Cooperative Shear in Bulk Metallic Glass Composites Containing Metastable β-Ti Dendrites

We report a novel plastic deformation mechanism of bulk metallic glass composites (BMGCs) containing metastable β-Ti dendrites. Plastic deformation of the BMGCs beyond the ultimate tensile strength is mediated by cooperative shear events, which comprise a shear band in the glassy matrix and a continuous ω-Ti band with a thickness of ∼10  nm in the β-Ti dendrite. The cooperative shear leads to serrated shear avalanches. The formation of narrow ω-Ti bands is caused by high local strain rates during the cooperative shear. The cooperative shear mechanism enriches the deformation mechanisms of BMGCs and also deepens the understanding of ω-Ti formation.

High pressure torsion induced lowering of Young's modulus in high strength TNZT alloy for bio-implant applications

An exceptional combination of low Young's modulus (E ~68 GPa) and high flow strength (σ_f ~1 GPa) was achieved for a consolidated β-Ti-based metastable Ti-35Nb-7Zr-5Ta (TNZT) alloy subjected to room temperature high-pressure torsion (HPT). The mechanical properties of the alloy were studied by quasistatic nanoindentation tests at different strain rates, where a reduction in Young's modulus E ~73 GPa (N_HPT¹⁰) and E ~68 GPa (N_HPT⁴⁰) is observed together with an increase in plastic deformability (or HPT rotations). The microstructure evolution with increasing shear strain has been investigated. The stabilized bcc β-Ti phase with homogeneous nanostructure distribution was observed leading to a low Young's modulus. Severe straining causes a uniform hardness distribution without any noticeable change in the strength of the material. This study may be useful for developing excellent removable implant materials.

Ductile bulk metallic glass by controlling structural heterogeneities

A prerequisite to utilize the full potential of structural heterogeneities for improving the room-temperature plastic deformation of bulk metallic glasses (BMGs) is to understand their interaction with the mechanism of shear band formation and propagation. This task requires the ability to artificially create heterogeneous microstructures with controlled morphology and orientation. Here, we analyze the effect of the designed heterogeneities generated by imprinting on the tensile mechanical behavior of the Zr_52.5Ti₅Cu₁₈Ni_14.5Al₁₀ BMG by using experimental and computational methods. The imprinted material is elastically heterogeneous and displays anisotropic mechanical properties: strength and ductility increase with increasing the loading angle between imprints and tensile direction. This behavior occurs through shear band branching and their progressive rotation. Molecular dynamics and finite element simulations indicate that shear band branching and rotation originates at the interface between the heterogeneities, where the characteristic atomistic mechanism responsible for shear banding in a homogeneous glass is perturbed.

Elastostatic reversibility in thermally formed bulk metallic glasses: nanobeam diffraction fluctuation electron microscopy

The unparalleled shaping ability of bulk metallic glasses can revolutionize commercial products having multi-length scale features with a processing time of several minutes. Despite the widespread shaping ability of these polymer-like multicomponent alloys, thermoplastic forming (TPF) can severely degrade the intrinsic properties, particularly when complex stress states are activated. The present work emphasizes the importance of elastostatic loading (ESL) which not only fully reverses deteriorated room temperature plasticity originating under TPF or post-cryostatic conditions, but also activates a rejuvenation mechanism by rendering an extended resistance against strain softening. Furthermore, the reduction in the supercooled liquid region and crystallization enthalpy measured by differential scanning calorimetry are found to be temporary, and can be fully reversed to the initial condition. HRTEM imaging of the samples are performed with an imaging spherical aberration corrector. Individual nanobeam diffraction patterns obtained by the fluctuation electron microscopy (FEM) measurements are acquired using a scanning transmission electron microscope with a probe size of 1.2 nm from a 10 × 10 raster, yielding 100 diffraction patterns. The normalized variance of a series of nanodiffraction patterns of the post-elastostatically loaded sample reveals a height decrease in the first broad peak of normalized intensity variance V(k) suggesting modifications in the medium-range structural order which in turn dramatically restores the mechanical and thermal properties. Overall, the combination of TPF and post-ESL treatment in advanced glassy metals can open a new avenue for ultra-high mechanical and thermal performance micro- and nanomechanical devices for biosensors, MOSFETs and robotics.

