The major challenge to overcome when processing metallic glasses (MGs) is to avoid crystallization. Therefore, time-temperature-transformation (TTT) diagrams are used, but they are often derived from ...experiments in which heating or cooling rates are limited and do not cover the full range of processing conditions, especially those encountered in additive manufacturing (AM) where the rates are very high. Here, an industrial-grade Zr-based MG (AMZ4) is investigated via fast differential scanning calorimetry (FDSC). The critical cooling and heating rates of AMZ4 are experimentally measured and TTT diagrams are determined upon heating and cooling. The critical heating rate of 45,000 K/s is 18 times the critical cooling rate, which indicates the presence of a self-doped glass (SDG) that includes quenched-in nuclei. The results illustrate that AMZ4 is very sensitive to crystallization, even in laser-based AM conditions, where heating and cooling steps need to be distinguished.
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Alloys of magnesium, zinc or iron that do not contain toxic elements are attractive as construction material for biodegradable implants, i.e., the type of implants that harmlessly dissolve away ...within the human body after they have completed their intended task. The synergistic influence of mechanical stress and corrosive human body fluid can cause sudden and catastrophic fracture of bioimplants due to phenomena such as stress corrosion cracking (SCC) and corrosion fatigue (CF). To date, SCC and CF of implants based on Zn have scarcely been investigated. This article is an overview of the challenges, research needs and way forward in understanding human body-fluid-assisted fractures (i.e., SCC and CF) of Zn alloys in human body fluid.
Micro- and nanoscale metallic glasses offer exciting opportunities for both fundamental research and applications in healthcare, micro-engineering, optics and electronics. The scientific and ...technological challenges associated with the fabrication and utilization of nanoscale metallic glasses, however, remain unresolved. Here, we present a simple and scalable approach for the fabrication of metallic glass fibres with nanoscale architectures based on their thermal co-drawing within a polymer matrix with matched rheological properties. Our method yields well-ordered and uniform metallic glasses with controllable feature sizes down to a few tens of nanometres, and aspect ratios greater than 10
. We combine fluid dynamics and advanced in situ transmission electron microscopy analysis to elucidate the interplay between fluid instability and crystallization kinetics that determines the achievable feature sizes. Our approach yields complex fibre architectures that, combined with other functional materials, enable new advanced all-in-fibre devices. We demonstrate in particular an implantable metallic glass-based fibre probe tested in vivo for a stable brain-machine interface that paves the way towards innovative high-performance and multifunctional neuro-probes.
Advancements in the design of mechanical blood circulatory devices have greatly improved patient survival rates, but currently employed metals still provoke a thrombosis response upon contact with ...blood, with potential life‐threatening consequences. While coating strategies have been developed to address this limitation, they possess inherent drawbacks such as susceptibility to crack formation and delamination. Herein, an amorphous metal based on palladium (Pd) is scrutinized and reveals substantial thrombogenic resistance compared to a state‐of‐the‐art titanium alloy. In vitro assessment with human whole blood shows that the Pd glass provokes reduced platelet activation (lower expression of CD62P, CD41/CD61) and greatly retarded fibrin formation, but pronounced platelet spreading therewith challenging the dogma that platelet spreading equals activation. Mechanistic analysis of the early biomaterial–blood interactions reveals that conformational changes of adhered fibrinogen, and modified αIIbβ3 integrin expression and distribution across adhered platelets, underlay the superior performance of Pd glass. The study is accompanied by structural and thermophysical bulk investigations and physicochemical surface characterization to link the materials properties with the observed blood response. The results reveal a remarkable potential of Pd‐based glass as direct blood‐contacting bulk material without the need for coating.
Metallic biomaterials are inevitable for the functioning of mechanical blood pumps but induce a thrombosis response upon contact with blood that can be life‐threatening. This work showcases an amorphous metal based on noble palladium that largely outperforms a state‐of‐the‐art titanium alloy. Through combination of material and biological investigations, this work unravels mechanistic insights underlying the low thrombogenicity of Pd‐based metallic glass.
Crystals do eventually melt if they are heated to their characteristic melting point. However, this is practically only the case for high‐temperature stable crystals, whereas low‐temperature ...metastable crystals generally transform, before melting, into a more stable solid during heating. Here, it is illustrated that low‐temperature crystals can, however, be melted via fast differential scanning calorimetry (FDSC), even in metallic systems where nucleation and growth kinetics are rapid. For a Au–Si eutectic alloy, various metastable and stable solid states, i.e., (Au–α), (Au–β), γ, and (Au–Si), which form under well‐controlled conditions and melt at high heating rates by preventing the metastable‐to‐stable solid phase transition, are isolated. It is demonstrated that Au81.4Si18.6 can fully melt at various temperatures, i.e., 294 °C, 312 °C, 352 °C, and 363 °C, with differing melting enthalpies ranging from 6.52 to 9.83 kJ mol−1. The melting and crystallization paths of the metastable solids are determined by constructing an energy−temperature diagram. This approach advances the general understanding of nucleation in metallic and other systems, and is expected to contribute to the detailed understanding of thermophysical phenomena that occur at spatially reduced dimensions and/or short time scales, for example in thin‐film deposition, nanomaterials production, or additive manufacturing.
