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This paper presents a microstructural study of laser micro-processed high-purity CuZrAl alloys prepared by arc melting and Cu-mould casting. Microprocessing of the CuZrAl alloy was performed using a Rofin DC-015 diffusion-cooled CO slab laser system with 10.6-μm wavelength. The laser was defocused to a spot size of 0.2 mm on the sample surface. The laser parameters were set to give 300- and 350-W peak power, 30% duty cycle and a 3000-Hz laser pulse repetition frequency (PRF). About 100-micrometer-wide channels were scribed on the surfaces of disk-shaped amorphous and partially crystalline samples at traverse speeds of 500 and 5000 mm/min. These channels were analysed using scanning electron microscopy (SEM) and 2D stylus profilometry. The metallographic study and profile of these processed regions are discussed in terms of the applied laser processing parameters. The SEM micrographs showed that striation marks developed at the edge and inside these regions as a result of the laser processing. The results from this work showed that microscale features can be produced on the surface of amorphous Cu-Zr-Al alloys by CO laser processing. [ABSTRACT FROM AUTHOR]

The oxidation of the bulk amorphous alloy Zr65Cu17.5Ni10Al7.5 in air in its amorphous and the supercooled liquid states was studied in the temperature range 573–663 K using X-ray photoelectron spectroscopy (XPS). The oxide film mainly consisted of the oxides of Zr (as ZrO2) and Al (as Al2O3). No Cu or Ni was found in the oxide film formed on the amorphous state of the alloy while significant Cu (as CuO) was present in the oxide film formed on the alloy in its supercooled liquid state. The role of the various alloying elements during oxidation at high temperatures in air is discussed in the paper. The XPS data from oxide film support the previously suggested mechanism for oxidation of this alloy, i.e. the rate controlling process during oxidation of the alloy at low temperatures (in the amorphous state) is the back-diffusion of Ni and Cu, while the oxidation at high temperatures (in the supercooled liquid state) is dominated by the inward diffusion of oxygen. [ABSTRACT FROM AUTHOR]

This paper describes original experimental results obtained in a study of the rheological behavior of amorphous bulk Vitralloy 1 (Zr41Ti14Cu12.5Ni10Be22.5), which shows linear viscous (Newtonian) flow over a certain range of deformation rates. These results were compared against results obtained for other superplastic alloys, and against results obtained for metal melts during the crystallization process. [ABSTRACT FROM AUTHOR]

Minor alloying addition or microalloying technology has already shown dramatic effects on glass formation and thermal stability of bulk metallic glasses (BMGs). This paper intends to provide a comprehensive review of recent developments of this technology in the field of BMGs. The beneficial effects of minor alloying additions on the glass formation and the thermal stability of BMGs will be summarized and analyzed. In addition, principles and guidelines for future application of this technology will also be proposed. [ABSTRACT FROM AUTHOR]

The crevice corrosion behaviors of an Fe-based bulk metallic glass alloy (SAM1651) and a Ni-Cr-Mo crystalline alloy (C-22) were studied in 4M NaCl solution at 100 °C with cyclic potentiodynamic polarization and constant-potential tests. The corrosion damage morphologies, corrosion products, and the compositions of corroded surfaces of these two alloys were studied with optical three-dimensional reconstruction, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Auger electron spectroscopy (AES). It was found that the Fe-based bulk metallic glass (amorphous alloy) SAM1651 had a more positive breakdown potential and repassivation potential than crystalline alloy C-22 in cyclic potentiodynamic polarization tests and required a more positive oxidizing potential to initiate crevice corrosion in constant-potential tests. Once crevice corrosion initiated, the corrosion propagation of C-22 was more localized near the crevice border compared to SAM1651, and SAM1651 repassivated more readily than C-22. The EDS results indicated that the corrosion products of both alloys contained a high amount of O and were enriched in Mo and Cr. The AES results indicated that a Cr-rich oxide passive film was formed on the surfaces of both alloys, and both alloys corroded congruently in the crevice corrosion damage areas. [ABSTRACT FROM AUTHOR]