Influence of the Ag concentration on the medium-range order in a CuZrAlAg bulk metallic glass

Fluctuation electron microscopy of bulk metallic glasses of CuZrAl(Ag) demonstrates that medium-range order is sensitive to minor compositional changes. By analyzing nanodiffraction patterns medium-range order is detected with crystal-like motifs based on the B2 CuZr structure and its distorted structures resembling the martensitic ones. This result demonstrates some structural homology between the metallic glass and its high temperature crystalline phase. The amount of medium-range order seems slightly affected with increasing Ag concentration (0, 2, 5 at.%) but the structural motifs of the medium-range ordered clusters become more diverse at the highest Ag concentration. The decrease of dominant clusters is consistent with the destabilization of the B2 structure measured by calorimetry and accounts for the increased glass-forming ability.

Deformation mechanisms to ameliorate the mechanical properties of novel TRIP/TWIP Co-Cr-Mo-(Cu) ultrafine eutectic alloys

In the present study, the microstructural evolution and the modulation of the mechanical properties have been investigated for a Co-Cr-Mo (CCM) ternary eutectic alloy by addition of a small amount of copper (0.5 and 1 at.%). The microstructural observations reveal a distinct dissimilarity in the eutectic structure such as a broken lamellar structure and a well-aligned lamellar structure and an increasing volume fraction of Co lamellae as increasing amount of copper addition. This microstructural evolution leads to improved plasticity from 1% to 10% without the typical tradeoff between the overall strength and compressive plasticity. Moreover, investigation of the fractured samples indicates that the CCMCu alloy exhibits higher plastic deformability and combinatorial mechanisms for improved plastic behavior. The improved plasticity of CCMCu alloys originates from several deformation mechanisms; i) slip, ii) deformation twinning, iii) strain-induced transformation and iv) shear banding. These results reveal that the mechanical properties of eutectic alloys in the Co-Cr-Mo system can be ameliorated by micro-alloying such as Cu addition.

[Imaging in structural heart disease : Impact on interventional therapy]

For the treatment of structural heart disease, current options in the catheterization laboratory include MitraClip® implantation for treating severe mitral regurgitation, transcatheter aortic valve implantation (TAVI), closure of a patent foramen ovale (PFO) and occlusion of the left atrial appendage (LAA). These treatment options are based on a precise diagnosis provided by modern cardiac imaging, which is indispensable for treatment recommendations. Its importance for supporting the invasive procedures in the catheterization laboratory is less well known. Due to enhanced soft tissue characterization, it complements fluoroscopy and invasive angiography and thus enormously improves the safety of the procedures. In addition, it allows individualized follow-up care. The current article gives an overview of the clinically most frequently used procedures.

Historical Aspects of Echinococcosis

Echinococcosis is a zoonosis whose history dates back to antiquity. This article provides an overview on the general history of echinococcosis, including the elucidation of Echinococcus life cycles and the long controversy on the aetiology of the cystic and alveolar forms of echinococcosis (CE and AE), lasting about 100years since the middle of the 19th century. Furthermore, selected historical aspects of some fields of echinococcosis research are discussed and compared with our current knowledge, such as geographic distribution and epidemiology of CE (Echinococcus granulosus) and AE (Echinococcus multilocularis), clinical aspects and pathology, diagnosis in humans and animals, treatment (with focus on chemotherapy), control and basic research. A short paragraph is devoted to the neotropical forms of echinococcosis, caused by Echinococcus vogeli and Echinococcus oligarthrus. In this context the achievements of some ancestral pioneers of echinococcosis research are particularly highlighted and appreciated. Finally, the role of associations, international organizations (World Health Organization and others) and international working groups in echinococcosis research and control is briefly outlined. The retrospective reveals both the admirable achievements of our ancestors and the scientific progress of more recent times. But, it also shows the gaps in our knowledge, skills and resources that we need to control or even eradicate echinococcosis.

Effect of thermomechanical processing on the mechanical biofunctionality of a low modulus Ti-40Nb alloy

Different hardening strategies were evaluated regarding their potential to improve the mechanical biofunctionality of the cast and solution-treated low modulus β-Ti alloy Ti 40Nb. The strategies are based on thermomechanical treatments comprised of different hot- and cold-rolling steps, as well as annealing treatments aiming at the successive exploitation of different hardening mechanisms (grain boundary hardening, work hardening and precipitation hardening). Quasi-static tensile testing revealed that grain refinement by one order of magnitude has only a small impact on improving the mechanical biofunctionality of Ti-40Nb. However, work hardening effectively improves the tensile strength by 30% to a value of 650MPa, while retaining Young׳s modulus at 60GPa. The α-phase precipitation hardening was verified to have an increasing effect on both, strength and Young׳s modulus. Thereby, the change of Young׳s modulus dominates the change of the strength, even at low α-phase fractions. The pseudo-elastic behavior of Ti 40Nb is discussed under consideration of the microstructural changes due to the thermomechanical treatment. The texture changes evolving upon cold-rolling markedly influence the recrystallization behavior. However, the present results do not show a significant effect of the texture on the mechanical properties of Ti-40Nb.

