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This contribution shows an unusually high hydrogen storage of multilayer amorphous (A)-crystalline (C) Pd–Si based nanosheets when stacked in the right order. Samples with A/C/A/C/A stacking sequence exhibit 40 and 12 times larger hydrogen sorption than monolithic crystalline and amorphous samples, respectively. The maximum capacitance calculated from the fitting of electrochemical impedance measurements of the same sample is twice larger than that of the conventional polycrystalline Pd films of similar thickness. Five times higher diffusion coefficient calculated from modified Cottrell equation is obtained compared to specimens with C/A/C/A/C stacking. For the A/C/A/C/A multilayers, nanobubbles with diameters of 1–2 nm are homogeneously distributed at Si/SiO 2 interface, and PdH x crystal formation in these regions confirms hydrogen-metal interactions. Furthermore, corrosion-resistant amorphous top layer permits larger amounts of hydrogen ion transfer to inner layers. Thus, hydrogen storage and production can be enhanced by smart design of multilayers targeted for proton exchange membrane electrolysis or fuel cells. [Display omitted] • Ultra-high hydrogen storage in amorphous (A)-crystalline (C) Pd–Si based nanosheets. • Nanobubbles and PdH x crystal formation at metal-Si interface recorded by HR(S)TEM. • Corrosion-resistant amorphous top layer grants hydrogen ion transfer to inner layers. • Modified Cottrell equation yields five times higher diffusion in A/C/A/C/A stacking. • Maximum capacitance of A/C/A/C/A from ECM twice larger than crystal Pd thin film. [ABSTRACT FROM AUTHOR]

The formability difference between good and marginal glass-forming systems is investigated by micro-surface patterning of hierarchical features using thermoplastic net-shaping (TPN). For each alloy, a remarkable change in the flow behaviour is observed as the applied force along with the pressing time and temperature are optimized. The flow kinetics of glassy alloys with different glass-forming abilities is best described by the formability parameter S , which is defined by the ratio of the width of the supercooled to undercooled liquid region ( T l − T g )/( T x − T g ). Reproducible micro-engineered surfaces with high uniformity can be established by controlled TPN processing. [ABSTRACT FROM AUTHOR]

