Mechanical properties of bulk metallic glasses

The mechanical properties of bulk metallic glasses, including their superior strength and hardness, and excellent corrosion and wear resistance, combined with their general inability to undergo homogeneous plastic deformation have been a subject of fascination for scientists and engineers. The scientific interest stems from the unconventional deformation and failure initiation mechanisms in this class of materials in which the typical carriers of plastic flow (dislocations) are absent. Metallic glasses undergo highly localized, heterogeneous deformation by formation of shear bands, a particular mode of deformation of interest for certain applications, but which also causes them to fail catastrophically due to uninhibited shear band propagation. Varying degrees of brittle and plastic failure creating intricate fracture patterns are observed in metallic glasses, quite different from those observed in crystalline solids. The tension–compression anisotropy, strain-rate sensitivity, thermal stability, stress-induced crystallization and polyamorphism transformations, are some of the attributes that have sparked engineering studies on bulk metallic glasses. Understanding of the glass-forming ability and the deformation and failure mechanisms of bulk metallic glasses, has given insight into alloy compositions and intrinsically-forming or extrinsically-added reinforcement phases for creating composite structures, to attain the combination of high strength, tensile ductility, and fracture toughness needed for use in advanced structural applications. The relative ease of fabricating metallic glasses into bulk forms, combined with their unique mechanical properties, has made these materials attractive options for possible applications in aerospace, naval, sports equipment, luxury goods, armor and anti-armor systems, electronic packaging, and biomedical devices.     

The potential of Zr-based bulk metallic glasses as biomaterials

Zr-based bulk metallic glasses (BMGs) are a new type of metallic materials with disordered atomic structure that exhibit high strength and high elastic strain, relatively low Young’s modulus, and excellent corrosion resistance and biocompatibility. The combination of these unique properties makes the Zr-based BMGs very promising for biomaterials applications. In this review article, the authors give an overview of the recent progress in the study of biocompatibility of Zr-based BMGs, especially the relevant work that has been done in the metallic glasses group in Huazhong University of Science and Technology (HUST), including the development of Ni-free Zr-based BMGs, the mechanical and wear properties, the bio-corrosion resistance, the in vitro and in vivo biocompatibility and the bioactive surface modification of these newly developed BMGs.     

Metallic glasses from “alchemy” to pure science: Present and future of design,processing and applications of glassy metals

Metallic glasses, first discovered a half century ago, are currently among the most studied metallic materials. Available in sizes up to several centimeters, with many novel, applicable properties, metallic glasses have also been the focus of research advancing the understanding of liquids and of glasses in general.Metallic glasses (MGs), called also bulk metallic glasses (BMGs) (or glassy metals, amorphous metals, liquid metals) are considered to be the materials of the future. Due to their high strength, metallic glasses have a number of interesting applications, for example as coatings. Metallic glasses can also be corrosion resistant. Metallic glasses, and the crystalline materials derived from them, can have very good resistance to sliding and abrasive wear. Combined with their strength – and now, toughness – this makes them ideal candidates for bio-implants or military applications. Prestigious Journals such as “Nature Materials”, “Nature” frequently publish new findings on these unusual glass materials. Moreover Chinese and Asian scientists have also been showing an interest in the study of metallic glasses.This review paper is far from exhaustive, but tries to cover the areas of interest as it follows: a short history, the local structure of BMGs and the glass forming ability (GFA), BMGs’ properties, the manufacturing and some applications of BMGs and finally, about the future of BMGs as valuable materials.     

The potential of Zr-based bulk metallic glasses as biomaterials

Zr-based bulk metallic glasses (BMGs) are a new type of metallic materials with disordered atomic structure that exhibit high strength and high elastic strain, relatively low Young’s modulus, and excellent corrosion resistance and biocompatibility. The combination of these unique properties makes the Zr-based BMGs very promising for biomaterials applications. In this review article, the authors give an overview of the recent progress in the study of biocompatibility of Zr-based BMGs, especially the relevant work that has been done in the metallic glasses group in Huazhong University of Science and Technology (HUST), including the development of Ni-free Zr-based BMGs, the mechanical and wear properties, the bio-corrosion resistance, the in vitro and in vivo biocompatibility and the bioactive surface modification of these newly developed BMGs.     

Comparison of memory switching operation in a number of amorphous chalcogenide systems

A number of chalcogenide glasses were investigated for thin film switching applications. Two ranges of threshold voltage were of interest, 15 and 30 V. The switching performance of thin film devices was evaluated and rated on a simple numerical scale. The memory glasses based on the Ge-Te eutectic gave generally satisfactory performance. Selenium-based glasses exhibited high threshold voltage in thin film form, but had limited lifetime. Threshold voltages of about 30 V were obtained from Bi-As-Se glasses; these proved difficult to lock “ON” and possible reasons for this are discussed. Measurements on the bulk properties were used to give an indication of the properties to be expected from thin films of the corresponding glasses.     

