneous amorphous PbO structure suppresses signal lag and improves time response to X-ray irradiation. In addition, the newly developed amorphous lead oxide (a-PbO) possesses superior X-ray sensitivity in terms of electron-hole pair creation energy {W}_{pm } in comparison with amorphous selenium – currently the only photoconductor used as an X-ray-to-charge transducer in the state-of-the-art direct conversion X-ray medical imaging systems. The proposed advances of the deposition process are low cost, easy to implement and with certain customization might potentially be applied to other materials, thus paving the way to their wide-range commercial use.

Noble‐Metal‐Free Metallic Glass as a Highly Active and Stable Bifunctional Electrocatalyst for Water Splitting

Many transition metals and alloys are expected to have high catalytic activities because of incompletely filled d orbitals for readily giving and taking electrons. However, the poor corrosion resistance, originating from high chemical activity, limits their applications as electrocatalysts for reactions in acidic and alkaline electrolytes. In this study, it is found that homogeneous amorphous structure can effectively decouple the intertangling catalytic activities and electrochemical stability of transition metal alloys. A noble‐metal‐free Ni40Fe40P20 metallic glass shows superior catalytic activities and high corrosion resistance, in comparison with the crystallized counterpart and other nanostructured noble‐metal‐based catalysts, for electrochemical water splitting in both acidic and alkaline solutions.

Block copolymers containing polyacrylamide and polyacrylic acid: Bulk structure and hydrogen bonds system

ABSTRACTAsymmetric block copolymers PAAc-b-PAAm (DBCs) and PAAm-b-PAAc-b-PAAm (TBCs) comprised poly(acrylic acid) blocks of constant chain length and polyacrylamide blocks of variable chain length were synthesized using RAFT/MADIX technique. Their properties in a bulk state were studied by differential scanning calorimetry and the hydrogen bond system was investigated by Fourier transform infrared spectroscopy. It was found that DBCs and TBCs possess a homogeneous amorphous structure, whose temperatures of glass transition and destruction beginning increased with growth of PAAm block length. The H-bond system between PAAc and PAAm blocks was most developed in TBC sample and formed manly by the mixed cyclic dimmers of carboxyl and amide groups.

Thin film GaP for solar cell application

A new approach to the silicon based heterostructures technology consisting of the growth of III-V compounds (GaP) on a silicon substrate by low-temperature plasma enhanced atomic layer deposition (PE-ALD) is proposed. The basic idea of the method is to use a time modulation of the growth process, i.e. time separated stages of atoms or precursors transport to the growing surface, migration over the surface, and crystal lattice relaxation for each monolayer. The GaP layers were grown on Si substrates by PE-ALD at 350°C with phosphine (PH3) and trimethylgallium (TMG) as sources of III and V atoms. Scanning and transmission electron microscopy demonstrate that the grown GaP films have homogeneous amorphous structure, smooth surface and a sharp GaP/Si interface. The GaP/Si heterostructures obtained by PE-ALD compare favourably to that conventionally grown by molecular beam epitaxy (MBE). Indeed, spectroscopic ellipsometry measurements indicate similar interband optical absorption while photoluminescence measurements indicate higher charge carrier effective lifetime. The better passivation properties of GaP layers grown by PE-ALD demonstrate a potential of this technology for new silicon based photovoltaic heterostructure

Characteristics of Al2O3/ZrO2 laminated films deposited by ozone-based atomic layer deposition for organic device encapsulation

We investigated the characteristics of 100nm-thick Al2O3/ZrO2 laminated films grown by ozone (O3)-based atomic layer deposition (ALD) at low temperature (100°C) as thin film encapsulation (TFE). Calcium (Ca) test was performed at a relative humidity (RH) of 50% with a temperature of 50°C to derive the water vapor transmission rates (WVTRs) of aluminum oxide (Al2O3)-, zirconium oxide (ZrO2)-, and Al2O3/ZrO2-laminated films. Al2O3/ZrO2-laminated films exhibited better permeation barrier properties than Al2O3 or ZrO2 single layer films. In Al2O3/ZrO2 laminated films, permeation barrier properties improved as the number of alternating layers increased. Permeation barrier properties were closely related to the number of interfaces because of the ZrAlxOy phase that formed at the interface between the Al2O3 and ZrO2 sublayers. The ZrAlxOy phase was denser than single layers of Al2O3 and ZrO2 and had a homogeneous amorphous structure. The formation of a ZrAlxOy phase in Al2O3/ZrO2 laminated film effectively improved the permeation barrier properties of the film.

Decomposition of amorphous Si2C by thermal annealing

In the present paper, the decomposition and the crystallization behaviour of amorphous Si2C films, which were deposited by r.f. magnetron co-sputtering on Si wafer substrates, are investigated. For analysis, the following methods were used: x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), grazing incidence x-ray diffractometry (GIXRD), atomic force microscopy and scanning electron microscopy. After deposition, the films exhibited a homogenous amorphous structure with a variety of bonding states reaching from homonuclear silicon-like Si-Si bonds over mixed Si-Si-C bonds to heteronuclear Si-C bonds. Annealing at 1200°C for 2h leads to the crystallization of silicon and silicon carbide with grain diameters of several nanometers within the amorphous matrix, as evidenced by GIXRD and TEM. With XPS also a distinct change of the bonding states is detected. After 2h of annealing, only Si-Si and Si-C bonds are detectable. After prolonged annealing at 1200°C for 20h, XPS shows only Si-C bonding states but no more Si-Si bonding. In addition, GIXRD verifies the absence of any polycrystalline silicon in the film. The microstructure of the film changed dramatically towards a jagged and porous structure. The vanishing of silicon during isothermal annealing is explained on base of in situ and ex situ TEM measurements, and a possible model for decomposition is suggested.