The development of bulk metallic glasses for biomedical applications has become the focus of intense research interest. In this work, we report on the unique thermoplastic behavior of two Ni-free Ti-based bulk metallic glasses by utilizing the dramatic softening of the amorphous structure in the super cooled liquid region. Ti 40 Zr 10 Cu 34 Pd 14 Ga 2 and Ti 40 Zr 10 Cu 34 Pd 14 Sn 2 bulk glassy alloys were produced by copper mold casting. Ga and Sn micro-alloying (2 at%) improve the glass-forming ability and mechanical properties of Ti 40 Zr 10 Cu 36 Pd 14 alloy effectively. The cast rods were thermo-mechanically characterized to determine the most suitable processing temperature and time, and the load that has to be applied for thermoplastic net-shaping of the BMGs into anisotropically etched cavities of silicon chips. Periodic features with high surface smoothness and uniform height (24 μm high circular bumps with sub-μm roughness) were created on the surface of the BMGs. The surface patterning with controllable roughness of Ti-based BMGs can be useful in biomedical studies by mediating material - cell interactions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Design of a new technique based on planar-flow melt-spinning for the fabrication of metallic glass microfibers. • The new technique is based on wetting and formation of thin film on rotating copper wheel followed by simultaneous rupture of the film into microfibers in the range of 1–20 µm. • The nature of the new technique makes it possible to fabricate fully amorphous structure from alloy compositions which are not designed for metallic glass formation. • We have shown and confirmed the formation of fully amorphous structure in µm-range, from Ti-stabilized 316 stainless steel. The amorphous structure is confirmed by XRD, DTA, TEM. • The hardness of the as-purchased stainless steel increased from ∼ 2.5 to ∼ 8.2 GPa after formation of the amorphous structure. • The subsequent stepwise heat-treatment on the amorphous stainless steel creates adjacent nanostructured and amorphous grains, observed by TEM. • The heat-treated stainless steel shows an even further increase in hardness to ∼ 14.2 Gpa. • We believe that both the confinement of dislocation movement in the nanocrystalline grains as well as the absence of dislocations in the amorphous grains contribute to this tremendous increase of hardness in heat-treated stainless steel. The high passivation capacity of austenitic stainless steel results in their excellent corrosion resistance. There are many ways to improve the hardness of austenitic stainless steel such as cold rolling or grain refinement. Herein, we explore the possibility of improving the hardness of AISI316-Ti stainless steel by generating an amorphous-nanocrystalline microstructure. First, we have utilized our modified melt-spinning technique to fabricate AISI316-Ti stainless steel microfibers with a fully amorphous structure. Formation of a fully amorphous structure was confirmed by using X-ray diffraction (XRD), differential thermal analysis (DTA), and transmission electron microscopy (TEM). Thermal analysis revealed a glass transition temperature of 437˚C followed by a crystallization peak of 573˚C. Nanoindentation analysis showed a fourfold increase of hardness from the initial value of ≈2.5 ± 0.1 GPa the starting AISI316-Ti stainless steel rod to the hardness of ≈8.2 ± 0.5 GPa for the amorphous AISI316-Ti structure. Further step-size heat treatment on melt-spun (amorphous) stainless steel microfibers generated a microstructure compromising adjacent nanocrystalline and amorphous grains as observed by TEM. Nanoindentation analysis of those fibers has shown an even greater increase in hardness, reaching an average value of ≈14.2 ± 1.0 GPa. We believe that both the confinement of dislocation movement in the nanocrystalline grains as well as the absence of dislocations in the amorphous grains contribute to this tremendous increase of hardness in stainless steel. [ABSTRACT FROM AUTHOR]

Owing to their extremely low shear viscosity and fragility, bulk metallic glasses (BMGs) are envisioned as new net-shaping material replacing conventionally used crystalline metals for various applications. The first part of this review describes the general technique and kinetics of thermoplastic forming. The second part elaborates on the thermal processing capability of metallic glasses from atomic- to meter-scale. The micro-/nano-structure obtained after various quenching rates followed by temperature, time and heating rate dependent thermoplastic forming is described in the third section. The deformation behavior and flow kinetics of BMGs in terms of composition, mold features, and applied conditions are elaborated in the fourth section. The variation of volume and enthalpy at the supercooled liquid region, strength retention of metallic glasses compared to other conventional metals and alloys, and kinetics of liquid fragility are given in the fifth section. Finite element modeling and molecular dynamics simulations of high-temperature deformation in BMGs are presented in the sixth part. Thermally-formed BMGs used for different applications, including energy, biomedical and micro-optics, are presented in the final part. Altogether, this review provides an overview of shaping capabilities and modifications in the macro-scale properties and short-to-medium range order of BMGs upon thermoplastic forming. [ABSTRACT FROM AUTHOR]

The correlation of a material's structure with its properties is one of the important unresolved issues in materials science research. This paper discusses a novel experimental and computational approach by which the influence of the pores on the mechanical properties of bulk metallic glasses (BMGs) can be systematically and quantitatively analyzed. The experimental stage involves the fabrication of a template whose pore configurations are pre-determined by computer-aided design tools, and replication of the designed patterns with BMGs. Quasi-static mechanical characterization of these complex microstructures is conducted under uniaxial tension and in-plane compression. For the numerical simulations, a non-local gradient-enhanced continuum mechanical model is established, using thermodynamic principles and periodic boundary conditions. The combination of the experimental and numerical results has identified the importance of the pore configuration, overall porosity and diameter to the spacing ratio of the pores to attain optimized material properties. [ABSTRACT FROM AUTHOR]