Friction and Wear Behaviors of Nanostructured Metals

Nanostructured （ns） materials, i.e., polycrystalline materials with grain sizes in the nanometer regime （typically below 100 nm）, have drawn considerable attention in the past decades due to their unique properties such as high strength and hardness. Wear resistance of ns materials, one of the most important properties for engineering materials, has been extensively investigated in the past decades. Obvious differences have been identified in friction and wear behaviors Between the ns materials and their corresponding coarse-grained （cg） counterparts, consistently correlating with their unique structure characteristics and mechanical properties. On the other hand, the superior tribological properties of ns materials illustrate their potential applications under contact loads. The present overview will summarize the important progresses achieved on friction and wear behaviors of ns metallic materials, including ultrafine-grained （ufg） materials in recent years. Tribological properties and effects on friction and wear behaviors of ns materials will be discussed under different wear conditions including abrasive wear, sliding wear, and fretting wear. Their correlations with mechanical properties will be analyzed. Perspectives on development of this field will be highlighted as well.     

Thin film metallic glasses in optoelectronic,magnetic, and electronic applications: A recent update

Thin film metallic glass (TFMG) is a new class of metallic thin film with unique characteristics, including smooth surface, absence of grain boundaries, second-order glass transition, annealing-induced amorphization, soft magnetic properties, and high thermal stability. Hence, with these properties, TFMGs are found very useful and promising in many areas, ranging from structural, biomedical to electrical components. This review provides an update on future challenges and opportunities associated with the further development of TFMG.     

Tribological property enhancement of CrN films by metal vapor vacuum arc implantation of Vanadium and Carbon ions

CrN films have been extensively used in precision forming and molding applications because of their excellent tribological properties and oxidation-resisting characteristics. Vanadium and carbon ions are introduced into the near surface layer of deposited CrN films via metal vapor vacuum arc implantation to improve the wear performance of CrN films. Dense and smooth CrN film was deposited using a filtered arc deposition system, which provides fully ionized Cr plasma on the substrate surface. Subsequently, surface bombardment of the deposited CrN film with vanadium and carbon ions densifies the film and forms an alloy near the surface. These CrN-based films were characterized by X-ray photoelectron electron and Auger electron spectroscopies. Examinations of the tribological and mechanical film properties, including wear resistance, corrosion resistance and fracture toughness were performed and correlated with respect to the implantation parameters.     

Tantalum-based thin film coatings for wear resistant arthroprostheses

Cobalt-chromium-molybdenum alloys with high carbon content (HC-CoCrMo) are widely used as materials for arthroprosthesis, in particular in metal-on-metal (MoM) hip joints. In spite of their good wear and corrosion resistance, production of metallic wear particles and metal ion release will occur on a large time-scale. An enhancement of the metal ion level in the patient's blood and urine is often reported in clinical data. Hypersensitivity, inflammatory response and cell necrosis can occur as consequence. So implants on young patients and women on childbearing age are not so widespread. The aim of this research is the realization of a thin film coating in order to improve the biocompatibility of Co-based alloys and to reduce debris production, ion release and citotoxicity. The innovative process consists of a thermal treatment in molten salts, in order to obtain a tantalum enriched thin film coating. Tantalum is chosen because it is considered a biocompatible metal with high corrosion resistance and low ion release. Three HC-CoCrMo alloys, produced by different manufacturing processes, are tested as substrates. The coating is a thin film of TaC or it can be composed by a multilayer of two tantalum carbides and metallic tantalum, depending on the temperature of the treatment and on the carbon content of the substrate. The thin films as well the substrates are characterized from the structural, chemical and morphological point of view. Moreover mechanical behaviour of treated and untreated materials is analyzed by means of nanohardness, scratch and ball-on-disc wear tests. The coating increases the mechanical and tribological properties of HC-CoCrMo.     

Surface morphology,tribological properties and in vitro biocompatibility of nanostructured zirconia thin films

Deposition of nanostructured and low-wear zirconia (ZrO₂) thin films on the metallic component of a total joint implant is envisaged to reduce wear of the soft ultra-high molecular weight polyethylene (UHMWPE) counterpart. In this work, morphological surface features, wear resistance and in vitro-biocompatibility of zirconia thin films deposited by the novel Pulsed Plasma Deposition (PPD) method have been investigated. Film thickness, roughness and wettability were found to be strongly dependent on deposition gas pressure. Interestingly, wear rate of UHMWPE disks coupled to zirconia-coated titanium spheres was only poorly correlated to the contact angle values, while film roughness and thickness seemed not to affect it. Furthermore, wear of UHMWPE, when coupled with zirconia coated-titanium spheres, significantly decreased with respect to uncoated spheres under dry or NaCl-lubricated conditions; besides, when using bovine serum, similar results were obtained for coated and uncoated spheres. Finally, suitable mesenchymal stem and osteoblast cells adhesion, proliferation and viability were observed, suggesting good biocompatibility of the nanostructured zirconia films. Taken together, the results shown in this work indicate that zirconia thin films deposited by the PPD method deserve further investigations as low-wear materials for biomedical applications such as total joint replacement.     