The wear and the high-temperature oxidation resistance of the D2 steel (Fe-1.5 C-12 Cr-0.95 Mo-0.9 V-0.3 Mn) were increased by laser surface alloying after coating the surface with SiC or Cr3C2 powder. The surface alloys exhibit two microstructures: hypoeutectic and hypereutectic, respectively, all containing iron solid solutions and iron-chromium carbides, (Fe,Cr)7C3. The oxidation resistance of these alloys was measured in isothermal and cyclic conditions, and was shown to increase with silicon or chromium additions, particularly due to the formation of a chromia scale with excellent behaviour during thermal shoks. The surface alloy obtained with Cr3C2 also has shown a better resistance to wear due to its hypereutectic microstructure. [ABSTRACT FROM AUTHOR]

Order and disorder are important principles in materials science in which entropy is a measure of disorder in a system. For example, recently developed high-entropy alloys and amorphous alloys have drawn interest based on the ability to design their disorder to bring out different material characteristics. High-entropy alloys are controlled by chemical disorder, whereas amorphous alloys are governed by topological disorder. There is often a need to increase disorder or entropy in these materials to satisfy certain complex performance requirements. Here, we examine the roles of order, disorder, and entropy in amorphous and high-entropy alloys. Several key research topics are summarized, including high-entropy films, high-entropy ceramics, and high-entropy alloys. Moreover, there remain questions about the role of entropy stabilization in high-entropy ceramics. Here, we also report three novel porous light-weight high-entropy nitrides based on the NbTiAlSi system. Our findings clarify the general role of entropy in high-entropy ceramics. [ABSTRACT FROM AUTHOR]

Using a combination of extended X-ray absorption fine structure measurements, stochastic quenching (SQ) calculations and Voronoi tessellation analysis, the local atomic environments in thin films of amorphous Sm x Co 1 - x ( x = 0.10, 0.22 and 0.35) are investigated and also compared with crystalline stoichiometric Sm–Co alloys of similar compositions. It is found that the variations in local environment around Co atoms in the amorphous films increase with increasing x and that none of the films exhibit any pronounced short-range order around the Sm atoms. There are, however, signs of clustering of Sm atoms in the SQ-generated simulated amorphous materials. Furthermore, good agreement is observed between experimentally obtained parameters, e.g., interatomic distances and coordination numbers, and those extracted from the simulated alloys. This is a strong indication that SQ provides a powerful route to reliable local structure information for amorphous rare earth–transition metal alloys and that it could be used for designing materials with properties that meet the demands of specific applications. [ABSTRACT FROM AUTHOR]

A new Mg-based bulk amorphous alloy (i.e., Mg65Cu25Gd10) has successfully been developed by Men and Kim [H. Men and D.H. Kim, J. Mater. Res. 18, 1502 (2003)]. They showed that this alloy exhibits significantly improved glass-forming ability (GFA) in comparison with Mg65Cu25Y10 alloy. However, this improved GFA cannot be indicated by the supercooled liquid region ΔT and the reduced glass-transition temperature Trg. As shown in the current comment, the new parameter γ, Tx/(Tg + T1) defined in our recent papers [Z.P. Lu and C.T. Liu, Acta Mater. 50, 3501 (2002); Z.P. Lu and C.T. Liu, Phys. Rev. Lett. 91, 115505 (2003)] can well gauge GFA for bulk metallic glasses, including the current Mg-based alloys. [ABSTRACT FROM AUTHOR]

Electrochemical micromachining (ECMM) with microtool electrodes is a promising method for microshaping bulk metallic glasses (BMGs) at room temperature. A key challenge is the control of the electrode reactions to impede the disturbing passive layer formation on machined surface regions. In the example case of a Fe-based glassy Fe65.5Cr4Mo4Ga4P12C5B5.5 alloy, it will be demonstrated that by using an aqueous electrolyte based on 0.1 M H2SO4 solution with up to 0.1 M Fe2(SO4)3 addition and by applying ultrashort voltage pulses, complex microstructures can be machined with high precision. Potentiodynamic polarization measurements reveal that the salt addition reduces the charge transfer resistance of the microtool and therefore, the negative bias potential effect. The free corrosion and passive state of the BMG workpiece are affected, but not the transpassive regime. Systematic ECMM studies were conducted to obtain optimum parameters for shaping complex lateral structures with very smooth and well-defined machining areas. [ABSTRACT FROM PUBLISHER]