This contribution reveals ultra-high corrosion resistance of high entropy alloys (HEAs), i.e. Ti 20 Zr 20 Nb 15 V 15 Hf 15 Ta 15 of 1.85 µm yr–1 in alkaline environment, adverting their use for battery/fuel cell components. Formation of several nanometers passive oxide layer confirmed by scanning transmission electron microscopy accounts for corrosion resistance which increases with TiO x content. Cathodic Tafel slope of 67 mV dec–1 and large transfer coefficient of 0.82 obtained for Ti 20 Zr 20 Nb 20 V 20 Ta 20 suggest its use for hydrogen electrocatalysis. High amounts of hydrogen storage, 1.7 wt% in Ti 25 Zr 25 Nb 15 V 15 Ta 20 , were confirmed by gas-solid reactions. This HEA also has high corrosion resistance in acidic and saline environments ideal for coatings and surgical tools/implants. [Display omitted] • Ultra-high corrosion resistance down to 1.85 µm yr–1 of TiZrNbVTa(Hf) HEAs in 1 M KOH. • Formation of a few nanometers passive oxide layer accounts for corrosion stability. • High hydrogen activity due to low cathodic Tafel slope & large transfer coefficient. • Gas-solid reactions confirm high hydrogen storage of 1.7 wt%. • High corrosion stability in 0.5 M H 2 SO 4 (0.148 mm yr–1) & 0.9 wt% NaCl (0.081 mm yr–1). [ABSTRACT FROM AUTHOR]

The hydrogenation and oxide formation behavior of Fe–Ni-based metallic glasses (MGs), where measurements by the conventional gas-solid reaction method are difficult, is analyzed by a two-step approach: chronoamperometry followed by cyclic voltammetry (CA + CV). We introduce a concept of effective volume by measuring the thickness of the region where the hydrogen and hydroxyl ion interactions with Fe-based MG take place, which is characterized by high-angle annular dark-field scanning transmission electron microscopy. A very constant film thickness influenced by the OH− and H+ is confirmed by TEM, where the chemical homogeneity is maintained within this region. The weight percent of hydrogen and the corresponding hydrogen-to-metal ratio are determined as 1.16% and 0.56, respectively. When compared to previous studies conducted by the electrochemical-permeation method, the H/M ratio is found to be an order of magnitude larger. Electrochemical impedance spectroscopy (EIS) and subsequent equivalent circuit modeling (ECM) of the tested ribbons resolve the surface-diffusion processes for hydride formation and oxidation kinetics. This contribution provides a different perspective for the design and study of low-cost and high-performance amorphous nanofilms for hydrogen-energy applications, particularly when the common gas-adsorption methods are problematic. Image 1 • Electrochemical hydrogenation of FeNi-MGs is an alternative for gas-solid reactions. • Difference perspective for the study of low-cost and energy-efficient nanofilms. • Concept of effective volume from the region of hydrogen/hydroxyl ion interactions. • (H/M) max = 0.59, ~1500 times larger than that calculated from actual submerged volume. • Sorption capacity from frequency-dependent ECM becomes maximum at (H/M) max = 0.59 [ABSTRACT FROM AUTHOR]

Electrochemical hydrogen absorption in duplex steels is not fully understood. In this work, an in-situ synchrotron cross-sectional X-ray micro-diffraction analysis is performed on steel with comparable phase fractions of ferrite and austenite, coupled with electrolytic hydrogen charging. The results reveal that charging with a constant current density of 10 mA/cm² for 5 h leads to expanding the austenitic lattice to a depth of approximately 250 µm, up to ≥0.15 %. In contrast, the lattice parameter of the ferrite phase remains unchanged during this process. As the austenite expansion progresses, it generates different amounts of equivalent in-plane compressive stresses, which amount to approximately -150 and -450 MPa in the austenite and ferrite phases at the sample surface , respectively. Using a finite element model of grain interaction, this difference is qualitatively interpreted by mutual mechanical constraints between ferrite and austenite, as well as between the hydrogen-charged surface layer and the underlying material. [Display omitted] [ABSTRACT FROM AUTHOR]