Formation, Structure and Properties of Bulk Metallic Glasses

1.IntroductionTheformationofmetallicglassesbydirectquench-ingfromthemeltwasfirstdiscoveredin196obyDuwezandhisco-workersinaAu-25at.pctSialloy[']bya'guntechnique'[2].Thistechniqueen-abledcoolingrateoflo6K/s,thuscreatinganewseriesofmaterials.Thediscoveryofmetal1icglassesandmetastab1ephasehasledto-explosiveresearchanddevelopmefltofmetallicglassesandothercrys-tallinematerialsquenchedfrommelt[3'4].Metallicglasses,whichareobtainedbytherapidquenchingofmetallicmelts,arenoncrystallineoramorphous,likeo…     

Tribological properties of Cr-Si-N nanocomposite film adherent silicon under various environments

Chromium nitride thin films have good corrosion resistance and mechanical properties. However, their hardness is slightly lower than that of other hard coatings. The concept of nanocomposite thin films is employed by adding silicon to form Cr-Si-N thin films with enhanced hardness and wear resistance. In this study, Cr-Si-N films with various Si contents were coated on silicon wafer to enhance the tribological properties and anticorrosion by a bipolar symmetry pulsed DC reactive magnetron sputtering process. The tribological properties were studied by a pin-on-disk tester. The tests were conducted with the same operating condition under three different environments. They were performed in the ambient atmosphere (in 55% humid air), DI water, and 0.01 M NaCl aqueous solution, respectively. The wear tests revealed that, as the silicon content was increased, even though the Cr-Si-N films had a better anticorrosion property they had an inferior performance on wear resistance. The results were concluded to be mainly due to Cr-Si-N films’ microstructures and adhesion to the Si substrate rather than their hardness and toughness.     

Microscale deformation behavior of amorphous/nanocrystalline multilayered pillars

Metallic glasses have recently been extended their research and application in micro-electro-mechanical systems (MEMS). However, the brittle nature of metallic glasses in the bulk and thin film forms inevitably imposes limitation. The current study applies the new idea to adopt a thin layer of nanocrystalline metal film beneath the brittle binary ZrCu thin film metallic glass (TFMG) layer. This metal film needs to be sufficiently strong in modulus and strength and needs to be deposited with the appropriate film orientation. The face-centered cubic Cu {111} film appears to be too soft, the body-centered cubic Mo {110} film behaves to be too brittle, but the hexagonal close-packed Zr {0001} film matches all above requirements. The shear bands initiated in the ZrCu thin film metallic glass layer can be absorbed and accommodated by the nanocrystalline Zr {0001} layer via the nano-twinning mechanism. The original brittle ZrCu TFMG, with the inclusion of a Zr layer beneath, can behave highly ductile with semi-uniform plastic deformation of 55%, even more ductile than most pure metals. The amorphous-crystalline interface exhibits good strain compatibility after appreciable plastic deformation. This finding can impose great impact on the TFMG/metal multilayer structures useful for MEMS design.     

Electroless alloy/composite coatings: A review

Since the inception of electroless coating by Brenner & Riddell in 1946, it has been the subject of research interest and, in the past two decades, emphasis has shifted to the studies of its properties and applications. The co-deposition of paniculate matter or substance within the growing film has led to a new generation of electroless composite coatings, many of which possess excellent wear and corrosion resistance. This valuable process can coat not only electrically conductive materials including graphite but also fabrics, insulators like plastics, rubber etc. The low coating rates with these can provide better reflectivity of plated surfaces and many more applications. Coatings can be tailored for desired properties by selecting the composition of the coating alloy/composite/metallic to suit specific requirements. The market for these coatings is expanding fast as the potential applications are on the rise. In the present article, an attempt has been made to review different electroless alloy/composite coatings with respect to bath types and their composition, properties and applications. Different characterisation studies have been conducted on various electroless nickel-based coatings with emphasis on wear and corrosion properties.     