This article is a brief review of new different ways to tailor the magnetic properties of amorphous ferromagnetic microwires of two types: glass-coated and glassless. Metallic core of the studied samples was manufactured from CoFe-, Co-, and CoFeNi-based alloys by quenching and drawing or by the Taylor-Ulitovsky methods. We tested the following options to tailor the magnetic properties: changing of the parameters of manufacturing process, annealing, magnetostatic interaction in the array of wires. For the first time, it was found that a system of Co-based microwires with nearly zero magnetostriction coefficient exhibits a step-like hysteresis loop. The same behavior was found for single microwires with compositions of Fe Si B and Fe Co Si B produced under certain conditions. The effect of stress-annealing was investigated for Fe Co BSi , Fe Co BSi , and Fe Co BSi glass-coated microwires. [ABSTRACT FROM AUTHOR]

It is known that the glass forming-ability (GFA) of bulk metallic glasses (BMGs) can be greatly enhanced via minor element additions. However, direct evidence has been lacking to reveal its structural origin despite different theories hitherto proposed. Through the high-resolution transmission-electron-microscopy (HRTEM) analysis, here we show that the content of local crystal-like orders increases significantly in a Cu-Zr-Al BMG after a 2-at% Y addition. Contrasting the previous studies, our current results indicate that the formation of crystal-like order at the atomic scale plays an important role in enhancing the GFA of the Cu-Zr-Al base BMG. [ABSTRACT FROM AUTHOR]

Monte Carlo method has been performed to simulate the structure evolution of Ni-Cu alloy nanorods encapsulated in the carbon nanotube and removed from the carbon nanotube. The Sutton-Chen many-body potential and Lennard-Jones potential are used to describe the metal-metal and metal-carbon interactions, respectively. The studies show that all Ni-Cu atoms in carbon nanotube are arranged in a series of concentric cylindrical layers even they have different fractions, and Cu atoms are apt to stay at the surface layers. If the carbon nanotube was removed, Ni-Cu alloy nanorod would turn into a cluster with nickel core and copper shell. The physical origin for such structure formation and evolution toward core-shell motifs are discussed. The bond pair analysis shows that the nanorods and clusters are amorphous structures dominated by the rhombohedral structure and mixed up with some local short-range order. [ABSTRACT FROM AUTHOR]

A magnetoimpedance effect is observed in Co80–xNixB20 ( x = 4, 6, 8, 10, 12) amorphous metal alloy ribbons when an alternating current at frequencies ranging from 1–3000 kHz is passed through samples in an external magnetic field. Spectra of the permittivity and optical conductivity of the surface of ribbons of these alloys are obtained for incident photon energies of 1.0–5.0 eV. The relationships between the magnitude of the magnetoimpedance effect, and the magnetic properties, electronic structure parameters, and optical characteristics of the amorphous alloy samples are determined. [ABSTRACT FROM AUTHOR]

Nitinol, a group of nearly equiatomic Ni-Ti alloys, steadily conquers new areas of application. Because of the need to keep a low profile of miniature implant devices, and considering the lack of compatibility between Nitinol superelasticity and the mechanical properties of traditional coatings, bare surfaces are of interest. In this article, an overview of our studies of bare Nitinol surfaces is presented, and the performance of coated surfaces is outlined. Together dense and porous Nitinol offer a wide array of surface topographies, suitable for attachment and migration of biological cells and tissue ingrowth. Native Nitinol surface oxides vary from amorphous to crystalline and exhibit semiconducting properties associated with better blood compatibility. Nitinol surfaces are analyzed with regard to high and lasting nickel release in vitro. Surface oxide thickness and Nitinol intermetallic particulates are discussed in relation to corrosion resistance and mechanical performance of the material. [ABSTRACT FROM AUTHOR]