The remarkable mechanical, chemical, and physical characteristics exhibited by metallic glasses (MGs), arising from their disordered atomic arrangement, present substantial application prospects in the aerospace industry, consumer electronics, biomedical implants and devices, sporting goods, etc. However, the brittleness introduced by highly localized shear bands poses a limitation to broader applications. A promising approach to overcome this limitation involves the development of metallic glass composites (MGCs) via introducing a second phase (or multiple phases) to impede shear band propagation, effectively enhancing MGs' plasticity. This review aims to provide a comprehensive overview of the advancements in methods and mechanisms for improving the plasticity of MGCs. It is divided into two main sections: one detailing the impact of in-situ second phases, such as glassy, quasi-crystal, and crystalline phases (nano- and micro-particles, dendrites, B2 phases, ceramic phases, etc.), on the plasticity of MGCs at different scales. The other section explores the influence of ex-situ second phases on the plasticity of MGCs, encompassing particles, fibers, interpenetrating phases, as well as laminated structures like nano-laminated architecture, coatings, and shrink-fit metal sleeves. Additionally, the review outlines challenges and future prospects in the quest for high plasticity MGCs at room temperature. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Thermoplastic net-shaping (TPN) of Ti 40 Zr 10 Cu 36 Pd 14 bulk metallic glass leads to > 100 K higher thermomechanical stability registered by dynamic mechanical analysis. • ∼100 nm surface layer comprised of titanium, copper and zirconium oxides form upon TPN identified by high-resolution transmission electron microscopy. • Compared to the as-cast state, TPNed glass shows lower corrosion and passivation current densities within 0.9 wt% NaCl. • Increase in surface hydrophobicity in TPNed glass is correlated with decrease in corrosion rates and increase in surface resistivity. • Formation of a nanoscale oxide layer on the TPNed samples leads to significantly higher cell attachments on the surface. The application of highly biocompatible advanced materials leads to fewer complications and more successful medical treatments. This study proposes Ti 40 Zr 10 Cu 36 Pd 14 bulk metallic glass (BMG) as an oral implant material and provides insights into its possible processing routes, where high-temperature compression molding via an optimized process is adopted to both evaluate the thermoplastic net-shaping kinetics and tune the specific properties of the alloy. We present processed BMGs and BMG composites of the same composition with improved thermomechanical stability, from which high strength retention at temperatures, compared to the cast glass, by above 100 K higher is registered via dynamic mechanical analysis. ∼100 nm thin surface layers comprised of Ti, Cu, and Zr oxides form at the surface of the alloys, as identified by high-resolution transmission microscopy. Also, ∼4 orders of magnitude lower passivation current density along with ∼2 orders of magnitude lower corrosion current density of the processed glass compared to the values of the as-cast state confirms an extremely high stability in a 0.9 wt% saline environment which can be linked to surface hydrophobicity. Cytocompatibility analysis conducted by seeding human gingival fibroblast cells directly onto the thermoplastically formed Ti 40 Zr 10 Cu 36 Pd 14 BMG reveals no adverse effect on cytocompatibility. On the other hand, the formation of a nanoscale oxide layer on the thermoplastically formed samples leads to significantly higher cell attachments on the surface. [ABSTRACT FROM AUTHOR]

Nanoindentation strain-rate jump testing was used to determine activation volumes and energies of various metallic glasses and composites. Three different single phase metallic glasses and three composites (two with amorphous/crystalline Cu and one with an amorphous/amorphous structure) were investigated. The state of the materials was additionally changed by varying the testing temperature between room temperature and 430 °C, by performing high pressure torsion and by thermal cycling. The results show that testing temperature is the main parameter controlling activation volume and energy, whereas material modifications by high pressure torsion and thermal cycling do not significantly affect them. [ABSTRACT FROM AUTHOR]