Ferroelectric films for non volatile-memory applications

Microelectronic applications of ferroelectric thin films have undergone a resurgence. Recent advances in deposition technologies and the achievement of bulk properties in thin films have enabled successful integration and fabrication of ferroelectric random access memories onto standard integrated circuits that combine high speed, complete non-volatility and extreme radiation hardness. Current research covers both the basic and applied areas in ferroelectric material science and semiconductor device development. In this talk the evolution of solid state memory devices in conjunction with silicon technology will be described, and the increasingly important role expected from ferroelectric materials highlighted. In coupling ferroelectric thin film processing with Si technology several new problems have to be resolved. The device physics and design, the material choice for ferroelectric memories, thin film preparation and characterization, and the problems of fatigue and retention will be discussed.     

Grain size and film thickness effect on the thermal expansion coefficient of FCC metallic thin films

Thin films are used in wide range of applications in industry, such as solar cells and LEDs. When thin films are deposited on substrates, various stresses are generated due to the mechanical difference between the film and substrate. These stresses can cause defects, such as cracking and buckling. Therefore, knowledge of the mechanical properties is important for improving their reliability and stability. In this study, the thermal expansion coefficient of FCC metallic thin films, such as Ag and Cu, which have different grain sizes and thicknesses, were calculated using the thermal cycling method. As a result, thermal expansion coefficient increased with increasing grain size. However, the film thickness had no remarkable effect.     

Mounted nanoporous anodic alumina thin films as planar optical waveguides

Solid-supported thin films of self-organized nanoporous anodic aluminum oxide (AAO) have been widely employed for the template preparation of nanostructured functional materials. Recently, the use of nanoporous AAO thin films in optical waveguide spectroscopy (OWS) has been explored for high sensitivity, in situ monitoring of processes occurring within these nanoporous templates. In this contribution, we demonstrate a strategy for mounting bulk anodized AAO thin films on heterogeneous solid-supports suitable for waveguide sensing experiments. Unlike conventional preparations of AAO thin films by anodization of vacuum- or electrochemically deposited Al thin films, the full range of techniques available to anodize bulk Al may potentially be applied with the present method. Moreover, we show that AAO thin films mounted on glass substrates can have superior waveguide coupling properties compared to conventionally prepared samples. The nanostructure of the AAO can be well characterized by an EMT-OWS analysis, demonstrated by comparing scanning electron microscopy images of the AAO and the pore dimensions calculated from an effective medium theory (EMT) analysis of the film refractive index measured by OWS. Finally, using a curved metallic substrate as an example, we show that our mounting technique can be used as a general strategy to functionalize objects with nanoporous AAO films.     

Ultrathin oxide films on metals: new physics and new chemistry?

Oxide thin films on metals are now currently used as model systems to study the surface properties of highly insulating oxides by means of electron spectroscopies. However, it has been recently proposed that ultrathin oxide films and oxide–metal interfaces may actually have unprecedented intrinsic chemical–physical properties, because of image potential screening of charge fluctuations and interfacial hybridizational effects. In fact, on-site Coulomb interactions and charge transfer energies in oxide thin films on metals are reduced by as much as a few eV as compared to the bulk values, thus suggesting a large reduction of the conductivity gap and a strong enhancement of the strength of various exchange and superexchange magnetic interactions in thin layers of strongly correlated oxides on metals. Moreover, interfacial oxygen states with strong metallic character have been observed and considered responsible for an unusually high and chemical selective reactivity of oxide–metal interfaces. Some basic ideas and results connected with these intriguing interfacial phenomena will be presented and discussed taking MgO thin films on Ag(100) as a model system.     

大块金属玻璃晶化过程的研究进展

大块金属玻璃具有许多独特的性能,有着广阔的应用前景.晶化过程对大块金属玻璃的应用有很大影响,是当前此领域研究的热点之一.介绍了大块金属玻璃在各种条件下晶化过程、影响因素等方面的研究进展.     

Changes of Structure and Bonding with Thickness in Chalcogenide Thin Films

Extreme miniaturization is known to be detrimental for certain properties, such as ferroelectricity in perovskite oxide films below a critical thickness. Remarkably, few-layer crystalline films of monochalcogenides display robust in-plane ferroelectricity with potential applications in nanoelectronics. These applications critically depend on the electronic properties and the nature of bonding in the 2D limit. A fundamental open question is thus to what extent bulk properties persist in thin films. Here, this question is addressed by a first-principles study of the structural, electronic, and ferroelectric properties of selected monochalcogenides (GeSe, GeTe, SnSe, and SnTe) as a function of film thickness up to 18 bilayers. While in selenides a few bilayers are sufficient to recover the bulk behavior, the Te-based compounds deviate strongly from the bulk, irrespective of the slab thickness. These results are explained in terms of depolarizing fields in Te-based slabs and the different nature of the chemical bond in selenides and tellurides. It is shown that GeTe and SnTe slabs inherit metavalent bonding of the bulk phase, despite structural and electronic properties being strongly modified in thin films. This understanding of the nature of bonding in few-layers structures offers a powerful tool to tune materials properties for applications in information technology.