Metastable solid states are isolated using novel experimental strategies via fast differential scanning calorimetry and melted at high heating rates by preventing the metastable‐to‐stable phase transition in a eutectic Au81.4Si18.6 alloy. An energy−temperature diagram is constructed from their distinct melting points and enthalpies to describe the alloy's multistep crystallization and melting pathways.
Titanium alloys are commonly used as biomaterials in musculoskeletal applications, but their long‐term efficacy can be limited by wear and corrosion, stress shielding, and bacterial colonization. As ...a promising alternative, bulk metallic glasses (BMGs) offer superior strength and corrosion resistance, but the influence of their chemical composition on their bioactivity remains largely unexplored. This study, therefore, aims to examine how the surface chemistry of palladium (Pd)‐, platinum (Pt)‐, and titanium (Ti)‐based BMGs can steer their response to biological systems. The chemical composition of BMGs governs their thermophysical and mechanical properties, with Pd‐based BMGs showing exceptional glass‐forming ability suitable for larger implants, and all BMGs exhibiting a significantly lower Young's modulus than Ti‐6Al‐4 V (Ti64), suggesting a potential to reduce stress shielding. Although BMGs feature copper depletion at the near surface, their surface chemistry remains more stable than that of Ti64 and supports blood biocompatibility. Fibrin network formation is heavily dependent on BMGs’ chemical composition and Ti‐based BMGs support thicker fibrin network formation than Ti64. Furthermore, BMGs outperform Ti64 in promoting mineralization of human bone progenitor cells and demonstrate antimicrobial properties against Staphylococcus aureus in a surface chemistry‐dependent manner, thereby indicating their great potential as biomaterials for musculoskeletal applications.
In musculoskeletal applications, palladium‐, platinum‐, and titanium‐based bulk metallic glasses (BMGs) offer the potential to reduce stress shielding in comparison to Ti‐6Al‐4 V. These BMGs exhibit superior biological responses, including blood biocompatibility, enhanced osteogenesis, and anti‐microbial activity, while the extent of these biological effects likely relies on their dynamics of chemical enrichment and depletion observed at the near surface.
This study demonstrates the metal-enhanced fluorescence of adenine using aluminum nanoparticle arrays in the deep UV range. It achieves the reproducible intensity enhancement of intrinsic ...fluorescence up to 80 on well-defined aluminum nanoparticle arrays at 257 nm excitation. In addition to a high signal enhancement, a strong modification of the fluorescence emission spectrum of adenine is observed. This study illustrates that the label-free detection of DNA bases and proteins that have low intrinsic fluorescence and absorption bands in the deep UV range can be facilitated using aluminum nanostructures.
Shear-Band Dynamics in Metallic Glasses Maas, Robert; Loffler, Jorg F
Advanced functional materials,
April 22, 2015, Letnik:
25, Številka:
16
Journal Article
Recenzirano
The future of metallic glasses as an advanced structural and functional material will to a great extent depend on the understanding and control of their mesoscopic flow defects called shear bands. ...These defects are sweet‐and‐sour; sweet because they mediate macroscopic plasticity at room temperature, and sour because they quickly promote failure. In the past decade, fundamental research generated great progress in characterizing the role that shear bands play during plastic deformation of disordered systems, including metallic glasses. Similar to those in many other materials, shear bands in metallic glasses are only active for a very short time, which directed research focus towards topological, structural, chemical, and thermal properties of formed, but inactive shear bands. In this paper, recent progress in directly characterizing the shear‐band dynamics in situ during straining experiments is presented. Various shear‐banding stages are outlined, including formation, propagation, and arrest, as well as shear‐band creep and aging. The results are discussed in a more general context of disordered materials, concluding with a summarizing overview of time‐scales involved in shear banding, and describing future research directions that may lead to controlled shear‐band plasticity in metallic glasses.
Dynamic properties of shear bands are a key element for the design of plastically stable bulk metallic glasses. In this Feature Article, recent progress on in situ characterization of shear‐band dynamics is summarized. The aim is to provide a comprehensive understanding of shear‐band initiation, propagation, arrest, creep, and aging, and how they determine the plastic flow behavior of bulk metallic glasses.
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