Brittle-to-Ductile Transition in Metallic Glass Nanowires

When reducing the size of metallic glass samples down to the nanoscale regime, experimental studies on the plasticity under uniaxial tension show a wide range of failure modes ranging from brittle to ductile ones. Simulations on the deformation behavior of nanoscaled metallic glasses report an unusual extended strain softening and are not able to reproduce the brittle-like fracture deformation as found in experiments. Using large-scale molecular dynamics simulations we provide an atomistic understanding of the deformation mechanisms of metallic glass nanowires and differentiate the extrinsic size effects and aspect ratio contribution to plasticity. A model for predicting the critical nanowire aspect ratio for the ductile-to-brittle transition is developed. Furthermore, the structure of brittle nanowires can be tuned to a softer phase characterized by a defective short-range order and an excess free volume upon systematic structural rejuvenation, leading to enhanced tensile ductility. The presented results shed light on the fundamental deformation mechanisms of nanoscaled metallic glasses and demarcate ductile and catastrophic failure.

Low Young's modulus Ti-based porous bulk glassy alloy without cytotoxic elements

A new a biocompatible Ti42Zr40Ta3Si15 (atomic %) porous bulk glassy alloy was produced by combination of rapid solidification and powder metallurgy techniques. Amorphous alloy ribbons were fabricated by melt spinning, i.e. extremely fast quenching the molten alloy with 10(6)K/s from T=1973K down to room temperature. The ribbons were then cryo-milled at liquid nitrogen temperature in order to produce powder, which was subsequently hot pressed. The resulting thick pellets have a porosity of about 14vol%, a high compression strength of 337MPa and a Young's modulus of about E=52GPa, values very close to those characteristic of cortical bone. Moreover, the morphology of the samples is very similar to that of cortical bone. The biocompatibility, which is due to the absence of any toxic element in the chemical composition, together with the suitable mechanical behavior, make these samples promising for orthopedic and dentistry applications.

STATEMENT OF SIGNIFICANCE

Ti-based alloys are nowadays the standard solution for biomedical implants. However, both the conventional crystalline and amorphous alloys have higher rigidity as the human bone, leading to the damage of the bone at the interface, and contains harmful elements like vanadium, aluminum, nickel or beryllium. The hierarchical porous structures based on glassy alloys with biocompatible elements is a much better alternative. This work presents for the first time the manufacturing of such porous bodies starting from Ti-based amorphous alloy ribbons, which contains only non-harmful elements. The morphology and the compressive mechanical properties of these new products are analyzed in regard with those characteristic to the cortical bone.

Two-phase quasi-equilibrium in β-type Ti-based bulk metallic glass composites

The microstructural evolution of cast Ti/Zr-based bulk metallic glass composites (BMGCs) containing β-Ti still remains ambiguous. This is why to date the strategies and alloys suitable for producing such BMGCs with precisely controllable volume fractions and crystallite sizes are still rather limited. In this work, a Ti-based BMGC containing β-Ti was developed in the Ti-Zr-Cu-Co-Be system. The glassy matrix of this BMGC possesses an exceptional glass-forming ability and as a consequence, the volume fractions as well as the composition of the β-Ti dendrites remain constant over a wide range of cooling rates. This finding can be explained in terms of a two-phase quasi-equilibrium between the supercooled liquid and β-Ti, which the system attains on cooling. The two-phase quasi-equilibrium allows predicting the crystalline and glassy volume fractions by means of the lever rule and we succeeded in reproducing these values by slight variations in the alloy composition at a fixed cooling rate. The two-phase quasi-equilibrium could be of critical importance for understanding and designing the microstructures of BMGCs containing the β-phase. Its implications on the nucleation and growth of the crystalline phase are elaborated.

Enhanced polysulphide redox reaction using a RuO2 nanoparticle-decorated mesoporous carbon as functional separator coating for advanced lithium–sulphur batteries

A multi-functional RuO₂ nanoparticle-embedded mesoporous carbon-coated separator is used as an electrocatalytic and adsorbing polysulphide-net to enhance the redox reaction of migrating polysulphides.