Phase separation in Zr56-xGdxCo28Al16 metallic glasses (0 ⩽ x ⩽ 20)

The influence of Gd addition on the microstructure of Zr56Co28Al16 metallic glasses was investigated for the exchange of Zr by up to 20 at.% Gd. Due to the large positive enthalpy of mixing between Zr and Gd, liquid–liquid phase separation occurs during rapid quenching of the melt. For a low concentration of Gd (x=2 at.%), a homogeneous amorphous structure is obtained for the as-quenched state. Early stages of spinodal decomposition are observed in the as-quenched state of the glasses with x=5 and 10 at.% Gd. Gd-enriched clusters 4–7nm in size are formed, as shown by atom probe tomography (APT). Annealing below the crystallization temperature Tx leads to an increase in the amplitude of compositional fluctuations and the analysis of the spatial atomic distribution by APT provides direct evidence of the spinodal character of the decomposition by uphill diffusion of Gd into the clusters. For higher Gd content (x=15 and 20 at.%), a coarsened microstructure of the phase-separated glass is obtained due to growth and coalescence while quenching the melt. The microstructure formation is essentially determined by the thermodynamic properties of the metastable undercooled liquid.

On the role of Ta cap in the recrystallization process of CoFeB layers

To understand the role of Ta capping on the tunneling magnetoresistance of CoFeB/MgO/CoFeB tunnel junctions, we performed an atom probe study on model CoFeB/Ta junctions. In as-prepared state, CoFeB exhibits chemically and structurally homogeneous amorphous structure. The nanoanalysis demonstrates that B segregation to the Ta cap enforces crystallization to start at the opposite interface towards the MgO barrier and so warrants the correct orientation relation. Carrying out isothermal and isochronal heat treatments, the diffusion coefficient of Boron in amorphous CoFeB could be determined.

Catalysis, nanostructure and macroscopic property triangle in bioactive calcium-containing ceramic systems

Calcium silicate ceramics are intended for application as long-term implant materials. In the present work, attention was paid to understand the correlations between the nanostructure (aggregate size, crystallinity, porosity) and the macroscopic properties (solubility in water and simulated body fluids, SBF; hardness) varying the chemical composition. Varying the catalyst (from a base to various acids) during the chemical synthesis was shown to significantly impact on the pore size, crystallinity and mechanical properties. The basic catalyst yields the ceramics with the highest mechanical strength. Ammonia used in 1.0 or 10.0 molar ratio results in bulk ceramics with parameters required for a biomedical application, good hardness (180–200 HV) and low solubility (1–3%) in water and in SBF. The fine porosity (~50nm) and homogeneous amorphous structure induce good mechanical character.

New Zr-based glass-forming alloys containing Gd and Sm

The effect of minor additions of Gd and Sm on the glass-forming ability (GFA) of Cu-Zr-Al alloys is investigated here. The rationale for these additions is the fact that the atomic size distribution can increase GFA by changing the topology of the alloy as a function of cluster stability, which is tied to the electronegativity and ionic and covalent nature of alloys. Ingots with nominal compositions of Cu40Zr49Al10.5Gd0.5, Cu40Zr49Al10.5Sm0.5 and Cu39Zr50Al9Gd2 were prepared by arc-melting and rapidly quenched ribbons were produced by the melt-spinning technique. Bulk samples with a thickness of up to 10 mm were also produced by casting, using a wedge-shaped copper mold. The samples were characterized by differential scanning calorimetry, X-ray diffractometry and scanning electron microscopy. The three compositions showed a fully amorphous structure in the ribbons and a predominantly homogeneous amorphous structure with a thickness of up to 10 mm, although some gadolinium oxide crystals as well as samarium compounds were found to be scattered in the amorphous matrix in 5-mm-thick samples. The amorphous phases in the alloys showed high thermal stability with a supercooled liquid region (ΔTx) of about 70 K.

Thermal stability of magnetron sputtered amorphous Si2C

The thermal stability of amorphous Si2C films was studied by means of X-ray Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES), Grazing Incidence X-ray Diffractometry (GIXRD), Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). The films were deposited by magnetron sputtering onto silicon single crystals. The as-deposited films show a homogenous amorphous structure with a variety of bonding states reaching from homonuclear silicon-like SiSi over mixed SiSiC to heteronuclear SiC bonds. Annealing at 800°C for 1h leads to a depletion of SiSiC bonding states and to the formation of additional SiC bonds. AFM and SEM images showed particles with a remarkable faceting on the surface of the annealed film. In accordance with GIXRD and AES measurements, these observations confirmed the crystallization of silicon during thermal annealing. Besides, no crystallized silicon carbide could be detected.