Iron (Fe)-based amorphous alloys possess enhanced hardness and are highly resistant to corrosion, which make them desirable for wear applications in corrosive environments. It was of interest to examine the behavior of amorphous alloys during anodic polarization in concentrated salt solutions and in the salt-fog testing. Results from the testing of one amorphous material (SAM2X5) both in ribbon form and as an applied coating are reported here. Cyclic polarization tests were performed on SAM2X5 ribbon as well as on other nuclear engineering materials. SAM2X5 showed the highest resistance to localized corrosion in 5 M CaCl2 solution at 105 °C. Salt fog tests of 316L SS and alloy 22 coupons coated with amorphous SAM2X5 powder showed resistance to rusting. Partial devitrification may be responsible for isolated pinpoint rust spots in some coatings. [ABSTRACT FROM AUTHOR]

ZrTiAlCuNi films are deposited by plasma sputtering from an alloyed target prepared by induction – cold crucible melting method. The films are found to be amorphous and exhibit a composition very similar to the target one. It is shown that the amorphous character of the deposits is rather due to the high glass forming ability (GFA) of the Zr-based alloy system, than to the deposition method used. The sputtering process of the alloyed target, composed of mixed Zr-containing phases, has been studied. It appears to be a global process leading to a quasi-congruent transfer of the target elements into the film. [ABSTRACT FROM AUTHOR]

Unlike the well-defined long-range order that characterizes crystalline metals, the atomic arrangements in amorphous alloys remain mysterious at present. Despite intense research activity on metallic glasses and relentless pursuit of their structural description, the details of how the atoms are packed in amorphous metals are generally far less understood than for the case of network-forming glasses. Here we use a combination of state-of-the-art experimental and computational techniques to resolve the atomic-level structure of amorphous alloys. By analysing a range of model binary systems that involve different chemistry and atomic size ratios, we elucidate the different types of short-range order as well as the nature of the medium-range order. Our findings provide a reality check for the atomic structural models proposed over the years, and have implications for understanding the nature, forming ability and properties of metallic glasses. [ABSTRACT FROM AUTHOR]

We report experimental evidence of in-situ Mg77Cu12Zn5Y6 bulk metallic glass (BMG) matrix composite with extraordinary plastic strain of 18.5% and specific strength of 4.31 x 105 N·m·kg¹, which are the highest plasticity and specific strength in Mg base BMG alloys reported to date. The excellent mechanical properties are attributed to the formation of the composite structure which is composed of amorphous matrix and hexagonal-close-packed (hcp) Mg solid solution needle phase with a width less than 500 nm. As plastic phase, the Mg needles not only possess the capability of deformation but also have work hardening phenomenon effect. They give rise to multiple shear bands, and hinder the propagation of local shear band in amorphous matrix. [ABSTRACT FROM AUTHOR]

The structural, electrical and optical properties of the phase change alloy AgSbSe2 were investigated and compared with its Te-based counterpart AgSbTe2. A huge electrical resistance change of more than four orders of magnitude is probed during the amorphous-to-crystalline transition, accompanied with high optical contrast and small volume change. Furthermore, recrystallization can be realized within 10 ns, which could be correlated with the observed low transition temperature and the simple NaCl-type crystalline structure. These properties indicate that Se-based alloys might be suitable materials for phase change recording, replacing Te based alloys. [ABSTRACT FROM AUTHOR]

Bulk metallic glasses are commonly produced by the rapid cooling of liquid alloys. They have emerged over the past decade as a novel class of materials, with attractive properties and technological promise. The bulk metallic glasses so far produced contain three or more component elements. These complex compositions are necessary to frustrate the crystallization of the liquid melt on cooling, but can also lead to phase separation, which is detrimental to the thermal and mechanical properties of metallic glasses. Here we report, using X-ray diffraction measurements, the formation of a bulk metallic glass from elemental zirconium at high static pressures and low temperatures (relative to its melting temperature at atmospheric pressure). Amorphous zirconium can be recovered at ambient conditions and demonstrates a superior thermal stability compared to amorphous alloys, which could lead to new high-temperature applications of amorphous metals. [ABSTRACT FROM AUTHOR]