Nanostructured Ti-Zr-Pd-Si-(Nb) bulk metallic composites: Novel biocompatible materials with superior mechanical strength and elastic recovery

The microstructure, mechanical behaviour, and biocompatibility (cell culture, morphology, and cell adhesion) of nanostructured Ti45 Zr15 Pd35- x Si5 Nbx with x = 0, 5 (at. %) alloys, synthesized by arc melting and subsequent Cu mould suction casting, in the form of rods with 3 mm in diameter, are investigated. Both Ti-Zr-Pd-Si-(Nb) materials show a multi-phase (composite-like) microstructure. The main phase is cubic β-Ti phase (Im3m) but hexagonal α-Ti (P63/mmc), cubic TiPd (Pm3m), cubic PdZr (Fm3m), and hexagonal (Ti, Zr)5 Si3 (P63/mmc) phases are also present. Nanoindentation experiments show that the Ti45 Zr15 Pd30 Si5 Nb5 sample exhibits lower Young's modulus than Ti45 Zr15 Pd35 Si5 . Conversely, Ti45 Zr15 Pd35 Si5 is mechanically harder. Actually, both alloys exhibit larger values of hardness when compared with commercial Ti-40Nb, (HTi-Zr-Pd-Si ≈ 14 GPa, HTi-Zr-Pd-Si-Nb ≈ 10 GPa and HTi-40Nb ≈ 2.7 GPa). Concerning the biological behaviour, preliminary results of cell viability performed on several Ti-Zr-Pd-Si-(Nb) discs indicate that the number of live cells is superior to 94% in both cases. The studied Ti-Zr-Pd-Si-(Nb) bulk metallic system is thus interesting for biomedical applications because of the outstanding mechanical properties (relatively low Young's modulus combined with large hardness), together with the excellent biocompatibility.

Chemical vapor deposition of twisted bilayer and few-layer MoSe₂ over SiO(x) substrates

The chemical vapor deposition of monolayer and few-layer transition metal dichalcogenides is a rapidly developing area of materials science due to the exciting electrical, optical, thermal and mechanical properties of transition metal dichalcogenides in their layered form. These properties make these innovative materials potentially relevant to wide-ranging commercial applications. One of these promising materials is MoSe₂; however, just recently, a few research groups have been able to demonstrate its synthesis via chemical vapor deposition. Moreover, only oriented few-layer MoSe₂ has been exhibited by synthetically formed material using chemical vapor deposition thus far. Here, we confirm twisted-layer MoSe₂ can also form during chemical vapor deposition. Twisted-layer transition metal dichalcogenides alter their properties as compared to their oriented counterparts. Therefore, twisted-layer structures are of interest because they can tune their properties.

Correlation between atomic structure evolution and strength in a bulk metallic glass at cryogenic temperature

A model Zr_41.25Ti_13.75Ni₁₀Cu_12.5Be_22.5 (at.%) bulk metallic glass (BMG) is selected to explore the structural evolution on the atomic scale with decreasing temperature down to cryogenic level using high energy X-ray synchrotron radiation. We discover a close correlation between the atomic structure evolution and the strength of the BMG and find out that the activation energy increment of the concordantly atomic shifting at lower temperature is the main factor influencing the strength. Our results might provide a fundamental understanding of the atomic-scale structure evolution and may bridge the gap between the atomic-scale physics and the macro-scale fracture strength for BMGs.

WITHDRAWN: Corrigendum to "World Association for the Advancement of Veterinary Parasitology (WAAVP): The 50th anniversary in 2013-History, achievements, and future perspectives" [Vet. Parasitol. 195 (2013) 206-217]

The Publisher regrets that this article is an accidental duplication of an article that has already been published, http://dx.doi.org/10.1016/j.vetpar.2013.12.026. The duplicate article has therefore been withdrawn.

Metallographic Preparation of Aluminium-Titanium Composites

There is no method that allows the simultaneous preparation of titanium and aluminum, so that both phases can be investigated by means of scanning electron microscopy (SEM) at the same time. Especially local orientation measurements by electron back scatter diffraction (EBSD) are challenging as they require a very good surface quality. This study deals with the preparation of aluminum/titanium composites, produced by Accumulative Roll Bonding (ARB) as well as with their microstructural analysis emphasing on the metallographic sample preparation. Well established routes of metallographic preparation for aluminum and titanium are facing serious problems such as rounding of edges, arising of deformation layers, blurred layers and oxide layers. This is of particular concern when these routes are applied to Al/Ti multilayered samples without adaption. This study reveals a route for metallographic sample preparation that enables SEM including EBSD analyses of Al/Ti composites for both phases simultaneously.