[Display omitted] • Five fully biocompatible Ti-based metallic glasses with different metalloid and soft metal content for a synergistic improvement in corrosion properties. • For Ti 40 Zr 40 bearing alloys the GFA drops due to the low negative enthalpy of mixing between Ti and Zr atoms. • With increasing Ti and decreasing Zr content, the maximum of the broad diffuse XRD peak shifts to higher 2-Theta angles. • Ti 60 Zr 20 Si 8 Ge 7 B 3 Sn 2 and Ti 50 Zr 30 Si 8 Ge 7 B 3 Sn 2 have a very high pitting potential and wider passivation region compared with other Ti-based MG alloys. We introduce five new biocompatible Ti-based metallic glass (MG) compositions with different metalloid and soft metal content for a synergistic improvement in corrosion properties. Without any potentially harmful elements such as Cu, Ni or Be, these novel alloys can eliminate the risk of inflammatory reaction when utilized for permanent medical implants. Excluding Cu, Ni or Be, which are essential for Ti-based bulk MG production, on the other hand, confines the glass-forming ability of novel alloys to a moderate level. In this study, toxic-element free MG alloys with significant metalloid (Si–Ge–B, 15–18 at.%) and minor soft element (Sn, 2–5 at.%) additions are produced in ribbon form using conventional single-roller melt spinning technique. Their glass-forming abilities and their structural and thermal properties are comparatively investigated using X-ray diffraction (XRD), synchrotron XRD and differential scanning calorimetry. Their corrosion resistance is ascertained in a biological solution to analyze their biocorrosion properties and compare them with other Ti-based bulk MGs along with energy dispersive X-ray. Ti 60 Zr 20 Si 8 Ge 7 B 3 Sn 2 and Ti 50 Zr 30 Si 8 Ge 7 B 3 Sn 2 MG ribbons present a higher pitting potential and passivation domain compared with other Ti-based MG alloys tested in similar conditions. Human mesenchymal stem cell metabolic activity and cytocompatibility tests confirm their outstanding cytocompatibility, outperforming Ti-Al6-V4. [ABSTRACT FROM AUTHOR]

The coarsening of primary silicon phases is one of the main challenges in the preparation and application of Al-high Si content alloys. In this work, AlSi40 alloys were manufactured by selective laser melting (SLM). The influence of ceramic nanoparticles on the morphology and size of primary Si phase(s) is investigated. With addition of ceramic nanoparticles, large snow-shaped primary Si changes towards a polygonal shape in coarse regions, while blocky primary Si in fine regions shows insignificant change. The size of primary Si in the modified alloy decreases by ~27.1% and ~25.2% in the respective coarse and fine regions compared to that of the unmodified alloy. Due to the refinement and smoothening of primary Si in the modified alloy, the microhardness distribution becomes homogeneous and an average value of ~233 HV 0.2 was obtained. The coefficient of friction (COF) value and the wear rate are ~0.44 and ~4.5 × 10−5 mm3N−1m−1, respectively. An ultimate compressive strength of ~0.76 GPa and a maximum compressive strain of ~7.99% are obtained, increasing by ~21.0% and ~18.0% compared to those of the unmodified alloy. The SLM-fabricated AlSi40 alloys upon heat treatment showed an improved plasticity and slightly decreased strength due to the coarsening of primary Si and grains, decreased solid solution of Si in the matrix as well as accommodation of residual stresses after heat treatment. • AlSi40 alloys modified with nanoparticles are processed by selective laser melting. • The effect of nanoparticles on the morphology and size of primary Si is studied. • The properties of AlSi40 alloys with and without nanoparticles are compared. • The underlying mechanism for improved properties of composites is revealed. [ABSTRACT FROM AUTHOR]