Inverted hysteresis loops were observed for the first time in the near-surface layers of heterogeneous (nanocrystalline/amorphous) Fe81Nb7B12 alloys. In particular, a negative residual magnetization is retained when a positive magnetic field applied in the sample plane is decreased to zero. The inverted hysteresis is qualitatively explained within the framework of a two-phase model, according to which the heterogeneous alloys contain two dissimilar phases exhibiting uniaxial magnetic anisotropy and featuring antiferromagnetic exchange interaction. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

A model fluid system whose intermolecular forces consist of the short range part characterizing usual stable fluid and the long range part of Kac-type is considered. When the ratio of the force ranges is large enough, the system can be described by regarding the system having only short range interactions as a reference fluid treated as a continuum, on which long range forces acting among tiny fluid elements are superimposed. We discuss the glassy behavior of this model relating it to the mode coupling theory and using real replica theory. These theories lead to the two equations for non-ergodicity parameter which are totally different from each other. We argue that our model can be a basis for examining nature of the drastic approximations entering derivations of the mode coupling equations. We further explore the possibility of developing the dynamical real replica approach for our model system with the hope of providing a framework to cope with different time scales characterizing complex glassy behavior. [ABSTRACT FROM AUTHOR]

Crystallization of Co-rich amorphous alloys via thermal and laser annealing has been studied using X-ray diffraction and high resolution electron microscopy techniques. It has been found that microstructural properties of the resulting alloys can differ significantly for the two thermal treatments depending on their Co content. Co78Fe2Mn2Si9B9, Co72Fe8B20 and Co50Fe28Si10B12 amorphous alloys have been studied and only Co72Fe8B20 has shown very different crystallization processes after thermal and laser annealing. The results of comparative analysis of the influence of laser and thermal annealing on optical and structural properties of the samples are discussed. [ABSTRACT FROM AUTHOR]

Fractographic studies of ductile shear failure under the uniaxial compression for rod–like samples of the Zr41.2Ti13.8Ni10Cu12.5Be22.5 and Cu50Zr35Ti8Hf5Ni2 bulk amorphous alloys at temperatures 300 and 77 K are presented. The mechanisms of shear deformation and failure appeared to have characteristics in common with other amorphous alloys prepared in the form of thin ribbons. However, there were a number of new fractographic features observed due to the bulk character of the samples and to the large supercooled liquid region of these alloys. [ABSTRACT FROM AUTHOR]

Abstract. The amorphous non-equilibrium state of the system Fe/AI is studied in bulk and thin-film systems. For bulk samples prepared by ion-beam mixing of laser-deposited multilayers, a bec solid solution is found for alloys with up to 70 at. % Al. Around 75 at. % Al a Fe[sub 2]Al[sub 5]-like crystalline phase is found. An amorphous state with Fe[sub 2]Al[sub 5]-like short-range order is found for 80 at. % Al. In thin films, for example the amorphous Al-rich transition layer of a laser-deposited Fe/Al multilayer, the amorphous state can exist for up to 30 at. % Fe due to the high interfacial energy. By ion-beam mixing at low temperatures (about 140 K) an oversaturation with 40 at. % Fe can be achieved. PACS: 68.55.-a; 61.82.Bg [ABSTRACT FROM AUTHOR]

This work studies the influence of the Ag admixtures on the crystallization of the amorphous Fe75Si9B16 alloy, with the aid of electric and magnetic measurements. It is concluded that the solid solubility of the Ag in these alloys is very small, reaching 2 at% at most. Because of microsegregation, the presence of even these minimal admixtures accelerates the crystallization procedure. [ABSTRACT FROM AUTHOR]

A theoretical model which effectively describes a novel micromechanism of solid-state amorphization in mechanically alloyed metallic materials is proposed. Within the model the amorphous phase nucleates as a result of the intersection of a grain boundary by a plastic-shear microband. It is shown that the growth of a nucleus of the amorphous α - β alloy near a site on a grain boundary intersected by a shear microband is effectively controlled by the rate of diffusion mixing of atoms of the mechanically alloyed metals α and β. [ABSTRACT FROM AUTHOR]