Chemical nanoroughening of Ti40Nb surfaces and its effect on human mesenchymal stromal cell response

Samples of low modulus beta-type Ti40Nb and cp2-Ti were chemically treated with 98% H2 SO4 + 30% H2 O2 (vol. ratio 1:1) solution. Surface analytical studies conducted with HR-SEM, AFM, and XPS identified a characteristic nanoroughness of the alloy surface related with a network of nanopits of ∼25 nm diameter. This is very similar to that obtained for cp2-Ti. The treatment enhances the oxide layer growth compared to mechanically ground states and causes a strong enrichment of Nb2 O5 relative to TiO2 on the alloy surface. The in vitro analyses clearly indicated that the chemical treatment accelerates the adhesion and spreading of human mesenchymal stromal cells (hMSC), increases the metabolic activity, and the enzyme activity of tissue non-specific alkaline phosphatase (TNAP). Surface structures which were generated mimic the cytoplasmic projections of the cells on the nanoscale. Those effects are more pronounced for the Ti40Nb alloy than for cp2-Ti. The relation between alloy surface topography and chemistry and cell functions is discussed.

Phase separation in ternary Co-Gd-Ti liquids

The phase equilibria and the solidification behavior of ternary Co-Gd-Ti (Co ≤35 at.%) alloys have been investigated. The phase transformation and equilibria in the liquid phase were studied in situ for two alloys, Co30Gd35Ti35 and Co30Gd50Ti20, by combining electrostatic levitation of the samples with high-energy synchrotron x-ray diffraction (XRD) at elevated temperature. The XRD patterns with two diffuse maxima for molten Co30Gd35Ti35 give direct evidence for liquid-liquid phase separation in this composition. In contrast, no indication for phase separation in the Co30Gd50Ti20 alloy is detected. Coarsened microstructures, typical for the phase-separating systems, are observed for the Co30Gd35Ti35, Co25Gd37.5Ti37.5, Co10Gd45Ti45 and Co30Gd20Ti50 cast alloys. Our findings suggest that the stable miscibility gap of binary Gd-Ti extends into the ternary Co-Gd-Ti system (up to about 30 at.% Co). Thermodynamic calculations of the ternary Co-Gd-Ti system by the CALPHAD method are in good agreement with the experimental results.

Origin of intermittent plastic flow and instability of shear band sliding in bulk metallic glasses

Intermittent or serrated plastic flow is widely observed in the deformation of bulk metallic glasses (BMGs) or other disordered solids at low temperatures. However, the underlying physical process responsible for the phenomena is still poorly understood. Here, we give an interpretation of the serrated flow behavior in BMGs by relating the atomic-scale deformation with the macroscopic shear band behavior. Our theoretical analysis shows that serrated flow in fact arises from an intrinsic dynamic instability of the shear band sliding, which is determined by a critical stiffness parameter in stick-slip dynamics. Based on this, the transition from serrated to nonserrated flow with the strain rate or the temperature is well predicted and the effects of various extrinsic and intrinsic factors on shear band stability can be quantitatively analyzed in BMGs. Our results, which are verified by a series of compression tests on various BMGs, provide key ingredients to fundamentally understand serrated flow and may bridge the gap between the atomic-scale physics and the larger-scale shear band dynamics governing the deformation of BMGs.

Porous low modulus Ti40Nb compacts with electrodeposited hydroxyapatite coating for biomedical applications

Porous ß-type non-toxic Ti40Nb alloy was prepared by compaction of mechanically alloyed powder mixed with NaCl or Mg particles as space-holder material. The compacts with porosity of 36-80% demonstrated a very low Young's modulus of ~1.5-3 GPa and compression strength of ~10-35 MPa, which is suitable for potential implant material application. Porous samples were electrochemically covered with hydroxyapatite. The influence of the deposition time and of the electrolyte concentrations on the morphology of the hydroxyapatite coating was studied. It is demonstrated that a homogenous coating of hydroxyapatite crystals with different shape and size can be obtained on the surface of the porous samples.

Structural investigations of Ge5As(x)Se(95-x) and Ge15As(x)Se(85-x) glasses using x-ray diffraction and extended x-ray fine structure spectroscopy

The structure of Ge(5)As(x)Se(95-x) (x = 10, 20, 30, 38 at.%) and Ge(15)As(x)Se(85-x) (x = 10, 25, 34 at.%) glasses has been investigated by high-energy x-ray diffraction and extended x-ray absorption fine structure measurements. The experimental datasets have been modelled using the reverse Monte Carlo simulation technique. The model atomic configurations have been analysed in detail. It has been found that the homonuclear Ge-Ge, As-As, Se-Se and heteronuclear Ge-As bonds play an important role in the structure formation of the Ge-As-Se glasses. The total number of these bonds decreases quite slowly with the mean coordination number similarly to the nonlinear refractive index.